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<p><strong>Developmental biology</strong> is the study of the process by which organisms grow and develop. Modern developmental biology studies the genetic control of <font color="#0066cc">cell growth</font>, <font color="#0066cc">differentiation</font> and "<font color="#0066cc">morphogenesis</font>," which is the process that gives rise to <font color="#0066cc">tissues</font>, <font color="#0066cc">organs</font> and <font color="#0066cc">anatomy</font>. <font color="#0066cc">Embryology</font> is a subfield, the study of organisms between the one-cell stage (generally, the <font color="#0066cc">zygote</font>) and the end of the embryonic stage, which is <em>not</em> necessarily the beginning of a free living organism. Embryology was originally a more descriptive science until the <font color="#0066cc">20th century</font>. Embryology and developmental biology today deal with the various steps necessary for the correct and complete formation of the <font color="#0066cc">body</font> of a living organism.</p><p>The related field of <font color="#0066cc">evolutionary developmental biology</font> was formed largely in the <font color="#0066cc">1990s</font> and is a <font color="#0066cc">synthesis</font> of findings from molecular developmental biology and <font color="#0066cc">evolutionary biology</font> which considers the diversity of organismal form in an evolutionary context.</p><p>The findings of developmental biology can help to understand developmental malfunctions such as <font color="#0066cc">chromosomal aberrations</font>, for example, <font color="#0066cc">Down syndrome</font>. An understanding of the specialization of <font color="#0066cc">cells</font> during embryogenesis may yield information on how to specialize <font color="#0066cc">stem cells</font> to specific tissues and organs, which could lead to the specific <font color="#0066cc">cloning</font> of organs for medical purposes. Another biologically important process that occurs during development is <font color="#0066cc">apoptosis</font> - programmed cell death or "suicide". For this reason, many developmental models are used to elucidate the <font color="#0066cc">physiology</font> and molecular basis of this cellular process. Similarily, a deeper understanding of developmental biology can foster greater progress in the treatment of <font color="#0066cc">congenital</font> disorders and diseases, e.g. studying <font color="#0066cc">human sex determination</font> can lead to treatment for disorders such as <font color="#0066cc">congenital adrenal hyperplasia</font>.</p><p><br /></p><script type="text/javascript">//<![CDATA[ if (window.showTocToggle) { var tocShowText = "show"; var tocHideText = "hide"; showTocToggle(); } //]]></script><p><a id="Molecular_mechanisms_of_development" name="Molecular_mechanisms_of_development"></a></p><h2><span class="mw-headline">Molecular mechanisms of development</span></h2><p>During the second half of the 20th century the types of molecules involved in embryonic development were identified. <a title="Transcription factor" href="http://en.wikipedia.org/wiki/Transcription_factor"><font color="#0066cc">Transcription factors</font></a> are the key regulators of which <a title="Gene" href="http://en.wikipedia.org/wiki/Gene"><font color="#0066cc">genes</font></a> are expressed in cells. Transcriptional control in the various differentiated cell types allows each <a title="Cell type" href="http://en.wikipedia.org/wiki/Cell_type"><font color="#0066cc">type of cell</font></a> (epithelial, muscle, neuron, etc) to express different amounts of the possible proteins. The transcription factors are regulated by <a title="Signal transduction" href="http://en.wikipedia.org/wiki/Signal_transduction"><font color="#0066cc">signal transduction</font></a> pathways that relay signals from outside of cells to the cell nucleus. Signal transduction pathways often involve <a title="Receptor (biochemistry)" href="http://en.wikipedia.org/wiki/Receptor_%28biochemistry%29"><font color="#0066cc">receptors</font></a>, receptor <a title="Ligand" href="http://en.wikipedia.org/wiki/Ligand#Biochemical_ligands"><font