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| − | <p>A <strong>gene</strong> is a locatable region of genomic sequence, corresponding to a unit of inheritance, which is associated with regulatory regions, transcribed regions and/or other functional sequence regions.<sup class="reference" id="_ref-Pearson_2006_0">[1]</sup><sup class="reference" id="_ref-Rethink_0">[2]</sup> The physical development and phenotype of organisms can be thought of as a product of genes interacting with each other and with the environment<sup class="reference" id="_ref-0">[3]</sup> A concise definition of gene taking into account complex patterns of regulation and transcription, genic conservation and non-coding RNA genes, has been proposed by Gerstein et al.<sup class="reference" id="_ref-Gerstein_2007_0">[4]</sup> "A gene is a union of genomic sequences encoding a coherent set of potentially overlapping functional products".</p> | + | 정의<br />-[[유전자]]<br /><br /> |
| − | <p>Colloquially, the term <strong>gene</strong> is often used to refer to an inheritable trait which is usually accompanied by a phenotype as in ("tall genes" or "bad genes") -- the proper scientific term for this is allele.</p>
| + | <p style=" LINE- HEIGHT: 20px" align=" left"><a name=" NDTITLE">< font size="2"> 염색체상에서 일정한 위치를 차지하고 있는 유전정보의 단위.</font></a></p> |
| − | <p>In cells, genes consist of a long strand of DNA that contains a promoter, which controls the activity of a gene, and coding and non-coding sequence. Coding sequence determines what the gene produces, while non-coding sequence can regulate the conditions of gene expression. When a gene is active, the coding and non-coding sequence is copied in a process called transcription, producing an RNA copy of the gene's information. This RNA can then direct the synthesis of proteins via the genetic code. However, RNAs can also be used directly, for example as part of the ribosome. These molecules resulting from gene expression, whether RNA or protein, are known as gene products.</p>
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| − | <p>Genes often contain regions that do not encode products, but regulate gene expression. The genes of eukaryotic organisms can contain regions called introns that are removed from the messenger RNA in a process called splicing. The regions encoding gene products are called exons. In eukaryotes, a single gene can encode multiple proteins, which are produced through the creation of different arrangements of exons through <em>alternative splicing</em>. In prokaryotes (bacteria and archaea), introns are less common and genes often contain a single uninterrupted stretch of DNA, called a <em>cistron</em>, that codes for a product. Prokaryotic genes are often arranged in groups called operons with promoter and operator sequences that regulate transcription of a single long RNA. This RNA contains multiple coding sequences. Each coding sequence is preceded by a Shine-Dalgarno sequence that ribosomes recognize.</p>
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| − | <p>The total set of genes in an organism is known as its genome. An organism's genome size is generally lower in prokaryotes, both in number of base pairs and number of genes, than even single-celled eukaryotes. However, there is no clear relationship between genome sizes and complexity in eukaryotic organisms. One of the largest known genomes belongs to the single-celled amoeba <em>Amoeba dubia</em>, with over 670 billion base pairs, some 200 times larger than the human genome.<sup class="reference" id="_ref-Cavalier-Smith_0">[5]</sup> The estimated number of genes in the human genome has been repeatedly revised downward since the completion of the Human Genome Project; current estimates place the human genome at just under 3 billion base pairs and about 20,000–25,000 genes.<sup class="reference" id="_ref-IHSGC2004_0"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-IHSGC2004">[6]</a></sup> A recent <em><a title="Science (journal)" href="http://en.wikipedia.org/wiki/Science_%28journal%29">Science</a></em> article gives a final number of 20,488, with perhaps 100 more yet to be discovered .<sup class="reference" id="_ref-gene_count2007_0"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-gene_count2007">[7]</a></sup> The gene density of a genome is a measure of the number of genes per million base pairs (called a megabase, Mb); prokaryotic genomes have much higher gene densities than eukaryotes. The gene density of the human genome is roughly 12–15 genes/Mb.<sup class="reference" id="_ref-Watson_2004_0"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-Watson_2004">[8]</a></sup></p>
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| − | <p><span class="mw-headline"><font size="5"><br />
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| − | History</font></span></p>
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| − | <p>The existence of genes was first suggested by <a title="Gregor Mendel" href="http://en.wikipedia.org/wiki/Gregor_Mendel">Gregor Mendel</a> (1822-1884), who, in the <a title="1860s" href="http://en.wikipedia.org/wiki/1860s">1860s</a>, studied inheritance in <a title="Pea" href="http://en.wikipedia.org/wiki/Pea">pea</a> plants and <a title="Hypothesis" href="http://en.wikipedia.org/wiki/Hypothesis">hypothesized</a> a factor that conveys traits from parent to offspring. He spent over 10 years of his life on one experiment. Although he did not use the term <em>gene</em>, he explained his results in terms of inherited characteristics. Mendel was also the first to hypothesize <a class="mw-redirect" title="Independent assortment" href="http://en.wikipedia.org/wiki/Independent_assortment">independent assortment</a>, the distinction between <a class="mw-redirect" title="Dominant gene" href="http://en.wikipedia.org/wiki/Dominant_gene">dominant</a> and <a class="mw-redirect" title="Recessive" href="http://en.wikipedia.org/wiki/Recessive">recessive</a> traits, the distinction between a <a class="mw-redirect" title="Heterozygote" href="http://en.wikipedia.org/wiki/Heterozygote">heterozygote</a> and <a class="mw-redirect" title="Homozygote" href="http://en.wikipedia.org/wiki/Homozygote">homozygote</a>, and the difference between what would later be described as <a title="Genotype" href="http://en.wikipedia.org/wiki/Genotype">genotype</a> and <a title="Phenotype" href="http://en.wikipedia.org/wiki/Phenotype">phenotype</a>. Mendel's concept was given a name by <a title="Hugo de Vries" href="http://en.wikipedia.org/wiki/Hugo_de_Vries">Hugo de Vries</a> in 1889, who, at that time probably unaware of Mendel's work, in his book <em>Intracellular Pangenesis</em> coined the term "pangen" for "the smallest particle [representing] one hereditary characteristic"<sup class="reference" id="_ref-pangen_0"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-pangen">[9]</a></sup>. <a title="Wilhelm Johannsen" href="http://en.wikipedia.org/wiki/Wilhelm_Johannsen">Wilhelm Johannsen</a> abbreviated this term to "gene" ("gen" in Danish and German) two decades later.</p>
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| − | <p>In the early 1900s, Mendel's work received renewed attention from scientists. In 1910, <a title="Thomas Hunt Morgan" href="http://en.wikipedia.org/wiki/Thomas_Hunt_Morgan">Thomas Hunt Morgan</a> showed that genes reside on specific <a title="Chromosome" href="http://en.wikipedia.org/wiki/Chromosome">chromosomes</a>. He later showed that genes occupy specific locations on the chromosome. With this knowledge, Morgan and his students began the first chromosomal map of the fruit fly <em><a title="Drosophila melanogaster" href="http://en.wikipedia.org/wiki/Drosophila_melanogaster">Drosophila</a></em>. In 1928, <a title="Frederick Griffith" href="http://en.wikipedia.org/wiki/Frederick_Griffith">Frederick Griffith</a> showed that genes could be transferred. In what is now known as <a title="Griffith's experiment" href="http://en.wikipedia.org/wiki/Griffith%27s_experiment">Griffith's experiment</a>, injections into a mouse of a deadly strain of <a title="Bacteria" href="http://en.wikipedia.org/wiki/Bacteria">bacteria</a> that had been heat-killed transferred genetic information to a safe strain of the same bacteria, killing the mouse.</p>
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| − | <p>In 1941, <a title="George Wells Beadle" href="http://en.wikipedia.org/wiki/George_Wells_Beadle">George Wells Beadle</a> and <a title="Edward Lawrie Tatum" href="http://en.wikipedia.org/wiki/Edward_Lawrie_Tatum">Edward Lawrie Tatum</a> showed that mutations in genes caused errors in certain steps in <a title="Metabolic pathway" href="http://en.wikipedia.org/wiki/Metabolic_pathway">metabolic pathways</a>. This showed that specific genes code for specific proteins, leading to the "one gene, one enzyme" hypothesis.<sup class="reference" id="_ref-Gerstein_0"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-Gerstein">[10]</a></sup> <a title="Oswald Avery" href="http://en.wikipedia.org/wiki/Oswald_Avery">Oswald Avery</a>, <a class="mw-redirect" title="Collin Macleod" href="http://en.wikipedia.org/wiki/Collin_Macleod">Collin Macleod</a>, and <a title="Maclyn McCarty" href="http://en.wikipedia.org/wiki/Maclyn_McCarty">Maclyn McCarty</a> showed in 1944 that DNA holds the gene's information. In 1953, <a title="James D. Watson" href="http://en.wikipedia.org/wiki/James_D._Watson">James D. Watson</a> and <a title="Francis Crick" href="http://en.wikipedia.org/wiki/Francis_Crick">Francis Crick</a> demonstrated the molecular structure of <a title="DNA" href="http://en.wikipedia.org/wiki/DNA">DNA</a>. Together, these discoveries established the <a title="Central dogma of molecular biology" href="http://en.wikipedia.org/wiki/Central_dogma_of_molecular_biology">central dogma of molecular biology</a>, which states that proteins are translated from <a title="RNA" href="http://en.wikipedia.org/wiki/RNA">RNA</a> which is transcribed from DNA. This dogma has since been shown to have exceptions, such as <a title="Reverse transcription" href="http://en.wikipedia.org/wiki/Reverse_transcription">reverse transcription</a> in <a title="Retrovirus" href="http://en.wikipedia.org/wiki/Retrovirus">retroviruses</a>.</p>
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| − | <p>In <a title="1972" href="http://en.wikipedia.org/wiki/1972">1972</a>, <a title="Walter Fiers" href="http://en.wikipedia.org/wiki/Walter_Fiers">Walter Fiers</a> and his team at the Laboratory of Molecular Biology of the <a class="mw-redirect" title="University of Ghent" href="http://en.wikipedia.org/wiki/University_of_Ghent">University of Ghent</a> (<a title="Ghent" href="http://en.wikipedia.org/wiki/Ghent">Ghent</a>, <a title="Belgium" href="http://en.wikipedia.org/wiki/Belgium">Belgium</a>) were the first to determine the sequence of a gene: the gene for <a title="Bacteriophage MS2" href="http://en.wikipedia.org/wiki/Bacteriophage_MS2">Bacteriophage MS2</a> coat protein.<sup class="reference" id="_ref-Min_1972_0"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-Min_1972">[11]</a></sup> <a title="Richard J. Roberts" href="http://en.wikipedia.org/wiki/Richard_J._Roberts">Richard J. Roberts</a> and <a class="mw-redirect" title="Phillip Sharp" href="http://en.wikipedia.org/wiki/Phillip_Sharp">Phillip Sharp</a> discovered in 1977 that genes can be split into segments. This leads to the idea that one gene can make several proteins. Recently (as of <a title="2003" href="http://en.wikipedia.org/wiki/2003">2003</a>-<a title="2006" href="http://en.wikipedia.org/wiki/2006">2006</a>), <a title="Biology" href="http://en.wikipedia.org/wiki/Biology">biological</a> results let the notion of gene appear more slippery. In particular, genes do not seem to sit side by side on <a title="DNA" href="http://en.wikipedia.org/wiki/DNA">DNA</a> like discrete beads. Instead, <a title="Region" href="http://en.wikipedia.org/wiki/Region">regions</a> of the DNA producing distinct proteins may overlap, so that the idea emerges that "genes are one long <a title="Continuum (theory)" href="http://en.wikipedia.org/wiki/Continuum_%28theory%29">continuum</a>".<sup class="reference" id="_ref-Pearson_2006_1"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-Pearson_2006">[1]</a></sup></p>
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| − | <p><a id="Mendelian_inheritance_and_classical_genetics" name="Mendelian_inheritance_and_classical_genetics"></a></p>
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| − | <h2><span class="editsection">[<a title="Edit section: Mendelian inheritance and classical genetics" href="http://en.wikipedia.org/w/index.php?title=Gene&action=edit&section=2">edit</a>]</span> <span class="mw-headline">Mendelian inheritance and classical genetics</span></h2>
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| − | <dl><dd>
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| − | <div class="noprint relarticle mainarticle"><em>Main articles: <a title="Mendelian inheritance" href="http://en.wikipedia.org/wiki/Mendelian_inheritance">Mendelian inheritance</a> and <a title="Classical genetics" href="http://en.wikipedia.org/wiki/Classical_genetics">Classical genetics</a></em></div>
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| − | </dd></dl>
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| − | <p>Darwin used the term <a title="Gemmule" href="http://en.wikipedia.org/wiki/Gemmule">Gemmule</a> to describe a microscopic unit of inheritance, and what would later become known as <a title="Chromosome" href="http://en.wikipedia.org/wiki/Chromosome">Chromosomes</a> had been observed separating out during cell division by <a title="Wilhelm Hofmeister" href="http://en.wikipedia.org/wiki/Wilhelm_Hofmeister">Wilhelm Hofmeister</a> as early as 1848. The idea that chromosomes were the carriers of inheritance was expressed in 1883 by <a title="Wilhelm Roux" href="http://en.wikipedia.org/wiki/Wilhelm_Roux">Wilhelm Roux</a>. The modern conception of the gene originated with work by <a title="Gregor Mendel" href="http://en.wikipedia.org/wiki/Gregor_Mendel">Gregor Mendel</a>, a <a title="19th century" href="http://en.wikipedia.org/wiki/19th_century">19th century</a> <a class="mw-redirect" title="Augustinian" href="http://en.wikipedia.org/wiki/Augustinian">Augustinian</a> monk who systematically studied heredity in pea plants. Mendel's work was the first to illustrate <a class="mw-redirect" title="Particulate inheritance" href="http://en.wikipedia.org/wiki/Particulate_inheritance">particulate inheritance</a>, or the theory that inherited traits are passed from one generation to the next in discrete units that interact in well-defined ways. <a title="Denmark" href="http://en.wikipedia.org/wiki/Denmark">Danish</a> <a class="mw-redirect" title="Botanist" href="http://en.wikipedia.org/wiki/Botanist">botanist</a> <a title="Wilhelm Johannsen" href="http://en.wikipedia.org/wiki/Wilhelm_Johannsen">Wilhelm Johannsen</a> coined the word "gene" in 1909 to describe these fundamental physical and functional units of heredity,<sup class="reference" id="_ref-genome_0"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-genome">[12]</a></sup> while the related word <a title="Genetics" href="http://en.wikipedia.org/wiki/Genetics">genetics</a> was first used by <a title="William Bateson" href="http://en.wikipedia.org/wiki/William_Bateson">William Bateson</a> in <a title="1905" href="http://en.wikipedia.org/wiki/1905">1905</a>.<sup class="reference" id="_ref-Gerstein_1"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-Gerstein">[10]</a></sup> The word was derived from <a class="mw-redirect" title="Hugo De Vries" href="http://en.wikipedia.org/wiki/Hugo_De_Vries">Hugo De Vries</a>' 1889 term <em>pangen</em> for the same concept,<sup class="reference" id="_ref-pangen_1"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-pangen">[9]</a></sup> itself a derivative of the word <em><a title="Pangenesis" href="http://en.wikipedia.org/wiki/Pangenesis">pangenesis</a></em> coined by <a title="Charles Darwin" href="http://en.wikipedia.org/wiki/Charles_Darwin">Darwin</a> (1868).<sup class="reference" id="_ref-Darwin_0"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-Darwin">[13]</a></sup> The word pangenesis is made from the <a title="Greek language" href="http://en.wikipedia.org/wiki/Greek_language">Greek</a> words <em>pan</em> (a prefix meaning "whole", "encompassing") and <em>genesis</em> ("birth") or <em>genos</em> ("origin").</p>
