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<h2>Definition : Heritable changes in gene activity and expression that occur without alteration in DNA sequence</h2>
<h2>Different cells control switching on and off in different genes</h2>
<h2>Two well-known epigenetic modifications</h2>
<olul>
<li>Chemical modification to the cytosine residues of DNA (DNA methylation)</li>
</ul>
<p><img src="http://www.ks.uiuc.edu/Research/methylation/dna_mdna.png" /></p>
<ul>
<li>Histone modification</li>
</olul>
<h2>Why is it important ? >>> Epigenetic modifications regulate gene activity and expression during development and differentiation, or in response to environmental stimuli</h2>
<h4>We could increase the mRNA of <em>ADH</em> and then make ADH more than usual when we drink much </h4>
<h2>Only 2 % of human genome encodes protein and the other 98% controls gene expression by epigenetic mechanism.</h2>
<p> </p>