color="#0066cc">ligands</font></a> and enzymes such as <a title="Protein kinase" href="http://en.wikipedia.org/wiki/Protein_kinase"><font color="#0066cc">protein kinases</font></a>. One key class of genes that are differentially regulated by transcription factors in different cell types are genes for <a title="Cell adhesion" href="http://en.wikipedia.org/wiki/Cell_adhesion"><font color="#0066cc">cell adhesion</font></a> proteins. Cell adhesion proteins are among the key regulators of <a title="Morphogenesis" href="http://en.wikipedia.org/wiki/Morphogenesis"><font color="#0066cc">morphogenesis</font></a>. Functions of these various proteins in development are often elucidated experimentally using <a title="Gene knockdown" href="http://en.wikipedia.org/wiki/Gene_knockdown"><font color="#0066cc">gene knockdown</font></a> techniques in embryos.</p><p><a id="Concepts_in_developmental_biology" name="Concepts_in_developmental_biology"></a></p><h2><span class="mw-headline">Concepts in developmental biology</span></h2><dl><dd><a title="Allantois" href="http://en.wikipedia.org/wiki/Allantois"><font color="#0066cc">allantois</font></a>, <a title="Amnion" href="http://en.wikipedia.org/wiki/Amnion"><font color="#0066cc">amnion</font></a>, <a title="Blastocyst" href="http://en.wikipedia.org/wiki/Blastocyst"><font color="#0066cc">blastocyst</font></a>, <a title="Blastomere" href="http://en.wikipedia.org/wiki/Blastomere"><font color="#0066cc">blastomere</font></a>, <a title="Blastula" href="http://en.wikipedia.org/wiki/Blastula"><font color="#0066cc">blastula</font></a>, <a class="new" title="Blastulation" href="http://en.wikipedia.org/w/index.php?title=Blastulation&action=edit"><font color="#0066cc">blastulation</font></a>, <a title="Chorion" href="http://en.wikipedia.org/wiki/Chorion"><font color="#0066cc">chorion</font></a>, <a title="Pupa" href="http://en.wikipedia.org/wiki/Pupa"><font color="#0066cc">chrysalis</font></a>, <a title="Cleavage (embryo)" href="http://en.wikipedia.org/wiki/Cleavage_%28embryo%29"><font color="#0066cc">cleavage</font></a>, <a title="Embryo" href="http://en.wikipedia.org/wiki/Embryo"><font color="#0066cc">embryo</font></a>, <a title="Embryogenesis" href="http://en.wikipedia.org/wiki/Embryogenesis"><font color="#0066cc">embryogenesis</font></a>, <a class="new" title="Embryogeny" href="http://en.wikipedia.org/w/index.php?title=Embryogeny&action=edit"><font color="#0066cc">embryogeny</font></a>, <a title="Embryology" href="http://en.wikipedia.org/wiki/Embryology"><font color="#0066cc">embryology</font></a>, <a class="new" title="Extra-embryonic membrane" href="http://en.wikipedia.org/w/index.php?title=Extra-embryonic_membrane&action=edit"><font color="#0066cc">extra-embryonic membrane</font></a>, <a title="Fetus" href="http://en.wikipedia.org/wiki/Fetus"><font color="#0066cc">fetus</font></a>, <a title="Gastrula" href="http://en.wikipedia.org/wiki/Gastrula"><font color="#0066cc">gastrula</font></a>, <a title="Gastrulation" href="http://en.wikipedia.org/wiki/Gastrulation"><font color="#0066cc">gastrulation</font></a>, <a title="Germ layer" href="http://en.wikipedia.org/wiki/Germ_layer"><font color="#0066cc">germ layer</font></a>, <a title="Germ plasm" href="http://en.wikipedia.org/wiki/Germ_plasm"><font color="#0066cc">germ plasm</font></a>, <a title="Germination" href="http://en.wikipedia.org/wiki/Germination"><font color="#0066cc">germination</font></a>, <a title="Induction (biology)" href="http://en.wikipedia.org/wiki/Induction_%28biology%29"><font color="#0066cc">induction</font></a>, <a title="Adolescence" href="http://en.wikipedia.org/wiki/Adolescence"><font color="#0066cc">juvenile</font></a>, <a title="Larva" href="http://en.wikipedia.org/wiki/Larva"><font color="#0066cc">larva</font></a>, <a title="Maternal effect" href="http://en.wikipedia.org/wiki/Maternal_effect"><font color="#0066cc">maternal effect</font></a>, <a title="Metamorphosis (biology)" href="http://en.wikipedia.org/wiki/Metamorphosis_%28biology%29"><font color="#0066cc">metamorphosis</font></a>, <a title="Genome" href="http://en.wikipedia.org/wiki/Genome"><font color="#0066cc">genome</font></a>, <a