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| − | <p>According to the theory of Mendelian inheritance, variations in <a title="Phenotype" href="http://en.wikipedia.org/wiki/Phenotype">phenotype</a> - the observable physical and behavioral characteristics of an organism - are due to variations in <a title="Genotype" href="http://en.wikipedia.org/wiki/Genotype">genotype</a>, or the organism's particular set of genes, each of which specifies a particular trait. Different genes for the same trait, which give rise to different phenotypes, are known as <a title="Allele" href="http://en.wikipedia.org/wiki/Allele">alleles</a>. Organisms such as the pea plants Mendel worked on, along with many plants and animals, have two alleles for each trait, one inherited from each parent. Alleles may be <a class="mw-redirect" title="Dominant gene" href="http://en.wikipedia.org/wiki/Dominant_gene">dominant</a> or <a class="mw-redirect" title="Recessive gene" href="http://en.wikipedia.org/wiki/Recessive_gene">recessive</a>; dominant alleles give rise to their corresponding phenotypes when paired with any other allele for the same trait, while recessive alleles give rise to their corresponding phenotype only when paired with another copy of the same allele. For example, if the allele specifying tall stems in pea plants is dominant over the allele specifying short stems, then pea plants that inherit one tall allele from one parent and one short allele from the other parent will also have tall stems. Mendel's work found that alleles assort independently in the production of <a title="Gamete" href="http://en.wikipedia.org/wiki/Gamete">gametes</a>, or <a title="Germ cell" href="http://en.wikipedia.org/wiki/Germ_cell">germ cells</a>, ensuring variation in the next generation.</p>
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| − | <p>Prior to Mendel's work, the dominant theory of heredity was one of <a title="Blending inheritance" href="http://en.wikipedia.org/wiki/Blending_inheritance">blending inheritance</a>, which proposes that the traits of the parents blend or mix in a smooth, continuous gradient in the offspring. Although Mendel's work was largely unrecognized after its first publication in 1866, it was rediscovered in 1900 by three European scientists, <a title="Hugo de Vries" href="http://en.wikipedia.org/wiki/Hugo_de_Vries">Hugo de Vries</a>, <a title="Carl Correns" href="http://en.wikipedia.org/wiki/Carl_Correns">Carl Correns</a>, and <a title="Erich von Tschermak" href="http://en.wikipedia.org/wiki/Erich_von_Tschermak">Erich von Tschermak</a>, who had reached similar conclusions from their own research. However, these scientists were not yet aware of the identity of the 'discrete units' on which genetic material resides.</p>
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| − | <p>A series of subsequent discoveries led to the realization decades later that <a title="Chromosome" href="http://en.wikipedia.org/wiki/Chromosome">chromosomes</a> within <a title="Cell (biology)" href="http://en.wikipedia.org/wiki/Cell_%28biology%29">cells</a> are the carriers of genetic material, and that they are made of <a title="DNA" href="http://en.wikipedia.org/wiki/DNA">DNA</a> (deoxyribonucleic acid), a <a title="Polymer" href="http://en.wikipedia.org/wiki/Polymer">polymeric</a> molecule found in all cells on which the 'discrete units' of Mendelian inheritance are encoded. The modern study of <a title="Genetics" href="http://en.wikipedia.org/wiki/Genetics">genetics</a> at the level of DNA is known as <a title="Molecular genetics" href="http://en.wikipedia.org/wiki/Molecular_genetics">molecular genetics</a> and the synthesis of molecular genetics with traditional <a title="Charles Darwin" href="http://en.wikipedia.org/wiki/Charles_Darwin">Darwinian</a> <a title="Evolution" href="http://en.wikipedia.org/wiki/Evolution">evolution</a> is known as the <a title="Modern evolutionary synthesis" href="http://en.wikipedia.org/wiki/Modern_evolutionary_synthesis">modern evolutionary synthesis</a>.</p>
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| − | <p><a id="Physical_definitions" name="Physical_definitions"></a></p> | |
| − | <h2><span class="editsection">[<a title="Edit section: Physical definitions" href="http://en.wikipedia.org/w/index.php?title=Gene&action=edit&section=3">edit</a>]</span> <span class="mw-headline">Physical definitions</span></h2>
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| − | <div class="thumb tleft">
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| − | <div class="thumbinner" style="WIDTH: 302px"><a class="image" title="The chemical structure of a four-base fragment of a DNA double helix." href="http://en.wikipedia.org/wiki/Image:DNA_chemical_structure.svg"><img class="thumbimage" height="350" alt="The chemical structure of a four-base fragment of a DNA double helix." width="300" border="0" src="http://upload.wikimedia.org/wikipedia/commons/thumb/e/e4/DNA_chemical_structure.svg/300px-DNA_chemical_structure.svg.png" /></a>
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| − | <div class="thumbcaption">
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| − | <div class="magnify"><a class="internal" title="Enlarge" href="http://en.wikipedia.org/wiki/Image:DNA_chemical_structure.svg"><img height="11" alt="" width="15" src="http://en.wikipedia.org/skins-1.5/common/images/magnify-clip.png" /></a></div>
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| − | The chemical structure of a four-base fragment of a DNA double helix.</div>
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| − | </div>
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| − | </div>
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| − | <p>The vast majority of living organisms encode their genes in long strands of <a title="DNA" href="http://en.wikipedia.org/wiki/DNA">DNA</a>. DNA consists of a chain made from four types of <a title="Nucleotide" href="http://en.wikipedia.org/wiki/Nucleotide">nucleotide</a> subunits: <a title="Adenine" href="http://en.wikipedia.org/wiki/Adenine">adenine</a>, <a title="Cytosine" href="http://en.wikipedia.org/wiki/Cytosine">cytosine</a>, <a title="Guanine" href="http://en.wikipedia.org/wiki/Guanine">guanine</a>, and <a title="Thymine" href="http://en.wikipedia.org/wiki/Thymine">thymine</a>. Each nucleotide subunit consists of three components: a <a title="Phosphate" href="http://en.wikipedia.org/wiki/Phosphate">phosphate</a> group, a <a title="Deoxyribose" href="http://en.wikipedia.org/wiki/Deoxyribose">deoxyribose</a> sugar ring, and a <a title="Nucleobase" href="http://en.wikipedia.org/wiki/Nucleobase">nucleobase</a>. Thus, nucleotides in DNA or RNA are typically called 'bases'; consequently they are commonly referred to simply by their <a title="Purine" href="http://en.wikipedia.org/wiki/Purine">purine</a> or <a title="Pyrimidine" href="http://en.wikipedia.org/wiki/Pyrimidine">pyrimidine</a> original base components adenine, cytosine, guanine, thymine. Adenine and guanine are purines and cytosine and thymine are pyrimidines. The most common form of DNA in a cell is in a <a title="Double helix" href="http://en.wikipedia.org/wiki/Double_helix">double helix</a> structure, in which two individual DNA strands twist around each other in a right-handed spiral. In this structure, the <a class="mw-redirect" title="Watson-Crick base pair" href="http://en.wikipedia.org/wiki/Watson-Crick_base_pair">base pairing</a> rules specify that <a title="Guanine" href="http://en.wikipedia.org/wiki/Guanine">guanine</a> pairs with <a title="Cytosine" href="http://en.wikipedia.org/wiki/Cytosine">cytosine</a> and <a title="Adenine" href="http://en.wikipedia.org/wiki/Adenine">adenine</a> pairs with <a title="Thymine" href="http://en.wikipedia.org/wiki/Thymine">thymine</a> (each pair contains one purine and one pyrimidine). The base pairing between guanine and cytosine forms three hydrogen bonds, while the base pairing between adenine and thymine forms two hydrogen bonds. The two strands in a double helix must therefore be <em>complementary</em>, that is, their bases must align such that the adenines of one strand are paired with the thymines of the other strand, and so on.</p>
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| − | <p>Due to the chemical composition of the pentose residues of the bases, DNA strands have directionality. One end of a DNA polymer contains an exposed <a title="Hydroxyl" href="http://en.wikipedia.org/wiki/Hydroxyl">hydroxyl</a> group on the <a title="Deoxyribose" href="http://en.wikipedia.org/wiki/Deoxyribose">deoxyribose</a>, this is known as the <a class="mw-redirect" title="3' end" href="http://en.wikipedia.org/wiki/3%27_end">3' end</a> of the molecule. The other end contains an exposed <a title="Phosphate" href="http://en.wikipedia.org/wiki/Phosphate">phosphate</a> group, this is the <a class="mw-redirect" title="5' end" href="http://en.wikipedia.org/wiki/5%27_end">5' end</a>. The directionality of DNA is vitally important to many cellular processes, since double helices are necessarily directional (a strand running 5'-3' pairs with a complementary strand running 3'-5') and processes such as <a title="DNA replication" href="http://en.wikipedia.org/wiki/DNA_replication">DNA replication</a> occur in only one direction. All nucleic acid synthesis in a cell occurs in the 5'-3' direction, because new monomers are added via a <a title="Dehydration" href="http://en.wikipedia.org/wiki/Dehydration">dehydration</a> reaction that uses the exposed 3' hydroxyl as a <a title="Nucleophile" href="http://en.wikipedia.org/wiki/Nucleophile">nucleophile</a>.</p>
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| − | <p>The <a title="Gene expression" href="http://en.wikipedia.org/wiki/Gene_expression">expression</a> of genes encoded in DNA begins by <a title="Transcription (genetics)" href="http://en.wikipedia.org/wiki/Transcription_%28genetics%29">transcribing</a> the gene into <a title="RNA" href="http://en.wikipedia.org/wiki/RNA">RNA</a>, a second type of <a title="Nucleic acid" href="http://en.wikipedia.org/wiki/Nucleic_acid">nucleic acid</a> that is very similar to DNA, but whose monomers contain the sugar <a title="Ribose" href="http://en.wikipedia.org/wiki/Ribose">ribose</a> rather than <a title="Deoxyribose" href="http://en.wikipedia.org/wiki/Deoxyribose">deoxyribose</a>. RNA also contains the base <a title="Uracil" href="http://en.wikipedia.org/wiki/Uracil">uracil</a> in place of <a title="Thymine" href="http://en.wikipedia.org/wiki/Thymine">thymine</a>. RNA molecules are less stable than DNA and are typically single-stranded. Genes that encode <a title="Protein" href="http://en.wikipedia.org/wiki/Protein">proteins</a> are composed of a series of three-<a title="Nucleotide" href="http://en.wikipedia.org/wiki/Nucleotide">nucleotide</a> sequences called <a class="mw-redirect" title="Codon" href="http://en.wikipedia.org/wiki/Codon">codons</a>, which serve as the "words" in the genetic "language". The <a title="Genetic code" href="http://en.wikipedia.org/wiki/Genetic_code">genetic code</a> specifies the correspondence during <a class="mw-redirect" title="Translation (genetics)" href="http://en.wikipedia.org/wiki/Translation_%28genetics%29">protein translation</a> between codons and <a title="Amino acid" href="http://en.wikipedia.org/wiki/Amino_acid">amino acids</a>. The genetic code is nearly the same for all known organisms.</p>
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| − | <p><a id="RNA_genes" name="RNA_genes"></a></p>
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| − | <h3><span class="editsection">[<a title="Edit section: RNA genes" href="http://en.wikipedia.org/w/index.php?title=Gene&action=edit&section=4">edit</a>]</span> <span class="mw-headline">RNA genes</span></h3>
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| − | <p>In some cases, <a title="RNA" href="http://en.wikipedia.org/wiki/RNA">RNA</a> is an intermediate product in the process of manufacturing proteins from genes. However, for other gene sequences, the RNA molecules are the actual functional products. For example, RNAs known as <a title="Ribozyme" href="http://en.wikipedia.org/wiki/Ribozyme">ribozymes</a> are capable of <a title="Enzyme" href="http://en.wikipedia.org/wiki/Enzyme">enzymatic function</a>, and <a title="MicroRNA" href="http://en.wikipedia.org/wiki/MicroRNA">miRNAs</a> have a regulatory role. The <a title="DNA" href="http://en.wikipedia.org/wiki/DNA">DNA</a> sequences from which such RNAs are transcribed are known as <a class="mw-redirect" title="Non-coding DNA" href="http://en.wikipedia.org/wiki/Non-coding_DNA">non-coding DNA</a>, or <a class="mw-redirect" title="RNA gene" href="http://en.wikipedia.org/wiki/RNA_gene">RNA genes</a>.</p>
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| − | <p>Some <a title="Virus" href="http://en.wikipedia.org/wiki/Virus">viruses</a> store their entire genomes in the form of RNA, and contain no DNA at all. Because they use RNA to store genes, their <a title="Cell (biology)" href="http://en.wikipedia.org/wiki/Cell_%28biology%29">cellular</a> <a title="Host (biology)" href="http://en.wikipedia.org/wiki/Host_%28biology%29">hosts</a> may synthesize their proteins as soon as they are <a title="Infection" href="http://en.wikipedia.org/wiki/Infection">infected</a> and without the delay in waiting for transcription. On the other hand, RNA <a title="Retrovirus" href="http://en.wikipedia.org/wiki/Retrovirus">retroviruses</a>, such as <a title="HIV" href="http://en.wikipedia.org/wiki/HIV">HIV</a>, require the <a title="Reverse transcription" href="http://en.wikipedia.org/wiki/Reverse_transcription">reverse transcription</a> of their <a title="Genome" href="http://en.wikipedia.org/wiki/Genome">genome</a> from RNA into DNA before their proteins can be synthesized. In 2006, French researchers came across a puzzling example of RNA-mediated inheritance in mouse. Mice with a <a title="Mutation" href="http://en.wikipedia.org/wiki/Mutation#By_effect_on_function">loss-of-function mutation</a> in the gene Kit have white tails. Offspring of these mutants can have white tails despite having only normal Kit genes. The research team traced this effect back to mutated Kit RNA.<sup class="reference" id="_ref-rass_0"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-rass">[14]</a></sup> While RNA is common as genetic storage material in viruses, in mammals in particular RNA inheritance has been observed very rarely.</p>
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| − | <p><a id="Functional_structure_of_a_gene" name="Functional_structure_of_a_gene"></a></p>
