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<p>A <strong>gene</strong> is a locatable region of <genomic sequence, corresponding to a class="mw-redirect" title="Genomic sequence" href="http:unit of inheritance, which is associated with regulatory regions, transcribed regions and//enor other functional sequence regions.wikipedia.org/wiki/Genomic_sequence<sup class=">genomic sequencereference" id="_ref-Pearson_2006_0">[1]</asup>, corresponding to a unit of <a titlesup class="Inheritancereference" hrefid="http://en.wikipedia.org/wiki/Inheritance_ref-Rethink_0">inheritance[2]</asup>, which is associated The physical development and phenotype of organisms can be thought of as a product of genes interacting with regulatory regions, transcribed regions each other and/or other functional sequence regions.with the environment<sup class="reference" id="_ref-Pearson_2006_00">[3]<a title="" href="http://en.wikipedia.org/wiki/Gene#_notesup> A concise definition of gene taking into account complex patterns of regulation and transcription, genic conservation and non-Pearson_2006">[1]</a></sup>coding RNA genes, has been proposed by Gerstein et al.<sup class="reference" id="_ref-Rethink_0Gerstein_2007_0">[4]<a title="" href="http://en.wikipedia.org/wiki/Gene#_note-Rethink"/sup>[2]"A gene is a union of genomic sequences encoding a coherent set of potentially overlapping functional products".</ap></supp>Colloquially, the term <strong> The physical <a title="Developmental biology" href="http://en.wikipedia.org/wiki/Developmental_biology">developmentgene</strong> is often used to refer to an inheritable trait which is usually accompanied by a> and <a title="Phenotype" href="http://enphenotype as in ("tall genes" or "bad genes") -- the proper scientific term for this is allele.wikipedia.org</wiki/Phenotype"p>phenotype</ap> In cells, genes consist of organisms can be thought a long strand of as DNA that contains a product promoter, which controls the activity of genes interacting with each other a gene, and coding and with non-coding sequence. Coding sequence determines what the environment<sup class="reference" id="_refgene produces, while non-0"><coding sequence can regulate the conditions of gene expression. When a title="" href="http://en.wikipedia.org/wiki/Gene#_notegene is active, the coding and non-0">[3]</coding sequence is copied in a></sup> A concise definition process called transcription, producing an RNA copy of the gene taking into account complex patterns 's information. This RNA can then direct the synthesis of regulation and transcriptionproteins via the genetic code. However, genic conservation and non-coding RNA genesRNAs can also be used directly, has been proposed by Gerstein et alfor example as part of the ribosome. These molecules resulting from gene expression, whether RNA or protein, are known as gene products.<sup class="reference" id="_ref-Gerstein_2007_0"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-Gerstein_2007"/p>[4]</a<p></sup> "A Genes often contain regions that do not encode products, but regulate gene is a union expression. The genes of genomic sequences encoding eukaryotic organisms can contain regions called introns that are removed from the messenger RNA in a coherent set of potentially overlapping functional process called splicing. The regions encoding gene products"are called exons.</p><p>ColloquiallyIn eukaryotes, the term a single gene can encode multiple proteins, which are produced through the creation of different arrangements of exons through <strongem>genealternative splicing</strongem> is . In prokaryotes (bacteria and archaea), introns are less common and genes often used to refer to an inheritable trait which is usually accompanied by contain a phenotype as in ("tall genes" or "bad genes") -- the proper scientific term single uninterrupted stretch of DNA, called a <em>cistron</em>, that codes for this is <a title="Allele" href="http://en.wikipedia.org/wiki/Allele">allele</a>.</p><p>In cells, genes consist product. Prokaryotic genes are often arranged in groups called operons with promoter and operator sequences that regulate transcription of a single long strand of <a title="DNA" href="http://enRNA.wikipediaThis RNA contains multiple coding sequences.org/wikiEach coding sequence is preceded by a Shine-Dalgarno sequence that ribosomes recognize.</DNA"p>DNA</ap> that contains a <a title="Promoter" href="http://enThe total set of genes in an organism is known as its genome.wikipedia.org/wiki/Promoter">promoter</a>An organism's genome size is generally lower in prokaryotes, which controls the activity both in number of a genebase pairs and number of genes, and coding and nonthan even single-coding sequencecelled eukaryotes. Coding sequence determines what the gene producesHowever, while non-coding sequence can regulate there is no clear relationship between genome sizes and complexity in eukaryotic organisms. One of the largest known genomes belongs to the conditions of single-celled amoeba <em>Amoeba dubia<a title="Gene expression" href="http://en.wikipediaem>, with over 670 billion base pairs, some 200 times larger than the human genome.org/wiki/Gene_expression<sup class=">gene expression<reference" id="_ref-Cavalier-Smith_0">[5]</asup>. When a gene is active, The estimated number of genes in