title="Morphogenesis" href="http://en.wikipedia.org/wiki/Morphogenesis"><font color="#0066cc">morphogenesis</font></a>, <a title="Morula" href="http://en.wikipedia.org/wiki/Morula"><font color="#0066cc">morula</font></a>, <a title="Neoteny" href="http://en.wikipedia.org/wiki/Neoteny"><font color="#0066cc">neoteny</font></a>, <a title="Neural development" href="http://en.wikipedia.org/wiki/Neural_development"><font color="#0066cc">neural development</font></a>, <a title="Nymph (biology)" href="http://en.wikipedia.org/wiki/Nymph_%28biology%29"><font color="#0066cc">nymph</font></a>, <a title="Ontogeny" href="http://en.wikipedia.org/wiki/Ontogeny"><font color="#0066cc">ontogeny</font></a>, <a class="new" title="Oosperm" href="http://en.wikipedia.org/w/index.php?title=Oosperm&action=edit"><font color="#0066cc">oosperm</font></a>, <a class="new" title="Ovism" href="http://en.wikipedia.org/w/index.php?title=Ovism&action=edit"><font color="#0066cc">ovism</font></a>, <a title="Paedogenesis" href="http://en.wikipedia.org/wiki/Paedogenesis"><font color="#0066cc">paedogenesis</font></a>, <a title="Pangenesis" href="http://en.wikipedia.org/wiki/Pangenesis"><font color="#0066cc">pangenesis</font></a>, <a title="Phylogeny" href="http://en.wikipedia.org/wiki/Phylogeny"><font color="#0066cc">phylogeny</font></a>, <a title="Primordium" href="http://en.wikipedia.org/wiki/Primordium"><font color="#0066cc">primordium</font></a>, <a title="Pupa" href="http://en.wikipedia.org/wiki/Pupa"><font color="#0066cc">pupa</font></a>, <a title="Rudiment (biology)" href="http://en.wikipedia.org/wiki/Rudiment_%28biology%29"><font color="#0066cc">rudiment</font></a>, <a title="Seed" href="http://en.wikipedia.org/wiki/Seed"><font color="#0066cc">seed</font></a>, <a title="Self-organization" href="http://en.wikipedia.org/wiki/Self-organization"><font color="#0066cc">self-organization</font></a>, <a title="Teratology" href="http://en.wikipedia.org/wiki/Teratology"><font color="#0066cc">teratology</font></a>, <a title="Zygote" href="http://en.wikipedia.org/wiki/Zygote"><font color="#0066cc">zygote</font></a> </dd></dl><p><a id="Developmental_model_organisms" name="Developmental_model_organisms"></a></p><h2><span class="mw-headline">Developmental model organisms</span></h2><p>Often used <a title="Model organism" href="http://en.wikipedia.org/wiki/Model_organism"><font color="#0066cc">model organisms</font></a> in developmental biology include the following:</p><ul> <li>Vertebrates <ul> <li>Zebrafish <em><a title="Danio rerio" href="http://en.wikipedia.org/wiki/Danio_rerio"><font color="#0066cc">Danio rerio</font></a></em> </li> <li>Medakafish <em><a title="Oryzias latipes" href="http://en.wikipedia.org/wiki/Oryzias_latipes"><font color="#0066cc">Oryzias latipes</font></a></em> </li> <li>Fugu <em><a title="Takifugu rubripes" href="http://en.wikipedia.org/wiki/Takifugu_rubripes"><font color="#0066cc">Takifugu rubripes</font></a></em> </li> <li><a title="Frog" href="http://en.wikipedia.org/wiki/Frog"><font color="#0066cc">Frogs</font></a> <em><a title="Xenopus laevis" href="http://en.wikipedia.org/wiki/Xenopus_laevis"><font color="#0066cc">Xenopus laevis</font></a></em> </li> <li>Chicken <em><a title="Gallus gallus" href="http://en.wikipedia.org/wiki/Gallus_gallus"><font color="#0066cc">Gallus gallus</font></a></em> </li> <li>Mouse <em><a title="Mus musculus" href="http://en.wikipedia.org/wiki/Mus_musculus"><font color="#0066cc">Mus musculus</font></a></em> (<a title="Mammalian embryogenesis" href="http://en.wikipedia.org/wiki/Mammalian_embryogenesis"><font color="#0066cc">Mammalian embryogenesis</font></a>) </li> </ul> </li> <li>Invertebrates <ul> <li><a title="Lancelet" href="http://en.wikipedia.org/wiki/Lancelet"><font color="#0066cc">Lancelet</font></a> <em>Branchiostoma lanceolatum</em> </li> <li><a title="Tunicates" href="http://en.wikipedia.org/wiki/Tunicates"><font color="#0066cc">Tunicates</font></a> </li> <li><a title="Sea urchin" href="http://en.wikipedia.org/wiki/Sea_urchin"><font color="#0066cc">Sea urchin</font></a> </li> <li>Round worm <em><a title="Caenorhabditis elegans" href="http://en.wikipedia.org/wiki/Caenorhabditis_elegans"><font color="#0066cc">Caenorhabditis