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| − | <h3><span class="editsection">[<a title="Edit section: Functional structure of a gene" href="http://en.wikipedia.org/w/index.php?title=Gene&action=edit&section=5">edit</a>]</span> <span class="mw-headline">Functional structure of a gene</span></h3>
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| − | <div class="thumb tright">
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| − | <div class="thumbinner" style="WIDTH: 402px"><a class="image" title="Diagram of the "typical" eukaryotic protein-coding gene. Promoters and enhancers determine what portions of the DNA will be transcribed into the precursor mRNA (pre-mRNA). The pre-mRNA is then spliced into messenger RNA (mRNA) which is later translated into protein." href="http://en.wikipedia.org/wiki/Image:Gene2-plain.svg"><img class="thumbimage" height="339" alt="Diagram of the "typical" eukaryotic protein-coding gene. Promoters and enhancers determine what portions of the DNA will be transcribed into the precursor mRNA (pre-mRNA). The pre-mRNA is then spliced into messenger RNA (mRNA) which is later translated into protein." width="400" border="0" src="http://upload.wikimedia.org/wikipedia/commons/thumb/a/a7/Gene2-plain.svg/400px-Gene2-plain.svg.png" /></a>
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| − | <div class="thumbcaption">
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| − | <div class="magnify"><a class="internal" title="Enlarge" href="http://en.wikipedia.org/wiki/Image:Gene2-plain.svg"><img height="11" alt="" width="15" src="http://en.wikipedia.org/skins-1.5/common/images/magnify-clip.png" /></a></div>
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| − | Diagram of the "typical" <a title="Eukaryote" href="http://en.wikipedia.org/wiki/Eukaryote">eukaryotic</a> protein-coding <strong>gene</strong>. <a title="Promoter" href="http://en.wikipedia.org/wiki/Promoter">Promoters</a> and <a title="Enhancer" href="http://en.wikipedia.org/wiki/Enhancer">enhancers</a> determine what portions of the <a title="DNA" href="http://en.wikipedia.org/wiki/DNA">DNA</a> will be <a title="Transcription (genetics)" href="http://en.wikipedia.org/wiki/Transcription_%28genetics%29">transcribed</a> into the <a title="Precursor mRNA" href="http://en.wikipedia.org/wiki/Precursor_mRNA">precursor mRNA</a> (pre-mRNA). The pre-mRNA is then spliced into <a title="Messenger RNA" href="http://en.wikipedia.org/wiki/Messenger_RNA">messenger RNA</a> (mRNA) which is later <a title="Translation (biology)" href="http://en.wikipedia.org/wiki/Translation_%28biology%29">translated</a> into <a title="Protein" href="http://en.wikipedia.org/wiki/Protein">protein</a>.</div>
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| − | </div>
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| − | </div>
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| − | <p>All genes have regulatory regions in addition to regions that explicitly code for a protein or RNA product. A regulatory region shared by almost all genes is known as the <a title="Promoter" href="http://en.wikipedia.org/wiki/Promoter">promoter</a>, which provides a position that is recognized by the transcription machinery when a gene is about to be transcribed and expressed. Although promoter regions have a <a title="Consensus sequence" href="http://en.wikipedia.org/wiki/Consensus_sequence">consensus sequence</a> that is the most common sequence at this position, some genes have "strong" promoters that bind the transcription machinery well, and others have "weak" promoters that bind poorly. These weak promoters usually permit a lower rate of transcription than the strong promoters, because the transcription machinery binds to them and initiates transcription less frequently. Other possible regulatory regions include <a title="Enhancer (genetics)" href="http://en.wikipedia.org/wiki/Enhancer_%28genetics%29">enhancers</a>, which can compensate for a weak promoter. Most regulatory regions are "upstream" — that is, before or toward the 5' end of the transcription initiation site. <a class="mw-redirect" title="Eukaryotic" href="http://en.wikipedia.org/wiki/Eukaryotic">Eukaryotic</a> <a title="Promoter" href="http://en.wikipedia.org/wiki/Promoter">promoter</a> regions are much more complex and difficult to identify than <a class="mw-redirect" title="Prokaryotic" href="http://en.wikipedia.org/wiki/Prokaryotic">prokaryotic</a> promoters.</p>
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| − | <p>Many prokaryotic genes are organized into <a title="Operon" href="http://en.wikipedia.org/wiki/Operon">operons</a>, or groups of genes whose products have related functions and which are transcribed as a unit. By contrast, <a title="Eukaryotic gene example" href="http://en.wikipedia.org/wiki/Eukaryotic_gene_example">eukaryotic genes</a> are transcribed only one at a time, but may include long stretches of DNA called <a title="Intron" href="http://en.wikipedia.org/wiki/Intron">introns</a> which are transcribed but never translated into protein (they are spliced out before translation). Splicing can also occur in prokaryotic genes, but is less common than in eukaryotes.<sup class="reference" id="_ref-1"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-1">[15]</a></sup></p>
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| − | <p><a id="Chromosomes" name="Chromosomes"></a></p>
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| − | <h3><span class="editsection">[<a title="Edit section: Chromosomes" href="http://en.wikipedia.org/w/index.php?title=Gene&action=edit&section=6">edit</a>]</span> <span class="mw-headline">Chromosomes</span></h3>
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| − | <p>The total complement of genes in an organism or cell is known as its <a title="Genome" href="http://en.wikipedia.org/wiki/Genome">genome</a>, which may be stored on one or more <a title="Chromosome" href="http://en.wikipedia.org/wiki/Chromosome">chromosomes</a>; the region of the chromosome at which a particular gene is located is called its <a title="Locus (genetics)" href="http://en.wikipedia.org/wiki/Locus_%28genetics%29">locus</a>. A chromosome consists of a single, very long DNA helix on which thousands of genes are encoded. <a title="Prokaryote" href="http://en.wikipedia.org/wiki/Prokaryote">Prokaryotes</a> - <a title="Bacteria" href="http://en.wikipedia.org/wiki/Bacteria">bacteria</a> and <a title="Archaea" href="http://en.wikipedia.org/wiki/Archaea">archaea</a> - typically store their genomes on a single large, circular chromosome, sometimes supplemented by additional small circles of DNA called <a title="Plasmid" href="http://en.wikipedia.org/wiki/Plasmid">plasmids</a>, which usually encode only a few genes and are easily transferable between individuals. For example, the genes for <a title="Antibiotic resistance" href="http://en.wikipedia.org/wiki/Antibiotic_resistance">antibiotic resistance</a> are usually encoded on bacterial plasmids and can be passed between individual cells, even those of different species, via <a title="Horizontal gene transfer" href="http://en.wikipedia.org/wiki/Horizontal_gene_transfer">horizontal gene transfer</a>. Although some simple eukaryotes also possess plasmids with small numbers of genes, the majority of eukaryotic genes are stored on multiple linear chromosomes, which are packed within the <a title="Cell nucleus" href="http://en.wikipedia.org/wiki/Cell_nucleus">nucleus</a> in complex with storage proteins called <a title="Histone" href="http://en.wikipedia.org/wiki/Histone">histones</a>. The manner in which DNA is stored on the histone, as well as chemical modifications of the histone itself, are regulatory mechanisms governing whether a particular region of DNA is accessible for <a title="Gene expression" href="http://en.wikipedia.org/wiki/Gene_expression">gene expression</a>. The ends of eukaryotic chromosomes are capped by long stretches of repetitive sequences called <a title="Telomere" href="http://en.wikipedia.org/wiki/Telomere">telomeres</a>, which do not code for any gene product but are present to prevent degradation of coding and regulatory regions during <a title="DNA replication" href="http://en.wikipedia.org/wiki/DNA_replication">DNA replication</a>. The length of the telomeres tends to decrease each time the genome is replicated in preparation for cell division; the loss of telomeres has been proposed as an explanation for cellular <a title="Senescence" href="http://en.wikipedia.org/wiki/Senescence">senescence</a>, or the loss of the ability to divide, and by extension for the <a class="mw-redirect" title="Aging" href="http://en.wikipedia.org/wiki/Aging">aging</a> process in organisms.<sup class="reference" id="_ref-Braig_0"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-Braig">[16]</a></sup></p>
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| − | <p>While the chromosomes of prokaryotes are relatively gene-dense, those of eukaryotes often contain so-called "<a title="Junk DNA" href="http://en.wikipedia.org/wiki/Junk_DNA">junk DNA</a>", or regions of DNA that serve no obvious function. Simple single-celled eukaryotes have relatively small amounts of such DNA, while the genomes of complex multicellular organisms, including humans, contain an absolute majority of DNA without an identified function.<sup class="reference" id="_ref-IHSGC2004_1"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-IHSGC2004">[6]</a></sup> However it now appears that, although protein-coding DNA makes up barely 2% of the human genome, about 80% of the bases in the genome may be being expressed, so the term "junk DNA" may be a misnomer.<sup class="reference" id="_ref-Rethink_1"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-Rethink">[2]</a></sup></p>
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| − | <p><a id="Gene_expression" name="Gene_expression"></a></p>
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| − | <h2><span class="editsection">[<a title="Edit section: Gene expression" href="http://en.wikipedia.org/w/index.php?title=Gene&action=edit&section=7">edit</a>]</span> <span class="mw-headline">Gene expression</span></h2>
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| − | <dl><dd>
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| − | <div class="noprint relarticle mainarticle"><em>Main article: <a title="Gene expression" href="http://en.wikipedia.org/wiki/Gene_expression">Gene expression</a></em></div>
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| − | </dd></dl>
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| − | <p>In all organisms, there are two major steps separating a protein-coding gene from its protein: first, the DNA on which the gene resides must be <em><a title="Transcription (genetics)" href="http://en.wikipedia.org/wiki/Transcription_%28genetics%29">transcribed</a></em> from DNA to <a title="Messenger RNA" href="http://en.wikipedia.org/wiki/Messenger_RNA">messenger RNA</a> (mRNA), and second, it must be <em><a class="mw-redirect" title="Translation (genetics)" href="http://en.wikipedia.org/wiki/Translation_%28genetics%29">translated</a></em> from mRNA to protein. RNA-coding genes must still go through the first step, but are not translated into protein. The process of producing a biologically functional molecule of either RNA or protein is called <a title="Gene expression" href="http://en.wikipedia.org/wiki/Gene_expression">gene expression</a>, and the resulting molecule itself is called a <a title="Gene product" href="http://en.wikipedia.org/wiki/Gene_product">gene product</a>.</p>
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| − | <p><a id="Genetic_code" name="Genetic_code"></a></p>
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| − | <h3><span class="editsection">[<a title="Edit section: Genetic code" href="http://en.wikipedia.org/w/index.php?title=Gene&action=edit&section=8">edit</a>]</span> <span class="mw-headline">Genetic code</span></h3>
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| − | <div class="thumb tright">
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| − | <div class="thumbinner" style="WIDTH: 202px"><a class="image" title="Schematic diagram of a single-stranded RNA molecule illustrating the position of three-base codons." href="http://en.wikipedia.org/wiki/Image:Rna-codons-protein.png"><img class="thumbimage" height="259" alt="Schematic diagram of a single-stranded RNA molecule illustrating the position of three-base codons." width="200" border="0" src="http://upload.wikimedia.org/wikipedia/en/thumb/1/1d/Rna-codons-protein.png/200px-Rna-codons-protein.png" /></a>
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| − | <div class="thumbcaption">
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| − | <div class="magnify"><a class="internal" title="Enlarge" href="http://en.wikipedia.org/wiki/Image:Rna-codons-protein.png"><img height="11" alt="" width="15" src="http://en.wikipedia.org/skins-1.5/common/images/magnify-clip.png" /></a></div>
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| − | Schematic diagram of a single-stranded RNA molecule illustrating the position of three-base codons.</div>
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| − | </div>
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| − | </div>
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| − | <dl><dd>
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| − | <div class="noprint relarticle mainarticle"><em>Main article: <a title="Genetic code" href="http://en.wikipedia.org/wiki/Genetic_code">Genetic code</a></em></div>
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| − | </dd></dl>
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| − | <p>The genetic code is the set of rules by which a gene is translated into a functional protein. Each gene consists of a specific sequence of nucleotides encoded in a DNA (or sometimes RNA) strand; a correspondence between nucleotides, the basic building blocks of genetic material, and amino acids, the basic building blocks of proteins, must be established for genes to be successfully translated into functional proteins. Sets of three nucleotides, known as <a class="mw-redirect" title="Codon" href="http://en.wikipedia.org/wiki/Codon">codons</a>, each correspond to a specific amino acid or to a signal; three codons are known as "stop codons" and, instead of specifying a new amino acid, alert the translation machinery that the end of the gene has been reached. There are 64 possible codons (four possible nucleotides at each of three positions, hence 4<sup>3</sup> possible codons) and only 20 standard amino acids; hence the code is redundant and multiple codons can specify the same amino acid. The correspondence between codons and amino acids is nearly universal among all known living organisms.</p>
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| − | <p><a id="Transcription" name="Transcription"></a></p>
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| − | <h3><span class="mw-headline">Transcription</span></h3>