the human genome has been repeatedly revised downward since the completion of the coding and non-coding sequence is copied in a process called <a title="Transcription (genetics)" href="http://en.wikipediaHuman Genome Project; current estimates place the human genome at just under 3 billion base pairs and about 20,000–25,000 genes.org/wiki/Transcription_%28genetics%29">transcription</sup class="reference" id="_ref-IHSGC2004_0"><a>, producing an RNA copy of the gene's information. This RNA can then direct the synthesis of proteins via the <a title="Genetic code" href=title="" href="http://en.wikipedia.org/wiki/Genetic_codeGene#_note-IHSGC2004">genetic code[6]</a>. However, RNAs can also be used directly, for example as part of the <a /sup> A recent <em><a title="RibosomeScience (journal)" href="http://en.wikipedia.org/wiki/RibosomeScience_%28journal%29">ribosomeScience</a>. These molecules resulting from gene expression, whether </em> article gives a titlefinal number of 20,488, with perhaps 100 more yet to be discovered .<sup class="RNAreference" hrefid="http://en.wikipedia.org/wiki/RNA_ref-gene_count2007_0">RNA</a> or <a title="Protein" href="http://en.wikipedia.org/wiki/ProteinGene#_note-gene_count2007">protein[7]</a>, are known as </sup> The gene density of a genome is a title="Gene product" href="http://en.wikipedia.org/wiki/Gene_product">gene products</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.</p><p>Genes often contain regions that do not encode products, but <a sup class="mwreference" id="_ref-redirectWatson_2004_0" ><a title="Gene regulation" href="http://en.wikipedia.org/wiki/Gene_regulationGene#_note-Watson_2004">regulate gene expression[8]</a>. The genes of <a title/sup></p><p><span class="Eukaryotemw-headline" href><font size="http://en.wikipedia.org/wiki/Eukaryote">eukaryotic</a> organisms can contain regions called <a title="Intron" href="http://en.wikipedia.org/wiki/Intron">introns</a> that are removed from the messenger RNA in a process called <a title="Splicing (genetics)" href="http://en.wikipedia.org/wiki/Splicing_%28genetics%29">splicing</a>. The regions encoding gene products are called <a title="Exon" href="http://en.wikipedia.org/wiki/Exon">exons</a>. 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 <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>), 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 <a class="mw-redirect" title="Operons" href="http://en.wikipedia.org/wiki/Operons">operons</a> with <a title="Promoter" href="http://en.wikipedia.org/wiki/Promoter">promoter</a> and <a title="Operator" href="http://en.wikipedia.org/wiki/Operator">operator</a> sequences that regulate <a title="Transcription (genetics)" href="http://en.wikipedia.org/wiki/Transcription_%28genetics%29">transcription</a> of a single long <a title="RNA" href="http://en.wikipedia.org/wiki/RNA">RNA</a>. This RNA contains multiple coding sequences. Each coding sequence is preceded by a <a title="Shine-Dalgarno sequence" href="http://en.wikipedia.org/wiki/Shine-Dalgarno_sequence">Shine-Dalgarno sequence</a> that ribosomes recognize.</p><p>The total set of genes in an organism is known as its <a title="Genome" href="http://en.wikipedia.org/wiki/Genome">genome</a>. An organism's <a title="Genome size" href="http://en.wikipedia.org/wiki/Genome_size">genome size</a> is generally lower in <a title="Prokaryote" href="http://en.wikipedia.org/wiki/Prokaryote">prokaryotes</a>, both in number of <a title="Base pair" href="http://en.wikipedia.org/wiki/Base_pair">base pairs</a> and number of genes, than even single-celled <a title="Eukaryote" href="http://en.wikipedia.org/wiki/Eukaryote">eukaryotes</a>. 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 <a title="Amoeba" href="http://en.wikipedia.org/wiki/Amoeba">amoeba</a> <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"><a title="" href="http://en.wikipedia.org/wiki/Gene#_note-Cavalier-Smith">[5]</a></sup> The estimated number of genes in the <a title="Human genome" href="http://en.wikipedia.org/wiki/Human_genome">human genome</a> has been repeatedly revised downward since the completion of the <a title="Human Genome Project" href="http://en.wikipedia.org/wiki/Human_Genome_Project">Human Genome Project</a>; 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_20045">[8]</a><br /sup></p><p><span class="mw-headline"><font size="5">History</font></span></p>
<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>
<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><a id="Further_reading" name="Further_reading"></a></p>
<h2><span class="editsection">[<a title="Edit section: Further reading" href="http://en.wikipedia.org/w/index.php?title=Gene&action=edit&section=23">edit</a>]</span> <span class="mw-headline">Further reading</span></h2>
<ul>
<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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<p><a id="External_links" name="External_links"></a></p>
<h2><span class="editsection">[<a title="Edit section: External links" href="http://en.wikipedia.org/w/index.php?title=Gene&action=edit&section=24">edit</a>]</span> <span class="mw-headline">External links</span></h2>
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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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