elegans</font></a></em> </li> <li>Fruit fly <em><a title="Drosophila melanogaster" href="http://en.wikipedia.org/wiki/Drosophila_melanogaster"><font color="#0066cc">Drosophila melanogaster</font></a></em> (<a title="Drosophila embryogenesis" href="http://en.wikipedia.org/wiki/Drosophila_embryogenesis"><font color="#0066cc">Drosophila embryogenesis</font></a>) </li> </ul> </li> <li>Plants (<a title="Plant embryogenesis" href="http://en.wikipedia.org/wiki/Plant_embryogenesis"><font color="#0066cc">Plant embryogenesis</font></a>) <ul> <li><em><a title="Arabidopsis thaliana" href="http://en.wikipedia.org/wiki/Arabidopsis_thaliana"><font color="#0066cc">Arabidopsis thaliana</font></a></em> </li> <li><a title="Maize" href="http://en.wikipedia.org/wiki/Maize"><font color="#0066cc">Maize</font></a> </li> <li><a title="Snapdragon" href="http://en.wikipedia.org/wiki/Snapdragon"><font color="#0066cc">Snapdragon</font></a> </li> </ul> </li></ul><p><a id="Developmental_systems_biology" name="Developmental_systems_biology"></a></p><h2><span class="mw-headline">Developmental systems biology</span></h2><p>Computer simulation of multicellular development is a research methodology to understand the function of the very complex processes involved in the development of organisms. This includes simulation of cell signaling, multicell interactions and regulatory genomic networks in development of multicellular structures and processes (see <a title="List of publications in biology" href="http://en.wikipedia.org/wiki/List_of_publications_in_biology#Developmental_biology"><em><font color="#0066cc">Biological Physics of the Developing Embryo</font></em></a>). <em><a title="Genomes" href="http://en.wikipedia.org/wiki/Genomes#Minimal_genomes"><font color="#0066cc">Minimal genomes</font></a></em> for minimal multicellular organisms may pave the way to understand such complex processes <em>in vivo</em>.</p><p><a id="See_also" name="See_also"></a></p><h2><span class="mw-headline">See also</span></h2><ul> <li><a title="Altricial" href="http://en.wikipedia.org/wiki/Altricial"><font color="#0066cc">altricial</font></a> and <a title="Precocial" href="http://en.wikipedia.org/wiki/Precocial"><font color="#0066cc">precocial</font></a> </li> <li><a title="Auxology" href="http://en.wikipedia.org/wiki/Auxology"><font color="#0066cc">auxology</font></a> </li> <li><a title="Embryogenesis" href="http://en.wikipedia.org/wiki/Embryogenesis"><font color="#0066cc">embryogenesis</font></a> </li> <li><a title="List of publications in biology" href="http://en.wikipedia.org/wiki/List_of_publications_in_biology#Developmental_biology"><font color="#0066cc">Important publications in developmental biology</font></a> </li> <li><a title="Morphogenesis" href="http://en.wikipedia.org/wiki/Morphogenesis"><font color="#0066cc">morphogenesis</font></a> </li></ul><p><a id="Sources" name="Sources"></a></p><h2><span class="mw-headline">Sources</span></h2><ul> <li><a class="external text" title="http://www.ncbi.nlm.nih.gov:80/books/bv.fcgi?call=bv.View..ShowTOC&rid=dbio.TOC&depth=2" href="http://www.ncbi.nlm.nih.gov/books/bv.fcgi?call=bv.View..ShowTOC&rid=dbio.TOC&depth=2" rel="nofollow"><font color="#0066cc">Developmental Biology</font></a> by Scott Gilbert (online textbook) </li> <li><a class="external text" title="http://www.sdbonline.org/virtual_library.php" href="http://www.sdbonline.org/virtual_library.php" rel="nofollow"><font color="#0066cc">Virtual Library - Developmental Biology</font></a> </li> <li><a class="external text" title="http://www.bionews.in/index.php/archives/category/developmental-biology/" href="http://www.bionews.in/index.php/archives/category/developmental-biology/" rel="nofollow"><font color="#0066cc">Latest Developmental Biology News</font></a> </li> <li><a class="external text" title="http://www.eb.tuebingen.mpg.de/" href="http://www.eb.tuebingen.mpg.de/" rel="nofollow"><font color="#0066cc">Max Planck Institute for Developmental Biology</font></a> </li> <li><a class="external text" title="http://en.developmentalbiology.de/" href="http://en.developmentalbiology.de/" rel="nofollow"><font color="#0066cc">Developmental Biology of Plants and Animals</font></a> </li></ul>