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| − | <p>The process of genetic <a title="Transcription (genetics)" href="http://en.wikipedia.org/wiki/Transcription_%28genetics%29">transcription</a> produces a single-stranded <a title="RNA" href="http://en.wikipedia.org/wiki/RNA">RNA</a> molecule known as <a title="Messenger RNA" href="http://en.wikipedia.org/wiki/Messenger_RNA">messenger RNA</a>, whose nucleotide sequence is complementary to the DNA from which it was transcribed. The DNA strand whose sequence matches that of the RNA is known as the <a title="Coding strand" href="http://en.wikipedia.org/wiki/Coding_strand">coding strand</a> and the strand from which the RNA was synthesized is the <a class="mw-redirect" title="Template strand" href="http://en.wikipedia.org/wiki/Template_strand">template strand</a>. Transcription is performed by an <a title="Enzyme" href="http://en.wikipedia.org/wiki/Enzyme">enzyme</a> called an <a title="RNA polymerase" href="http://en.wikipedia.org/wiki/RNA_polymerase">RNA polymerase</a>, which reads the template strand in the <a class="mw-redirect" title="3' end" href="http://en.wikipedia.org/wiki/3%27_end">3'</a> to <a class="mw-redirect" title="5' end" href="http://en.wikipedia.org/wiki/5%27_end">5'</a> direction and synthesizes the RNA from <a class="mw-redirect" title="5' end" href="http://en.wikipedia.org/wiki/5%27_end">5'</a> to <a class="mw-redirect" title="3' end" href="http://en.wikipedia.org/wiki/3%27_end">3'</a>. To initiate transcription, the polymerase first recognizes and binds a <a title="Promoter" href="http://en.wikipedia.org/wiki/Promoter">promoter</a> region of the gene. Thus a major mechanism of <a class="mw-redirect" title="Gene regulation" href="http://en.wikipedia.org/wiki/Gene_regulation">gene regulation</a> is the blocking or sequestering of the promoter region, either by tight binding by <a title="Repressor" href="http://en.wikipedia.org/wiki/Repressor">repressor</a> molecules that physically block the polymerase, or by organizing the DNA so that the promoter region is not accessible.</p>
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| − | <p>In <a title="Prokaryote" href="http://en.wikipedia.org/wiki/Prokaryote">prokaryotes</a>, transcription occurs in the <a title="Cytoplasm" href="http://en.wikipedia.org/wiki/Cytoplasm">cytoplasm</a>; for very long transcripts, translation may begin at the 5' end of the RNA while the 3' end is still being transcribed. In <a title="Eukaryote" href="http://en.wikipedia.org/wiki/Eukaryote">eukaryotes</a>, transcription necessarily occurs in the nucleus, where the cell's DNA is sequestered; the RNA molecule produced by the polymerase is known as the <a class="mw-redirect" title="Primary transcript" href="http://en.wikipedia.org/wiki/Primary_transcript">primary transcript</a> and must undergo <a title="Post-transcriptional modification" href="http://en.wikipedia.org/wiki/Post-transcriptional_modification">post-transcriptional modifications</a> before being exported to the cytoplasm for translation. The <a title="Splicing (genetics)" href="http://en.wikipedia.org/wiki/Splicing_%28genetics%29">splicing</a> of <a title="Intron" href="http://en.wikipedia.org/wiki/Intron">introns</a> present within the transcribed region is a modification unique to eukaryotes; <a title="Alternative splicing" href="http://en.wikipedia.org/wiki/Alternative_splicing">alternative splicing</a> mechanisms can result in mature transcripts from the same gene having different sequences and thus coding for different proteins. This is a major form of regulation in eukaryotic cells.</p>
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| − | <p><a id="Translation" name="Translation"></a></p>
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| − | <h3><span class="editsection">[<a title="Edit section: Translation" href="http://en.wikipedia.org/w/index.php?title=Gene&action=edit&section=10">edit</a>]</span> <span class="mw-headline">Translation</span></h3>
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| − | <p><a class="mw-redirect" title="Translation (genetics)" href="http://en.wikipedia.org/wiki/Translation_%28genetics%29">Translation</a> is the process by which a mature mRNA molecule is used as a template for synthesizing a new <a title="Protein" href="http://en.wikipedia.org/wiki/Protein">protein</a>. Translation is carried out by <a title="Ribosome" href="http://en.wikipedia.org/wiki/Ribosome">ribosomes</a>, large complexes of RNA and protein responsible for carrying out the chemical reactions to add new <a title="Amino acid" href="http://en.wikipedia.org/wiki/Amino_acid">amino acids</a> to a growing <a class="mw-redirect" title="Polypeptide chain" href="http://en.wikipedia.org/wiki/Polypeptide_chain">polypeptide chain</a> by the formation of <a title="Peptide bond" href="http://en.wikipedia.org/wiki/Peptide_bond">peptide bonds</a>. The genetic code is read three nucleotides at a time, in units called <a class="mw-redirect" title="Codon" href="http://en.wikipedia.org/wiki/Codon">codons</a>, via interactions with specialized RNA molecules called <a title="Transfer RNA" href="http://en.wikipedia.org/wiki/Transfer_RNA">transfer RNA</a> (tRNA). Each tRNA has three unpaired bases known as the <a class="mw-redirect" title="Anticodon" href="http://en.wikipedia.org/wiki/Anticodon">anticodon</a> that are complementary to the codon it reads; the tRNA is also <a class="mw-redirect" title="Covalent" href="http://en.wikipedia.org/wiki/Covalent">covalently</a> attached to the <a title="Amino acid" href="http://en.wikipedia.org/wiki/Amino_acid">amino acid</a> specified by the complementary codon. When the tRNA binds to its complementary codon in an mRNA strand, the ribosome ligates its amino acid cargo to the new polypeptide chain, which is synthesized from <a title="N-terminus" href="http://en.wikipedia.org/wiki/N-terminus">amino terminus</a> to <a title="C-terminus" href="http://en.wikipedia.org/wiki/C-terminus">carboxyl terminus</a>. During and after its synthesis, the new protein must <a title="Protein folding" href="http://en.wikipedia.org/wiki/Protein_folding">fold</a> to its active <a title="Tertiary structure" href="http://en.wikipedia.org/wiki/Tertiary_structure">three-dimensional structure</a> before it can carry out its cellular function.</p>
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| − | <p><a id="DNA_replication_and_inheritance" name="DNA_replication_and_inheritance"></a></p>
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| − | <h2><span class="mw-headline">DNA replication and inheritance</span></h2>
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| − | <p>The growth, development, and reproduction of organisms relies on <a title="Cell division" href="http://en.wikipedia.org/wiki/Cell_division">cell division</a>, or the process by which a single <a title="Cell (biology)" href="http://en.wikipedia.org/wiki/Cell_%28biology%29">cell</a> divides into two usually identical <a class="mw-redirect" title="Daughter cell" href="http://en.wikipedia.org/wiki/Daughter_cell">daughter cells</a>. This requires first making a duplicate copy of every gene in the <a title="Genome" href="http://en.wikipedia.org/wiki/Genome">genome</a> in a process called <a title="DNA replication" href="http://en.wikipedia.org/wiki/DNA_replication">DNA replication</a>. The copies are made by specialized <a title="Enzyme" href="http://en.wikipedia.org/wiki/Enzyme">enzymes</a> known as <a title="DNA polymerase" href="http://en.wikipedia.org/wiki/DNA_polymerase">DNA polymerases</a>, which "read" one strand of the double-helical DNA, known as the template strand, and synthesize a new complementary strand. Because the DNA double helix is held together by <a title="Base pair" href="http://en.wikipedia.org/wiki/Base_pair">base pairing</a>, the sequence of one strand completely specifies the sequence of its complement; hence only one strand needs to be read by the enzyme to produce a faithful copy. The process of DNA replication is <a title="Semiconservative replication" href="http://en.wikipedia.org/wiki/Semiconservative_replication">semiconservative</a>; that is, the copy of the genome inherited by each daughter cell contains one original and one newly synthesized strand of DNA.<sup class="reference" id="_ref-Watson_2004_1"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-Watson_2004">[8]</a></sup></p>
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| − | <p>After DNA replication is complete, the cell must physically separate the two copies of the genome and divide into two distinct membrane-bound cells. In <a title="Prokaryote" href="http://en.wikipedia.org/wiki/Prokaryote">prokaryotes</a> - <a title="Bacteria" href="http://en.wikipedia.org/wiki/Bacteria">bacteria</a> and <a title="Archaea" href="http://en.wikipedia.org/wiki/Archaea">archaea</a> - this usually occurs via a relatively simple process called <a title="Binary fission" href="http://en.wikipedia.org/wiki/Binary_fission">binary fission</a>, in which each circular genome attaches to the <a title="Cell membrane" href="http://en.wikipedia.org/wiki/Cell_membrane">cell membrane</a> and is separated into the daughter cells as the membrane <a class="mw-redirect" title="Invaginate" href="http://en.wikipedia.org/wiki/Invaginate">invaginates</a> to split the <a title="Cytoplasm" href="http://en.wikipedia.org/wiki/Cytoplasm">cytoplasm</a> into two membrane-bound portions. Binary fission is extremely fast compared to the rates of cell division in <a title="Eukaryote" href="http://en.wikipedia.org/wiki/Eukaryote">eukaryotes</a>. Eukaryotic cell division is a more complex process known as the <a title="Cell cycle" href="http://en.wikipedia.org/wiki/Cell_cycle">cell cycle</a>; DNA replication occurs during a phase of this cycle known as <a title="S phase" href="http://en.wikipedia.org/wiki/S_phase">S phase</a>, while the process of segregating <a title="Chromosome" href="http://en.wikipedia.org/wiki/Chromosome">chromosomes</a> and splitting the <a title="Cytoplasm" href="http://en.wikipedia.org/wiki/Cytoplasm">cytoplasm</a> occurs during <a class="mw-redirect" title="M phase" href="http://en.wikipedia.org/wiki/M_phase">M phase</a>. In many single-celled eukaryotes such as <a title="Yeast" href="http://en.wikipedia.org/wiki/Yeast">yeast</a>, reproduction by <a title="Budding" href="http://en.wikipedia.org/wiki/Budding">budding</a> is common, which results in asymmetrical portions of cytoplasm in the two daughter cells.</p>
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| − | <p><a id="Molecular_inheritance" name="Molecular_inheritance"></a></p>
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| − | <h3><span class="editsection">[<a title="Edit section: Molecular inheritance" href="http://en.wikipedia.org/w/index.php?title=Gene&action=edit&section=12">edit</a>]</span> <span class="mw-headline">Molecular inheritance</span></h3>
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| − | <p>The duplication and transmission of genetic material from one generation of cells to the next is the basis for molecular inheritance, and the link between the classical and molecular pictures of genes. Organisms inherit the characteristics of their parents because the cells of the offspring contain copies of the genes in their parents' cells. In <a title="Asexual reproduction" href="http://en.wikipedia.org/wiki/Asexual_reproduction">asexually reproducing</a> organisms, the offspring will be a genetic copy or <a class="mw-redirect" title="Clone (genetics)" href="http://en.wikipedia.org/wiki/Clone_%28genetics%29">clone</a> of the parent organism. In <a title="Sexual reproduction" href="http://en.wikipedia.org/wiki/Sexual_reproduction">sexually reproducing</a> organisms, a specialized form of cell division called <a title="Meiosis" href="http://en.wikipedia.org/wiki/Meiosis">meiosis</a> produces cells called <a title="Gamete" href="http://en.wikipedia.org/wiki/Gamete">gametes</a> or <a title="Germ cell" href="http://en.wikipedia.org/wiki/Germ_cell">germ cells</a> that are <a class="mw-redirect" title="Haploid" href="http://en.wikipedia.org/wiki/Haploid">haploid</a>, or contain only one copy of each gene. The gametes produced by females are called <a title="Egg (biology)" href="http://en.wikipedia.org/wiki/Egg_%28biology%29">eggs</a> or ova, and those produced by males are called <a title="Sperm" href="http://en.wikipedia.org/wiki/Sperm">sperm</a>. Two gametes fuse to form a <a class="mw-redirect" title="Fertilized egg" href="http://en.wikipedia.org/wiki/Fertilized_egg">fertilized egg</a>, a single cell that once again has a <a class="mw-redirect" title="Diploid" href="http://en.wikipedia.org/wiki/Diploid">diploid</a> number of genes - each with one copy from the mother and one copy from the father.</p>
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| − | <p>During the process of meiotic cell division, an event called <a title="Genetic recombination" href="http://en.wikipedia.org/wiki/Genetic_recombination">genetic recombination</a> or <em>crossing-over</em> can sometimes occur, in which a length of DNA on one <a title="Chromatid" href="http://en.wikipedia.org/wiki/Chromatid">chromatid</a> is swapped with a length of DNA on the corresponding sister chromatid. This has no effect if the <a title="Allele" href="http://en.wikipedia.org/wiki/Allele">alleles</a> on the chromatids are the same, but results in reassortment of otherwise linked alleles if they are different. The Mendelian principle of independent assortment asserts that each of a parent's two genes for each trait will sort independently into gametes; which allele an organism inherits for one trait is unrelated to which allele it inherits for another trait. This is in fact only true for genes that do not reside on the same chromosome, or are located very far from one another on the same chromosome. The closer two genes lie on the same chromosome, the more closely they will be associated in gametes and the more often they will appear together; genes that are very close are essentially never separated because it is extremely unlikely that a crossover point will occur between them. This is known as <a title="Genetic linkage" href="http://en.wikipedia.org/wiki/Genetic_linkage">genetic linkage</a>.</p>
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| − | <p><a id="Mutation" name="Mutation"></a></p>
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| − | <h3><span class="editsection">[<a title="Edit section: Mutation" href="http://en.wikipedia.org/w/index.php?title=Gene&action=edit&section=13">edit</a>]</span> <span class="mw-headline">Mutation</span></h3>
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| − | <dl><dd>
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| − | <div class="noprint relarticle mainarticle"><em>Main article: <a title="Mutation" href="http://en.wikipedia.org/wiki/Mutation">Mutation</a></em></div>
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| − | </dd></dl>
