Epigenetics
<p >In <a href="http://en.wikipedia.org/wiki/Biology" title="Biology" >biology</a>, and specifically <a href="http://en.wikipedia.org/wiki/Genetics" title="Genetics" >genetics</a>, <b>epigenetics</b> is the study of heritable changes in <a href="http://en.wikipedia.org/wiki/Gene_expression" title="Gene expression" >gene expression</a> or cellular phenotype caused by mechanisms other than changes in the underlying <a href="http://en.wikipedia.org/wiki/DNA" title="DNA" >DNA</a> sequence – hence the name <i>epi-</i> (Greek: <i>επί</i>- over, above, outer) <i>-<a href="http://en.wikipedia.org/wiki/Genetics" title="Genetics" >genetics</a></i>. It refers to functionally relevant modifications to the genome that do not involve a change in the nucleotide sequence. Examples of such changes are <a href="http://en.wikipedia.org/wiki/DNA_methylation" title="DNA methylation" >DNA methylation</a> and <a href="http://en.wikipedia.org/wiki/Histone_modification" title="Histone modification" class="mw-redirect" >histone modification</a>, both of which serve to regulate gene expression without altering the underlying DNA sequence. Conclusive evidence supporting epigenetics show that these mechanisms can enable the effects of parents' experiences to be <a href="http://en.wikipedia.org/wiki/Heredity" title="Heredity" >passed down</a> to subsequent generations.</p>
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These changes may remain through <a href="http://en.wikipedia.org/wiki/Cell_(biology)" title="Cell (biology)" >cell</a> <a href="http://en.wikipedia.org/wiki/Mitosis" title="Mitosis" >divisions</a> for the remainder of the cell's life and may also last for multiple generations. However, there is no change in the underlying <a href="http://en.wikipedia.org/wiki/DNA" title="DNA" >DNA</a>sequence of the organism;<sup id="cite_ref-pmid17522671_0-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Epigenetics#cite_note-pmid17522671-0" >[1]</a></sup> instead, non-genetic factors cause the organism's genes to behave (or "express themselves") differently.<sup id="cite_ref-1" class="reference" ><a href="http://en.wikipedia.org/wiki/Epigenetics#cite_note-1" >[2]</a></sup></p>
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One example of epigenetic changes in <a href="http://en.wikipedia.org/wiki/Eukaryotic" title="Eukaryotic" class="mw-redirect" >eukaryotic</a> biology is the process of <a href="http://en.wikipedia.org/wiki/Cellular_differentiation" title="Cellular differentiation" >cellular differentiation</a>. During <a href="http://en.wikipedia.org/wiki/Morphogenesis" title="Morphogenesis" >morphogenesis</a>, <a href="http://en.wikipedia.org/wiki/Totipotent" title="Totipotent" class="mw-redirect" >totipotent</a> <a href="http://en.wikipedia.org/wiki/Stem_cells" title="Stem cells" class="mw-redirect" >stem cells</a> become the various <a href="http://en.wikipedia.org/wiki/Pluripotent" title="Pluripotent" class="mw-redirect" >pluripotent</a> <a href="http://en.wikipedia.org/wiki/Cell_line" title="Cell line" class="mw-redirect" >cell lines</a> of the <a href="http://en.wikipedia.org/wiki/Embryo" title="Embryo" >embryo</a>, which in turn become fully differentiated cells. In other words, a single fertilized egg cell – the <a href="http://en.wikipedia.org/wiki/Zygote" title="Zygote" >zygote</a> – changes into the many cell types including neurons, muscle cells, epithelium, endothelium of blood vessels, etc. as it continues to <a href="http://en.wikipedia.org/wiki/Mitosis" title="Mitosis" >divide</a>. It does so by activating some genes while inhibiting others.<sup id="cite_ref-pmid17522676_2-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Epigenetics#cite_note-pmid17522676-2" >[3]</a></sup></p>
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In 2011, it was demonstrated that the <a href="http://en.wikipedia.org/wiki/Methylation" title="Methylation" >methylation</a> of <a href="http://en.wikipedia.org/wiki/Messenger_RNA" title="Messenger RNA" >mRNA</a> has a critical role in human <a href="http://en.wikipedia.org/wiki/Energy_balance_(biology)" title="Energy balance (biology)" >energy homeostasis</a>. Obesity associated <a href="http://en.wikipedia.org/wiki/FTO_gene" title="FTO gene" >FTO gene</a> is shown to be able to demethylate<a href="http://en.wikipedia.org/wiki/N6-methyladenosine" title="N6-methyladenosine" class="mw-redirect" >N6-methyladenosine</a> in RNA. This opened the related field of RNA epigenetics.<sup id="cite_ref-3" class="reference" ><a href="http://en.wikipedia.org/wiki/Epigenetics#cite_note-3" >[4]</a></sup><sup id="cite_ref-4" class="reference" ><a href="http://en.wikipedia.org/wiki/Epigenetics#cite_note-4" >[5]</a></sup></p>