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| − | <p>DNA replication is for the most part extremely accurate, with an error rate per site of around 10<sup>-6</sup> to 10<sup>-10</sup> in <a title="Eukaryote" href="http://en.wikipedia.org/wiki/Eukaryote">eukaryotes</a>.<sup class="reference" id="_ref-Watson_2004_2"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-Watson_2004">[8]</a></sup> Rare, spontaneous alterations in the base sequence of a particular gene arise from a number of sources, such as errors in <a title="DNA replication" href="http://en.wikipedia.org/wiki/DNA_replication">DNA replication</a> and the aftermath of <a class="mw-redirect" title="DNA damage" href="http://en.wikipedia.org/wiki/DNA_damage">DNA damage</a>. These errors are called <a title="Mutation" href="http://en.wikipedia.org/wiki/Mutation">mutations</a>. The cell contains many <a title="DNA repair" href="http://en.wikipedia.org/wiki/DNA_repair">DNA repair</a> mechanisms for preventing mutations and maintaining the integrity of the genome; however, in some cases — such as breaks in both DNA strands of a chromosome — repairing the physical damage to the molecule is a higher priority than producing an exact copy. Due to the degeneracy of the genetic code, some mutations in protein-coding genes are <em>silent</em>, or produce no change in the amino acid sequence of the protein for which they code; for example, the codons <a class="mw-redirect" title="Codon" href="http://en.wikipedia.org/wiki/Codon">UCU</a> and <a class="mw-redirect" title="Codon" href="http://en.wikipedia.org/wiki/Codon">UUC</a> both code for <a title="Serine" href="http://en.wikipedia.org/wiki/Serine">serine</a>, so the U↔C mutation has no effect on the protein. Mutations that do have phenotypic effects are most often neutral or deleterious to the organism, but sometimes they confer benefits to the organism's <a title="Fitness (biology)" href="http://en.wikipedia.org/wiki/Fitness_%28biology%29">fitness</a>.</p>
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| − | <p>Mutations propagated to the next <a title="Generation" href="http://en.wikipedia.org/wiki/Generation">generation</a> lead to variations within a species' population. Variants of a single gene are known as <a title="Allele" href="http://en.wikipedia.org/wiki/Allele">alleles</a>, and differences in <a title="Allele" href="http://en.wikipedia.org/wiki/Allele">alleles</a> may give rise to differences in traits. Although it is rare for the variants in a single gene to have clearly distinguishable phenotypic effects, certain well-defined traits are in fact controlled by single genetic loci. A gene's most common allele is called the <a title="Wild type" href="http://en.wikipedia.org/wiki/Wild_type">wild type</a> allele, and rare alleles are called <a title="Mutant" href="http://en.wikipedia.org/wiki/Mutant">mutants</a>. However, this does not imply that the wild-type allele is the <a title="Ancestor" href="http://en.wikipedia.org/wiki/Ancestor">ancestor</a> from which the <a title="Mutant" href="http://en.wikipedia.org/wiki/Mutant">mutants</a> are descended.</p>
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| − | <p><a id="The_genome" name="The_genome"></a></p>
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| − | <h2><span class="editsection">[<a title="Edit section: The genome" href="http://en.wikipedia.org/w/index.php?title=Gene&action=edit&section=14">edit</a>]</span> <span class="mw-headline">The genome</span></h2>
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| − | <p><a id="Chromosomal_organization" name="Chromosomal_organization"></a></p>
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| − | <h3><span class="editsection">[<a title="Edit section: Chromosomal organization" href="http://en.wikipedia.org/w/index.php?title=Gene&action=edit&section=15">edit</a>]</span> <span class="mw-headline">Chromosomal organization</span></h3>
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| − | <p>The total complement of genes in an organism or cell is known as its <a title="Genome" href="http://en.wikipedia.org/wiki/Genome">genome</a>. In <a title="Prokaryote" href="http://en.wikipedia.org/wiki/Prokaryote">prokaryotes</a>, the vast majority of genes are located on a single chromosome of circular DNA, while <a title="Eukaryote" href="http://en.wikipedia.org/wiki/Eukaryote">eukaryotes</a> usually possess multiple individual linear DNA helices packed into dense DNA-protein complexes called <a title="Chromosome" href="http://en.wikipedia.org/wiki/Chromosome">chromosomes</a>. <a title="Extrachromosomal DNA" href="http://en.wikipedia.org/wiki/Extrachromosomal_DNA">Extrachromosomal DNA</a> is present in many prokaryotes and some simple eukaryotes as small, circular pieces of DNA called <a title="Plasmid" href="http://en.wikipedia.org/wiki/Plasmid">plasmids</a>, which usually contain only a few genes each. Generally, regulatory regions and junk DNA are considered to be part of an organism's genome, but structural regions such as <a title="Telomere" href="http://en.wikipedia.org/wiki/Telomere">telomeres</a> are not. The location (or <a title="Locus (genetics)" href="http://en.wikipedia.org/wiki/Locus_%28genetics%29">locus</a>) of a gene and the chromosome on which it is situated is in a sense arbitrary. Genes that appear together on the chromosomes of one species, such as humans, may appear on separate chromosomes in another species, such as <a title="Mouse" href="http://en.wikipedia.org/wiki/Mouse">mice</a>. Two genes positioned near one another on a chromosome may encode proteins that figure in the same cellular process or in completely unrelated processes. As an example of the former, many of the genes involved in <a title="Spermatogenesis" href="http://en.wikipedia.org/wiki/Spermatogenesis">spermatogenesis</a> reside together on the <a title="Sex-determination system" href="http://en.wikipedia.org/wiki/Sex-determination_system">Y chromosome</a>.</p>
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| − | <p>Many species carry more than one copy of their genome within each of their <a title="Somatic cell" href="http://en.wikipedia.org/wiki/Somatic_cell">somatic cells</a>. Cells or organisms with only one copy of each gene are called <a class="mw-redirect" title="Haploid" href="http://en.wikipedia.org/wiki/Haploid">haploid</a>; those with two copies are called <a class="mw-redirect" title="Diploid" href="http://en.wikipedia.org/wiki/Diploid">diploid</a>; and those with more than two copies are called <a class="mw-redirect" title="Polyploid" href="http://en.wikipedia.org/wiki/Polyploid">polyploid</a>. When more than one copy is present, the two copies are not necessarily identical; in sexually reproducing organisms, one copy is normally inherited from each parent. The copies may contain distinct DNA sequences encoding distinct alleles.</p>
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| − | <p><a id="Composition_of_the_genome" name="Composition_of_the_genome"></a></p>
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| − | <h3><span class="editsection">[<a title="Edit section: Composition of the genome" href="http://en.wikipedia.org/w/index.php?title=Gene&action=edit&section=16">edit</a>]</span> <span class="mw-headline">Composition of the genome</span></h3>
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| − | <table style="FLOAT: right; MARGIN: 0px 0px 1em 1em" class="wikitable">
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| − | <caption>Gene content of various organisms<sup class="reference" id="_ref-Watson_2004_3"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-Watson_2004">[8]</a></sup></caption>
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| − | <tbody>
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| − | <tr>
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| − | <th>Species</th>
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| − | <th>Number of genes</th>
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| − | </tr>
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| − | <tr>
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| − | <td><em><a title="Mycoplasma genitalium" href="http://en.wikipedia.org/wiki/Mycoplasma_genitalium">Mycoplasma genitalium</a></em></td>
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| − | <td>500</td>
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| − | </tr>
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| − | <tr>
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| − | <td><em><a title="Streptococcus pneumoniae" href="http://en.wikipedia.org/wiki/Streptococcus_pneumoniae">Streptococcus pneumoniae</a></em></td>
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| − | <td>2,300</td>
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| − | </tr>
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| − | <tr>
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| − | <td><em><a title="Escherichia coli" href="http://en.wikipedia.org/wiki/Escherichia_coli">Escherichia coli</a></em></td>
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| − | <td>4,400</td>
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| − | </tr>
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| − | <tr>
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| − | <td><em><a title="Saccharomyces cerevisiae" href="http://en.wikipedia.org/wiki/Saccharomyces_cerevisiae">Saccharomyces cerevisiae</a></em></td>
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| − | <td>5,800</td>
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| − | </tr>
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| − | <tr>
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| − | <td><em><a title="Drosophila melanogaster" href="http://en.wikipedia.org/wiki/Drosophila_melanogaster">Drosophila melanogaster</a></em></td>
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| − | <td>13,700</td>
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| − | </tr>
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| − | <tr>
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| − | <td><em><a title="Caenorhabditis elegans" href="http://en.wikipedia.org/wiki/Caenorhabditis_elegans">Caenorhabditis elegans</a></em></td>
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| − | <td>19,000</td>
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| − | </tr>
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| − | <tr>
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| − | <td><em><a class="mw-redirect" title="Homo sapiens" href="http://en.wikipedia.org/wiki/Homo_sapiens">Homo sapiens</a></em></td>
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| − | <td>20,500<sup class="reference" id="_ref-gene_count2007_1"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-gene_count2007">[7]</a></sup></td>
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| − | </tr>
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| − | <tr>
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| − | <td><em><a title="Sea urchin" href="http://en.wikipedia.org/wiki/Sea_urchin">Sea urchin</a></em></td>
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| − | <td>23,300</td>
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| − | </tr>
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| − | <tr>
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| − | <td><em><a title="Arabidopsis thaliana" href="http://en.wikipedia.org/wiki/Arabidopsis_thaliana">Arabidopsis thaliana</a></em></td>
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| − | <td>25,500</td>
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| − | </tr>
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| − | <tr>
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| − | <td><em><a class="mw-redirect" title="Mus musculus" href="http://en.wikipedia.org/wiki/Mus_musculus">Mus musculus</a></em></td>
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| − | <td>29,000</td>
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| − | </tr>
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| − | <tr>
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| − | <td><em><a class="mw-redirect" title="Oryza sativa" href="http://en.wikipedia.org/wiki/Oryza_sativa">Oryza sativa</a></em></td>
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| − | <td>50,000</td>
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| − | </tr>
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| − | </tbody>
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| − | </table>
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| − | <p>Typical numbers of genes and size of <a title="Genome" href="http://en.wikipedia.org/wiki/Genome">genomes</a> vary widely among organisms, even those that are fairly closely <a title="Evolution" href="http://en.wikipedia.org/wiki/Evolution">evolutionarily</a> related. Although it was believed before the completion of the <a title="Human Genome Project" href="http://en.wikipedia.org/wiki/Human_Genome_Project">Human Genome Project</a> that the <a title="Human genome" href="http://en.wikipedia.org/wiki/Human_genome">human genome</a> would contain many more genes than simpler animals such as <a title="Mouse" href="http://en.wikipedia.org/wiki/Mouse">mice</a> or <a title="Drosophila" href="http://en.wikipedia.org/wiki/Drosophila">fruit flies</a>, the completion of the project has revealed that the human genome has an unexpectedly low gene density.<sup class="reference" id="_ref-IHSGC2004_2"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-IHSGC2004">[6]</a></sup> Estimates of the number of genes in a genome are difficult to compile because they depend on <a class="mw-redirect" title="Gene finding" href="http://en.wikipedia.org/wiki/Gene_finding">gene finding</a> <a title="Algorithm" href="http://en.wikipedia.org/wiki/Algorithm">algorithms</a> that search for patterns resembling those present in known genes, such as <a title="Open reading frame" href="http://en.wikipedia.org/wiki/Open_reading_frame">open reading frames</a>, <a title="Promoter" href="http://en.wikipedia.org/wiki/Promoter">promoter</a> regions with sequences resembling the <a title="Consensus sequence" href="http://en.wikipedia.org/wiki/Consensus_sequence">consensus</a> promoter sequence, and related regulatory regions such as <a title="TATA box" href="http://en.wikipedia.org/wiki/TATA_box">TATA boxes</a> in eukaryotes. Gene finding is less reliable in eukaryotic than in prokaryotic genomes due to the presence of non-coding DNA such as <a title="Intron" href="http://en.wikipedia.org/wiki/Intron">introns</a> and <a title="Pseudogene" href="http://en.wikipedia.org/wiki/Pseudogene">pseudogenes</a>.<sup class="reference" id="_ref-Mount_2004_0"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-Mount_2004">[17]</a></sup> Computational gene finding methods are still significantly more reliable than earlier techniques that required mapping the locations of specific mutations that gave rise to distinguishable alleles.<sup class="reference" id="_ref-Watson_2004_4"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-Watson_2004">[8]</a></sup></p>
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| − | <p>In most <a title="Eukaryote" href="http://en.wikipedia.org/wiki/Eukaryote">eukaryotic</a> species, very little of the DNA in the genome encodes proteins, and the genes may be separated by vast regions of <a class="mw-redirect" title="Non-coding DNA" href="http://en.wikipedia.org/wiki/Non-coding_DNA">non-coding DNA</a>, much of which has been labeled "<a title="Junk DNA" href="http://en.wikipedia.org/wiki/Junk_DNA">junk DNA</a>" due to its apparent lack of function in the modern organism. A commonly studied type of "junk DNA" is the <a title="Pseudogene" href="http://en.wikipedia.org/wiki/Pseudogene">pseudogenes</a>, or region of non-coding DNA that resembles expressed genes but usually lacks appropriate promoters and other control sequences; such regions are hypothesized to be the results of <a title="Gene duplication" href="http://en.wikipedia.org/wiki/Gene_duplication">gene duplication</a> events in a lineage's <a title="Evolution" href="http://en.wikipedia.org/wiki/Evolution">evolutionary</a> past.<sup class="reference" id="_ref-Lodish_0"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-Lodish">[18]</a></sup> Moreover, the genes are often fragmented internally by non-coding sequences called <a title="Intron" href="http://en.wikipedia.org/wiki/Intron">introns</a>, which can be many times longer than the coding sequence but are <a title="Splicing (genetics)" href="http://en.wikipedia.org/wiki/Splicing_%28genetics%29">spliced</a> during <a title="Post-transcriptional modification" href="http://en.wikipedia.org/wiki/Post-transcriptional_modification">post-transcriptional modification</a> of pre-<a class="mw-redirect" title="MRNA" href="http://en.wikipedia.org/wiki/MRNA">mRNA</a>.</p>
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| − | <p><a id="Genetic_and_genomic_nomenclature" name="Genetic_and_genomic_nomenclature"></a></p>
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| − | <h3><span class="editsection">[<a title="Edit section: Genetic and genomic nomenclature" href="http://en.wikipedia.org/w/index.php?title=Gene&action=edit&section=17">edit</a>]</span> <span class="mw-headline">Genetic and genomic nomenclature</span></h3>
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| − | <p><a title="Gene nomenclature" href="http://en.wikipedia.org/wiki/Gene_nomenclature">Gene nomenclature</a> has been established by the <a class="mw-redirect" title="HUGO" href="http://en.wikipedia.org/wiki/HUGO">HUGO</a> Gene Nomenclature Committee (HGNC) for each known human gene in the form of an approved gene name and <a title="Symbol" href="http://en.wikipedia.org/wiki/Symbol">symbol</a> (short-form <a title="Abbreviation" href="http://en.wikipedia.org/wiki/Abbreviation">abbreviation</a>). All approved symbols are stored in the <a class="external text" title="http://www.genenames.org/cgi-bin/hgnc_search.pl" rel="nofollow" href="http://www.genenames.org/cgi-bin/hgnc_search.pl">HGNC Database</a>. Each symbol is unique and each gene is only given one approved gene symbol. It is necessary to provide a unique symbol for each gene so that people can talk about them. This also facilitates <a title="Electronics" href="http://en.wikipedia.org/wiki/Electronics">electronic</a> <a title="Data" href="http://en.wikipedia.org/wiki/Data">data</a> retrieval from publications. In preference each symbol maintains parallel construction in different members of a <a title="Gene family" href="http://en.wikipedia.org/wiki/Gene_family">gene family</a> and can be used in other <a title="Species" href="http://en.wikipedia.org/wiki/Species"><font color="#810081">species</font></a>, especially the <a title="Mouse" href="http://en.wikipedia.org/wiki/Mouse">mouse</a>.</p>
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| − | <p><a id="Evolutionary_concept_of_a_gene" name="Evolutionary_concept_of_a_gene"></a></p>
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| − | <h2><span class="editsection">[<a title="Edit section: Evolutionary concept of a gene" href="http://en.wikipedia.org/w/index.php?title=Gene&action=edit&section=18">edit</a>]</span> <span class="mw-headline">Evolutionary concept of a gene</span></h2>
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| − | <p><a title="George C. Williams" href="http://en.wikipedia.org/wiki/George_C._Williams">George C. Williams</a> first explicitly advocated the <a title="Gene-centered view of evolution" href="http://en.wikipedia.org/wiki/Gene-centered_view_of_evolution">gene-centric view of evolution</a> in his 1966 book <em><a title="Adaptation and Natural Selection" href="http://en.wikipedia.org/wiki/Adaptation_and_Natural_Selection">Adaptation and Natural Selection</a></em>. He proposed an evolutionary concept of gene to be used when we are talking about <a title="Natural selection" href="http://en.wikipedia.org/wiki/Natural_selection">natural selection</a> favoring some genes. The definition is: "that which segregates and recombines with appreciable frequency." According to this definition, even an <a title="Asexuality" href="http://en.wikipedia.org/wiki/Asexuality">asexual</a> genome could be considered a gene, insofar it have an appreciable permanency through many generations.</p>
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| − | <p>The difference is: the molecular gene <em>transcribes</em> as a unit, and the evolutionary gene <em>inherits</em> as a unit.</p>
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| − | <p><a title="Richard Dawkins" href="http://en.wikipedia.org/wiki/Richard_Dawkins">Richard Dawkins</a>' <em><a title="The Selfish Gene" href="http://en.wikipedia.org/wiki/The_Selfish_Gene">The Selfish Gene</a></em> and <em><a title="The Extended Phenotype" href="http://en.wikipedia.org/wiki/The_Extended_Phenotype">The Extended Phenotype</a></em> defended the idea that the gene is the only <a title="DNA replication" href="http://en.wikipedia.org/wiki/DNA_replication">replicator</a> in living systems. This means that only genes transmit their structure largely intact and are potentially immortal in the form of copies. So, genes should be the <a title="Unit of selection" href="http://en.wikipedia.org/wiki/Unit_of_selection">unit of selection</a>. In <em><a title="The Selfish Gene" href="http://en.wikipedia.org/wiki/The_Selfish_Gene">The Selfish Gene</a></em> Dawkins attempts to redefine the word 'gene' to mean "an inheritable unit" instead of the generally accepted definition of "a section of DNA coding for a particular protein". In <em><a class="mw-redirect" title="River Out of Eden" href="http://en.wikipedia.org/wiki/River_Out_of_Eden">River Out of Eden</a></em>, Dawkins further refined the idea of gene-centric selection by describing life as a river of compatible genes flowing through <a class="mw-redirect" title="Geological time" href="http://en.wikipedia.org/wiki/Geological_time">geological time</a>. Scoop up a bucket of genes from the river of genes, and we have an <a title="Organism" href="http://en.wikipedia.org/wiki/Organism">organism</a> serving as temporary bodies or <a class="mw-redirect" title="Survival machine" href="http://en.wikipedia.org/wiki/Survival_machine">survival machines</a>. A river of genes may fork into two branches representing two non-<a title="Hybrid" href="http://en.wikipedia.org/wiki/Hybrid">interbreeding</a> <a title="Species" href="http://en.wikipedia.org/wiki/Species"><font color="#810081">species</font></a> as a result of geographical separation.</p>
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| − | <p><a id="Gene_targeting_and_implications" name="Gene_targeting_and_implications"></a></p>
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| − | <h2><span class="mw-headline">Gene targeting and implications</span></h2>
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| − | <p>Gene targeting is commonly referred to techniques for altering or disrupting mouse genes and provides the mouse models for studying the roles of individual genes in <a class="mw-redirect" title="Embryonic development" href="http://en.wikipedia.org/wiki/Embryonic_development">embryonic development</a>, human disorders, aging and diseases. The mouse models, where one or more of its genes are deactivated or made inoperable, are called <a class="mw-redirect" title="Knockout mice" href="http://en.wikipedia.org/wiki/Knockout_mice">knockout mice</a>. Since the first reports in which <a title="Homologous recombination" href="http://en.wikipedia.org/wiki/Homologous_recombination">homologous recombination</a> in <a title="Embryonic stem cell" href="http://en.wikipedia.org/wiki/Embryonic_stem_cell">embryonic stem cells</a> was used to generate gene-targeted mice,<sup class="reference" id="_ref-2"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-2">[19]</a></sup> gene targeting has proven to be a powerful means of precisely manipulating the mammalian genome, producing at least ten thousand mutant mouse strains and it is now possible to introduce mutations that can be activated at specific time points, or in specific cells or organs, both during development and in the adult animal.<sup class="reference" id="_ref-3"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-3">[20]</a></sup><sup class="reference" id="_ref-Deng_2007_0"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-Deng_2007">[21]</a></sup></p>
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| − | <p>Gene targeting strategies have been expanded to all kinds of modifications, including <a title="Point mutation" href="http://en.wikipedia.org/wiki/Point_mutation">point mutations</a>, isoform deletions, mutant allele correction, large pieces of chromosomal DNA <a title="Genetic insertion" href="http://en.wikipedia.org/wiki/Genetic_insertion">insertion</a> and <a title="Deletion (genetics)" href="http://en.wikipedia.org/wiki/Deletion_%28genetics%29">deletion</a>, tissue specific disruption combined with spatial and temporal regulation and so on. It is predicted that the ability to generate mouse models with predictable phenotypes will have a major impact on studies of all phases of development, <a title="Immunology" href="http://en.wikipedia.org/wiki/Immunology">immunology</a>, <a title="Neurobiology" href="http://en.wikipedia.org/wiki/Neurobiology">neurobiology</a>, <a title="Oncology" href="http://en.wikipedia.org/wiki/Oncology">oncology</a>, <a title="Physiology" href="http://en.wikipedia.org/wiki/Physiology">physiology</a>, <a title="Metabolism" href="http://en.wikipedia.org/wiki/Metabolism">metabolism</a>, and human diseases. Gene targeting is also in theory applicable to species from which <a title="Totipotency" href="http://en.wikipedia.org/wiki/Totipotency">totipotent</a> embryonic stem cells can be established, and therefore may offer a potential to the improvement of domestic animals and plants.<sup class="reference" id="_ref-Deng_2007_1"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-Deng_2007">[21]</a></sup><sup class="reference" id="_ref-4"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-4">[22]</a></sup></p>
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| − | <p><a id="The_gene_concept_is_still_changing" name="The_gene_concept_is_still_changing"></a></p>
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| − | <h2><span class="mw-headline">The <em>gene</em> concept is still changing</span></h2>
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| − | <p>The concept of the gene has changed considerably (see <a title="Gene" href="http://en.wikipedia.org/wiki/Gene#history">history section</a>). Originally considered a "unit of inheritance" to a usually <a title="DNA" href="http://en.wikipedia.org/wiki/DNA">DNA</a>-based unit that can exert its effects on the organism through <a title="RNA" href="http://en.wikipedia.org/wiki/RNA">RNA</a> or <a title="Protein" href="http://en.wikipedia.org/wiki/Protein">protein</a> products. It was also previously believed that one gene makes one protein; this concept has been overthrown by the discovery of <a title="Alternative splicing" href="http://en.wikipedia.org/wiki/Alternative_splicing">alternative splicing</a> and <a title="Trans-splicing" href="http://en.wikipedia.org/wiki/Trans-splicing">trans-splicing</a>.<sup class="reference" id="_ref-Gerstein_2"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-Gerstein">[10]</a></sup></p>
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| − | <p>And the definition of gene is still changing. The first cases of <a title="RNA" href="http://en.wikipedia.org/wiki/RNA">RNA</a>-based <a title="Biological inheritance" href="http://en.wikipedia.org/wiki/Biological_inheritance">inheritance</a> have been discovered in mammals.<sup class="reference" id="_ref-rass_1"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-rass">[14]</a></sup> In plants, cases of traits reappearing after several generations of absence have led researchers to hypothesise RNA-directed overwriting of genomic DNA.<sup class="reference" id="_ref-5"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-5">[23]</a></sup> Evidence is also accumulating that the <a title="Enhancer (genetics)" href="http://en.wikipedia.org/wiki/Enhancer_%28genetics%29">control regions</a> of a gene do not necessarily have to be close to the <a class="mw-redirect" title="Coding sequence" href="http://en.wikipedia.org/wiki/Coding_sequence">coding sequence</a> on the linear molecule or even on the same chromosome. Spilianakis and colleagues discovered that the <a class="mw-redirect" title="Promoter region" href="http://en.wikipedia.org/wiki/Promoter_region">promoter region</a> of the <a title="Interferon-gamma" href="http://en.wikipedia.org/wiki/Interferon-gamma">interferon-gamma</a> gene on chromosome 10 and the regulatory regions of the T(H)2 <a title="Cytokine" href="http://en.wikipedia.org/wiki/Cytokine">cytokine</a> locus on chromosome 11 come into close proximity in the <a title="Cell nucleus" href="http://en.wikipedia.org/wiki/Cell_nucleus">nucleus</a> possibly to be jointly regulated.<sup class="reference" id="_ref-6"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-6">[24]</a></sup></p>
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| − | <p>The concept that genes are clearly delimited is also being eroded. There is evidence for fused proteins stemming from two adjacent genes that can produce two separate protein products. While it is not clear whether these fusion proteins are functional, the phenomena is more frequent than previously thought.<sup class="reference" id="_ref-7"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-7">[25]</a></sup> Even more ground-breaking than the discovery of fused genes is the observation that some proteins can be composed of <a class="mw-redirect" title="Exons" href="http://en.wikipedia.org/wiki/Exons">exons</a> from far away regions and even different chromosomes.<sup class="reference" id="_ref-8"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-8">[26]</a></sup><sup class="reference" id="_ref-Rethink_2"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-Rethink">[2]</a></sup> This new data has led to an updated, and probably tentative, definition of a gene as "a union of genomic sequences encoding a coherent set of potentially overlapping functional products."<sup class="reference" id="_ref-Gerstein_3"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-Gerstein">[10]</a></sup> This new definition categorizes genes by functional products, whether they be proteins or RNA, rather than specific DNA loci; all regulatory elements of DNA are therefore classified as <em>gene-associated</em> regions.<sup class="reference" id="_ref-Gerstein_4"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-Gerstein">[10]</a></sup></p>
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| − | <p><a id="See_also" name="See_also"></a></p>
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| − | <h2><span class="mw-headline">See also</span></h2>
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| − | <div style="-moz-column-count: 3; column-count: 3">
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| − | <ul>
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| − | <li><a title="DNA" href="http://en.wikipedia.org/wiki/DNA">DNA</a> </li>
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| − | <li><a title="Epigenetics" href="http://en.wikipedia.org/wiki/Epigenetics">Epigenetics</a> </li>
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| − | <li><a title="Gene-centered view of evolution" href="http://en.wikipedia.org/wiki/Gene-centered_view_of_evolution">Gene-centric view of evolution</a> </li>
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| − | <li><a title="Gene expression" href="http://en.wikipedia.org/wiki/Gene_expression">Gene expression</a> </li>
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| − | <li><a title="Gene family" href="http://en.wikipedia.org/wiki/Gene_family">Gene family</a> </li>
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| − | <li><a title="Gene pool" href="http://en.wikipedia.org/wiki/Gene_pool">Gene pool</a> </li>
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| − | <li><a title="Gene therapy" href="http://en.wikipedia.org/wiki/Gene_therapy">Gene therapy</a> </li>
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| − | <li><a title="Genetic algorithm" href="http://en.wikipedia.org/wiki/Genetic_algorithm">Genetic algorithm</a> </li>
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| − | <li><a title="Genetic programming" href="http://en.wikipedia.org/wiki/Genetic_programming">Genetic programming</a> </li>
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| − | <li><a title="Gene regulatory network" href="http://en.wikipedia.org/wiki/Gene_regulatory_network">Gene regulatory network</a> </li>
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| − | <li><a title="Genetics" href="http://en.wikipedia.org/wiki/Genetics">Genetics</a> </li>
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| − | <li><a title="Genome" href="http://en.wikipedia.org/wiki/Genome">Genome</a> </li>
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| − | <li><a title="Genomics" href="http://en.wikipedia.org/wiki/Genomics">Genomics</a> </li>
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| − | <li><a title="Homeobox" href="http://en.wikipedia.org/wiki/Homeobox">Homeobox</a> </li>
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| − | <li><a title="Human Genome Project" href="http://en.wikipedia.org/wiki/Human_Genome_Project">Human Genome Project</a> </li>
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| − | <li><a class="mw-redirect" title="List of notable genes" href="http://en.wikipedia.org/wiki/List_of_notable_genes">List of notable genes</a> </li>
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| − | <li><a title="Meme" href="http://en.wikipedia.org/wiki/Meme">Meme</a> </li>
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| − | <li><a title="Pseudogene" href="http://en.wikipedia.org/wiki/Pseudogene">Pseudogene</a> </li>
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| − | <li><a title="Regulation of gene expression" href="http://en.wikipedia.org/wiki/Regulation_of_gene_expression">Regulation of gene expression</a> </li>
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| − | <li><a title="Smart gene" href="http://en.wikipedia.org/wiki/Smart_gene">Smart gene</a> </li>
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| − | </ul>
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| − | </div>
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| − | <p><span class="mw-headline"><font size="5">References</font></span></p>
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| − | <div class="references-small" style="-moz-column-count: 2; column-count: 2; -webkit-column-count: 2">
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| − | <ol class="references">
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| − | <li id="_note-Pearson_2006">^ <a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-Pearson_2006_0"><sup><em><strong>a</strong></em></sup></a> <a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-Pearson_2006_1"><sup><em><strong>b</strong></em></sup></a> <cite style="FONT-STYLE: normal">Pearson H (2006). "Genetics: what is a gene?". <em>Nature</em> 441 (7092): 398-401. <a class="external" title="http://www.ncbi.nlm.nih.gov/pubmed/16724031" href="http://www.ncbi.nlm.nih.gov/pubmed/16724031">PMID 16724031</a>.</cite><span class="Z3988" title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.atitle=Genetics%3A+what+is+a+gene%3F&rft.jtitle=Nature&rft.date=2006&rft.volume=441&rft.issue=7092&rft.au=Pearson+H&rft.pages=398-401&rft_id=info:pmid/16724031"> </span> </li>
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| − | <li id="_note-Rethink">^ <a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-Rethink_0"><sup><em><strong>a</strong></em></sup></a> <a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-Rethink_1"><sup><em><strong>b</strong></em></sup></a> <a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-Rethink_2"><sup><em><strong>c</strong></em></sup></a> <cite style="FONT-STYLE: normal">Elizabeth Pennisi (2007). "DNA Study Forces Rethink of What It Means to Be a Gene". <em>Science</em> 316 (5831): 1556-1557.</cite><span class="Z3988" title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.atitle=DNA+Study+Forces+Rethink+of+What+It+Means+to+Be+a+Gene&rft.jtitle=Science&rft.date=2007&rft.volume=316&rft.issue=5831&rft.au=Elizabeth+Pennisi&rft.pages=1556-1557"> </span> </li>
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| − | <li id="_note-0"><strong><a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-0">^</a></strong> see eg <a title="Martin Nowak" href="http://en.wikipedia.org/wiki/Martin_Nowak">Martin Nowak</a>'s <em>Evolutionary Dynamics</em> </li>
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| − | <li id="_note-Gerstein_2007"><strong><a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-Gerstein_2007_0">^</a></strong> <cite style="FONT-STYLE: normal">Gerstein MB, Bruce C, Rozowsky JS, Zheng D, Du J, Korbel JO, Emanuelsson O, Zhang ZD, Weissman S, Snyder M (2007). "What is a gene, post-ENCODE? History and updated definition". <em>Genome Research</em> 17 (6): 669-681. <a class="external" title="http://www.ncbi.nlm.nih.gov/pubmed/17567988" href="http://www.ncbi.nlm.nih.gov/pubmed/17567988">PMID 17567988</a>.</cite><span class="Z3988" title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.atitle=What+is+a+gene%2C+post-ENCODE%3F+History+and+updated+definition&rft.jtitle=Genome+Research&rft.date=2007&rft.volume=17&rft.issue=6&rft.au=Gerstein+MB%2C+Bruce+C%2C+Rozowsky+JS%2C+Zheng+D%2C+Du+J%2C+Korbel+JO%2C+Emanuelsson+O%2C+Zhang+ZD%2C+Weissman+S%2C+Snyder+M&rft.pages=669-681&rft_id=info:pmid/17567988"> </span> </li>
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| − | <li id="_note-Cavalier-Smith"><strong><a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-Cavalier-Smith_0">^</a></strong> Cavalier-Smith T. (1985). Eukaryotic gene numbers, non-coding DNA, and genome size. In Cavalier-Smith T, ed. <em>The Evolution of Genome Size</em> Chichester: John Wiley. </li>
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| − | <li id="_note-IHSGC2004">^ <a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-IHSGC2004_0"><sup><em><strong>a</strong></em></sup></a> <a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-IHSGC2004_1"><sup><em><strong>b</strong></em></sup></a> <a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-IHSGC2004_2"><sup><em><strong>c</strong></em></sup></a> <cite style="FONT-STYLE: normal">International Human Genome Sequencing Consortium (2004). "<a class="external text" title="http://www.nature.com/nature/journal/v431/n7011/full/nature03001.html" rel="nofollow" href="http://www.nature.com/nature/journal/v431/n7011/full/nature03001.html">Finishing the euchromatic sequence of the human genome.</a>". <em>Nature</em> 431 (7011): 931-45. <a class="external" title="http://www.ncbi.nlm.nih.gov/pubmed/15496913" href="http://www.ncbi.nlm.nih.gov/pubmed/15496913">PMID 15496913</a>.</cite><span class="Z3988" title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.atitle=Finishing+the+euchromatic+sequence+of+the+human+genome.&rft.jtitle=Nature&rft.date=2004&rft.volume=431&rft.issue=7011&rft.au=International+Human+Genome+Sequencing+Consortium&rft.pages=931-45&rft_id=http%3A%2F%2Fwww.nature.com%2Fnature%2Fjournal%2Fv431%2Fn7011%2Ffull%2Fnature03001.html"> </span> </li>
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| − | <li id="_note-gene_count2007">^ <a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-gene_count2007_0"><sup><em><strong>a</strong></em></sup></a> <a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-gene_count2007_1"><sup><em><strong>b</strong></em></sup></a> <cite style="FONT-STYLE: normal">Pennisi, Elizabeth (2007). "<a class="external text" title="http://www.sciencemag.org/cgi/content/full/316/5828/1113a?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=gene+count&searchid=1&FIRSTINDEX=0&resourcetype=HWCIT" rel="nofollow" href="http://www.sciencemag.org/cgi/content/full/316/5828/1113a?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=gene+count&searchid=1&FIRSTINDEX=0&resourcetype=HWCIT">Working the (Gene Count) Numbers_ Finally, a Firm Answer</a>". <em>Science</em> 316 (5828): 1113.</cite><span class="Z3988" title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.atitle=Working+the+%28Gene+Count%29+Numbers_+Finally%2C+a+Firm+Answer&rft.jtitle=Science&rft.date=2007&rft.volume=316&rft.issue=5828&rft.au=Pennisi%2C+Elizabeth&rft.pages=1113&rft_id=http%3A%2F%2Fwww.sciencemag.org%2Fcgi%2Fcontent%2Ffull%2F316%2F5828%2F1113a%3Fmaxtoshow%3D%26HITS%3D10%26hits%3D10%26RESULTFORMAT%3D%26fulltext%3Dgene%2Bcount%26searchid%3D1%26FIRSTINDEX%3D0%26resourcetype%3DHWCIT"> </span> </li>
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| − | <li id="_note-Watson_2004">^ <a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-Watson_2004_0"><sup><em><strong>a</strong></em></sup></a> <a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-Watson_2004_1"><sup><em><strong>b</strong></em></sup></a> <a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-Watson_2004_2"><sup><em><strong>c</strong></em></sup></a> <a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-Watson_2004_3"><sup><em><strong>d</strong></em></sup></a> <a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-Watson_2004_4"><sup><em><strong>e</strong></em></sup></a> <cite class="book" style="FONT-STYLE: normal">Watson JD, Baker TA, Bell SP, Gann A, Levine M, Losick R (2004). <em>Molecular Biology of the Gene</em>, 5th ed., Peason Benjamin Cummings (Cold Spring Harbor Laboratory Press). <a class="internal" href="http://en.wikipedia.org/w/index.php?title=Special:Booksources&isbn=080534635X">ISBN 080534635X</a>.</cite><span class="Z3988" title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Molecular+Biology+of+the+Gene&rft.au=Watson+JD%2C+Baker+TA%2C+Bell+SP%2C+Gann+A%2C+Levine+M%2C+Losick+R&rft.edition=5th+ed.&rft.pub=Peason+Benjamin+Cummings+%28Cold+Spring+Harbor+Laboratory+Press%29"> </span> </li>
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| − | <li id="_note-pangen">^ <a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-pangen_0"><sup><em><strong>a</strong></em></sup></a> <a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-pangen_1"><sup><em><strong>b</strong></em></sup></a> Vries, H. de (1889) <em>Intracellular Pangenesis</em> <a class="external autonumber" title="http://www.esp.org/books/devries/pangenesis/facsimile/" rel="nofollow" href="http://www.esp.org/books/devries/pangenesis/facsimile/">[1]</a> ("pangen" definition on page 7 and 40 of this 1910 translation in English) </li>
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| − | <li id="_note-Gerstein">^ <a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-Gerstein_0"><sup><em><strong>a</strong></em></sup></a> <a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-Gerstein_1"><sup><em><strong>b</strong></em></sup></a> <a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-Gerstein_2"><sup><em><strong>c</strong></em></sup></a> <a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-Gerstein_3"><sup><em><strong>d</strong></em></sup></a> <a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-Gerstein_4"><sup><em><strong>e</strong></em></sup></a> Mark B. Gerstein <em>et al.</em>, "What is a gene, post-ENCODE? History and updated definition," <em>Genome Research</em> 17(6) (2007): 669-681 </li>
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| − | <li id="_note-Min_1972"><strong><a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-Min_1972_0">^</a></strong> <cite style="FONT-STYLE: normal">Min Jou W, Haegeman G, Ysebaert M, Fiers W (1972). "Nucleotide sequence of the gene coding for the bacteriophage MS2 coat protein". <em>Nature</em> 237 (5350): 82-8. <a class="external" title="http://www.ncbi.nlm.nih.gov/pubmed/4555447" href="http://www.ncbi.nlm.nih.gov/pubmed/4555447">PMID 4555447</a>.</cite><span class="Z3988" title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.atitle=Nucleotide+sequence+of+the+gene+coding+for+the+bacteriophage+MS2+coat+protein&rft.jtitle=Nature&rft.date=1972&rft.volume=237&rft.issue=5350&rft.au=Min+Jou+W%2C+Haegeman+G%2C+Ysebaert+M%2C+Fiers+W&rft.pages=82-8&rft_id=info:pmid/4555447"> </span> </li>
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| − | <li id="_note-genome"><strong><a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-genome_0">^</a></strong> <a class="external text" title="http://www.genome.gov/Pages/Education/Kit/main.cfm?pageid=24" rel="nofollow" href="http://www.genome.gov/Pages/Education/Kit/main.cfm?pageid=24">The Human Genome Project Timeline</a>. Retrieved on <a title="2006" href="http://en.wikipedia.org/wiki/2006">2006</a>-<a title="September 13" href="http://en.wikipedia.org/wiki/September_13">09-13</a>. </li>
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| − | <li id="_note-Darwin"><strong><a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-Darwin_0">^</a></strong> Darwin C. (1868). Animals and Plants under Domestication (1868). </li>
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| − | <li id="_note-rass">^ <a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-rass_0"><sup><em><strong>a</strong></em></sup></a> <a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-rass_1"><sup><em><strong>b</strong></em></sup></a> <cite style="FONT-STYLE: normal">Rassoulzadegan M, Grandjean V, Gounon P, Vincent S, Gillot I, Cuzin F (2006). "RNA-mediated non-mendelian inheritance of an epigenetic change in the mouse". <em>Nature</em> 441 (7092): 469-74. <a class="external" title="http://www.ncbi.nlm.nih.gov/pubmed/16724059" href="http://www.ncbi.nlm.nih.gov/pubmed/16724059">PMID 16724059</a>.</cite><span class="Z3988" title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.atitle=RNA-mediated+non-mendelian+inheritance+of+an+epigenetic+change+in+the+mouse&rft.jtitle=Nature&rft.date=2006&rft.volume=441&rft.issue=7092&rft.au=Rassoulzadegan+M%2C+Grandjean+V%2C+Gounon+P%2C+Vincent+S%2C+Gillot+I%2C+Cuzin+F&rft.pages=469-74&rft_id=info:pmid/16724059"> </span> </li>
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| − | <li id="_note-1"><strong><a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-1">^</a></strong> <cite style="FONT-STYLE: normal">Woodson SA (1998). "<a class="external text" title="http://www.genesdev.org/cgi/content/full/12/9/1243" rel="nofollow" href="http://www.genesdev.org/cgi/content/full/12/9/1243">Ironing out the kinks: splicing and translation in bacteria</a>". <em>Genes Dev.</em> 12 (9): 1243–7. <a class="external" title="http://www.ncbi.nlm.nih.gov/pubmed/9573040" href="http://www.ncbi.nlm.nih.gov/pubmed/9573040">PMID 9573040</a>.</cite><span class="Z3988" title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.atitle=Ironing+out+the+kinks%3A+splicing+and+translation+in+bacteria&rft.jtitle=Genes+Dev.&rft.date=1998&rft.volume=12&rft.issue=9&rft.au=Woodson+SA&rft.pages=1243%E2%80%937&rft_id=info:pmid/9573040&rft_id=http%3A%2F%2Fwww.genesdev.org%2Fcgi%2Fcontent%2Ffull%2F12%2F9%2F1243"> </span> </li>
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| − | <li id="_note-Braig"><strong><a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-Braig_0">^</a></strong> <cite style="FONT-STYLE: normal">Braig M, Schmitt C (2006). "Oncogene-induced senescence: putting the brakes on tumor development". <em>Cancer Res</em> 66 (6): 2881-4. <a class="external" title="http://www.ncbi.nlm.nih.gov/pubmed/16540631" href="http://www.ncbi.nlm.nih.gov/pubmed/16540631">PMID 16540631</a>.</cite><span class="Z3988" title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.atitle=Oncogene-induced+senescence%3A+putting+the+brakes+on+tumor+development&rft.jtitle=Cancer+Res&rft.date=2006&rft.volume=66&rft.issue=6&rft.au=Braig+M%2C+Schmitt+C&rft.pages=2881-4&rft_id=info:pmid/16540631"> </span> </li>
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| − | <li id="_note-Mount_2004"><strong><a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-Mount_2004_0">^</a></strong> <cite class="book" id="Reference-Mount-2004" style="FONT-STYLE: normal">Mount, DW (2004). <em>Bioinformatics: Sequence and genome analysis</em>, 2nd ed., Cold Spring Harbor Laboratory Press: Cold Spring Harbor, New York. <a class="internal" href="http://en.wikipedia.org/w/index.php?title=Special:Booksources&isbn=0879697121">ISBN 0879697121</a>.</cite><span class="Z3988" title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Bioinformatics%3A+Sequence+and+genome+analysis&rft.aulast=Mount&rft.aufirst=DW&rft.edition=2nd+ed.&rft.pub=Cold+Spring+Harbor+Laboratory+Press%3A+Cold+Spring+Harbor%2C+New+York"> </span> </li>
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| − | <li id="_note-Lodish"><strong><a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-Lodish_0">^</a></strong> Lodish, H, Berk A, Matsudaira P, Kaiser CA, Krieger M, Scott MP, Zipursky SL, Darnell J. (2004). <em>Molecular Cell Biology</em>, 5th, New York: WH Freeman. </li>
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| − | <li id="_note-2"><strong><a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-2">^</a></strong> Thomas KR, Capecchi MR. Site-directed mutagenesis by gene targeting in mouse embryo-derived stem cells. Cell. 1987;51:503-12 </li>
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| − | <li id="_note-3"><strong><a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-3">^</a></strong> <a class="external free" title="http://nobelprize.org/nobel_prizes/medicine/laureates/2007/press.html" rel="nofollow" href="http://nobelprize.org/nobel_prizes/medicine/laureates/2007/press.html">http://nobelprize.org/nobel_prizes/medicine/laureates/2007/press.html</a> </li>
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| − | <li id="_note-Deng_2007">^ <a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-Deng_2007_0"><sup><em><strong>a</strong></em></sup></a> <a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-Deng_2007_1"><sup><em><strong>b</strong></em></sup></a> Deng C. In Celebration of Dr. Mario R. Capecchi's Nobel Prize. Int J Biol Sci 2007; 3:417-419. <a class="external free" title="http://www.biolsci.org/v03p0417.htm" rel="nofollow" href="http://www.biolsci.org/v03p0417.htm">http://www.biolsci.org/v03p0417.htm</a> </li>
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| − | <li id="_note-4"><strong><a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-4">^</a></strong> <a class="external free" title="http://www.hhmi.org/research/investigators/capecchi.html" rel="nofollow" href="http://www.hhmi.org/research/investigators/capecchi.html">http://www.hhmi.org/research/investigators/capecchi.html</a> </li>
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| − | <li id="_note-5"><strong><a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-5">^</a></strong> Lolle & colleagues (2005) Genome-wide non-mendelian inheritance of extra-genomic information in Arabidopsis. <a class="external" title="http://www.ncbi.nlm.nih.gov/pubmed/15785770" href="http://www.ncbi.nlm.nih.gov/pubmed/15785770">PMID 15785770</a> </li>
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| − | <li id="_note-6"><strong><a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-6">^</a></strong> Spilianakis & colleagues (2005) Interchromosomal associations between alternatively expressed loci. <a class="external" title="http://www.ncbi.nlm.nih.gov/pubmed/15880101" href="http://www.ncbi.nlm.nih.gov/pubmed/15880101">PMID 15880101</a> </li>
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| − | <li id="_note-7"><strong><a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-7">^</a></strong> Parra & colleagues (2006) Tandem chimerism as a means to increase protein complexity in the human genome. <a class="external" title="http://www.ncbi.nlm.nih.gov/pubmed/16344564" href="http://www.ncbi.nlm.nih.gov/pubmed/16344564">PMID 16344564</a> </li>
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| − | <li id="_note-8"><strong><a title="" href="http://en.wikipedia.org/wiki/Gene#_ref-8">^</a></strong> Kapranov & colleagues (2005) Examples of the complex architecture of the human transcriptome revealed by <a title="Rapid Amplification of cDNA Ends" href="http://en.wikipedia.org/wiki/Rapid_Amplification_of_cDNA_Ends">RACE</a> and high-density tiling arrays. <a class="external" title="http://www.ncbi.nlm.nih.gov/pubmed/15998911" href="http://www.ncbi.nlm.nih.gov/pubmed/15998911">PMID 15998911</a> </li>
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| − | </ol>
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| − | </div>
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| − | <p><a id="Further_reading" name="Further_reading"></a></p>
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| − | <h2><span class="mw-headline">Further reading</span></h2>
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| − | <ul>
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| − | <li><cite class="book" id="Reference-Dawkins-1990" style="FONT-STYLE: normal"><a title="Richard Dawkins" href="http://en.wikipedia.org/wiki/Richard_Dawkins">Dawkins, Richard</a> (1990). <em><a title="The Selfish Gene" href="http://en.wikipedia.org/wiki/The_Selfish_Gene">The Selfish Gene</a></em>. Oxford University Press. <a class="internal" href="http://en.wikipedia.org/w/index.php?title=Special:Booksources&isbn=0192860925">ISBN 0-19-286092-5</a>.</cite><span class="Z3988" title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=%5B%5BThe+Selfish+Gene%5D%5D&rft.aulast=Dawkins&rft.aufirst=Richard&rft.pub=Oxford+University+Press"> </span> <a class="external text" title="http://print.google.com/print?id=WkHO9HI7koEC" rel="nofollow" href="http://print.google.com/print?id=WkHO9HI7koEC">Google Book Search</a>; first published 1976. </li>
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| − | <li><cite class="book" id="Reference-Dawkins-1995" style="FONT-STYLE: normal"><a title="Richard Dawkins" href="http://en.wikipedia.org/wiki/Richard_Dawkins">Dawkins, Richard</a> (1995). <em><a class="mw-redirect" title="River Out of Eden" href="http://en.wikipedia.org/wiki/River_Out_of_Eden">River Out of Eden</a></em>. Basic Books. <a class="internal" href="http://en.wikipedia.org/w/index.php?title=Special:Booksources&isbn=0465069908">ISBN 0-465-06990-8</a>.</cite><span class="Z3988" title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=%5B%5BRiver+Out+of+Eden%5D%5D&rft.aulast=Dawkins&rft.aufirst=Richard&rft.pub=Basic+Books"> </span> </li>
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| − | </ul>
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| − | <p><a id="External_links" name="External_links"></a></p>
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| − | <h2><span class="mw-headline">External links</span></h2>
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| − | <ul>
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| − | <li><a class="external text" title="http://www.dnalc.org/" rel="nofollow" href="http://www.dnalc.org/">The Dolan DNA Learning Center</a> </li>
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| − | <li><a class="external text" title="http://www.dnai.org/" rel="nofollow" href="http://www.dnai.org/">DNA Interactive</a> </li>
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| − | <li><a class="external text" title="http://www.dnaftb.org/" rel="nofollow" href="http://www.dnaftb.org/">DNA From The Beginning</a> </li>
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| − | </ul>
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| − | <div class="floatnone"><span><a class="image" title="Wikibooks" href="http://en.wikipedia.org/wiki/Image:Wikibooks-logo-en.svg"></a></span></div>
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| − | </div>
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| − | <div style="MARGIN-LEFT: 60px"><a title="Wikibooks" href="http://en.wikipedia.org/wiki/Wikibooks">Wikibooks</a> has a book on the topic of
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| − | <div style="MARGIN-LEFT: 10px"><em><strong><a class="extiw" title="wikibooks:Genes,_Technology_and_Policy" href="http://en.wikibooks.org/wiki/Genes%2C_Technology_and_Policy">Genes, Technology and Policy</a></strong></em></div>
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| − | <div class="infobox sisterproject noprint plainlinks" id="section_SpokenWikipedia">
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| − | <div style="TEXT-ALIGN: center"><strong>Listen to this article</strong> (<a title="Image:Gene.ogg" href="http://en.wikipedia.org/wiki/Image:Gene.ogg">info/dl</a>)<br />
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| − | <center>
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| − | <div id="ogg_player_1" style="WIDTH: 100px">
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| − | <p><br />
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| − | <div style="FLOAT: left; MARGIN-LEFT: 5px">
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| − | <div class="floatnone"><span><a class="image" title="Spoken Wikipedia" href="http://en.wikipedia.org/wiki/Image:Sound-icon.svg"></a></span></div>
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| − | </div>
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| − | <div style="FONT-SIZE: xx-small; MARGIN-LEFT: 60px; LINE-HEIGHT: 1.6em">This audio file was created from a revision dated <a title="2005" href="http://en.wikipedia.org/wiki/2005">2005</a>-<a title="April 21" href="http://en.wikipedia.org/wiki/April_21">04-21</a>, and may not reflect subsequent edits to the article. (<a title="Wikipedia:Media help" href="http://en.wikipedia.org/wiki/Wikipedia:Media_help">Audio help</a>)</div>
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| − | <div style="CLEAR: both; TEXT-ALIGN: center"><strong><a title="Wikipedia:Spoken articles" href="http://en.wikipedia.org/wiki/Wikipedia:Spoken_articles">More spoken articles</a></strong></div>
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| − | </div>
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| − | <div class="metadata topicon" id="spoken-icon" style="DISPLAY: none; RIGHT: 30px">
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| − | <div style="POSITION: relative"><a title="This is a spoken version of the article. Click here to listen." href="http://en.wikipedia.org/wiki/Media:Gene.ogg"></a></div>
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| − | <p> </p>
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| − | <h3><span class="mw-headline">Tutorial and news</span></h3>
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| − | <ul>
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| − | <li><a class="external text" title="http://www.scienceaid.co.uk/biology/genetics" rel="nofollow" href="http://www.scienceaid.co.uk/biology/genetics">Science aid: Genetics</a> for beginners </li>
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| − | <li><a class="external text" title="http://www.newscientist.com/news/news.jsp?id=ns99996561" rel="nofollow" href="http://www.newscientist.com/news/news.jsp?id=ns99996561">Recount slashes number of human genes</a> (from <a title="New Scientist" href="http://en.wikipedia.org/wiki/New_Scientist">New Scientist</a> magazine) </li>
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| − | <li><a class="external text" title="http://www.genome.gov/12513430" rel="nofollow" href="http://www.genome.gov/12513430">National Human Genome Research Institute — News Release</a> </li>
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| − | <li><cite style="FONT-STYLE: normal">(2004) "Finishing the euchromatic sequence of the human genome". <em>Nature</em> 431 (7011): 931-45. <a class="external" title="http://www.ncbi.nlm.nih.gov/pubmed/15496913" href="http://www.ncbi.nlm.nih.gov/pubmed/15496913">PMID 15496913</a>.</cite><span class="Z3988" title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.atitle=Finishing+the+euchromatic+sequence+of+the+human+genome&rft.jtitle=Nature&rft.date=2004&rft.volume=431&rft.issue=7011&rft.pages=931-45&rft_id=info:pmid/15496913"> </span> </li>
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| − | </ul>
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| − | <p><span class="mw-headline"><font size="5">References and databases</font></span></p>
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| − | <ul>
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| − | <li><a class="external text" title="http://www.gene.ucl.ac.uk/nomenclature" rel="nofollow" href="http://www.gene.ucl.ac.uk/nomenclature">HUGO Gene Nomenclature Committee, HGNC</a> </li>
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| − | <li><a class="external text" title="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=OMIM" rel="nofollow" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=OMIM">OMIM</a> NIH's National Library of Medicine NCBI website link to Online Mendelian Inheritance in Man. </li>
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| − | <li><a class="external text" title="http://www.hugo-international.org" rel="nofollow" href="http://www.hugo-international.org/">Human Genome Organisation, HUGO</a> </li>
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| − | <li><a class="external text" title="http://www.ihop-net.org/UniPub/iHOP/" rel="nofollow" href="http://www.ihop-net.org/UniPub/iHOP/">iHOP - Information Hyperlinked over Proteins</a> </li>
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| − | <li><a class="external text" title="http://www.pir.uniprot.org/" rel="nofollow" href="http://www.pir.uniprot.org/">UniProt</a> </li>
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| − | <li><a class="external text" title="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=gene" rel="nofollow" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=gene">Entrez Gene - A searchable database of genes</a> </li>
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| − | <li><a class="external text" title="http://idconverter.bioinfo.cnio.es" rel="nofollow" href="http://idconverter.bioinfo.cnio.es/">IDconverter - Map your ids to other known public DBs</a> </li>
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| − | <li><a class="external text" title="http://www.genecards.org" rel="nofollow" href="http://www.genecards.org/">GeneCards - the Human Gene Compendium</a> </li>
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| − | <li><a class="external text" title="http://www.genetherapynet.com" rel="nofollow" href="http://www.genetherapynet.com/">Gene Therapy Net</a> </li>
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| − | </ul>
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