Epigenetics

In <a href="/facts/Biology/1M1ee3pB">biology</a>, epigenetics is the study of <a href="/facts/Heritability/REQ3CfRe">heritable traits</a>, or a stable change of cell function, that happen without changes to the <a href="/facts/DNA_sequence/hsPsNCQW">DNA sequence</a>. The <a href="/facts/Ancient_Greek/LIK7NlUh">Greek</a> prefix epi- (ἐπι- "over, outside of, around") in epigenetics implies features that are "on top of" or "in addition to" the traditional (DNA sequence based) <a href="/facts/Gene/e1swwPY6">genetic</a> mechanism of inheritance. Epigenetics usually involves a change that is not erased by cell division, and affects the <a href="/facts/Regulation_of_gene_expression/9N4G341I">regulation of gene expression</a>. Such effects on <a href="/facts/Cell_(biology)/bLM9UQvy">cellular</a> and <a href="/facts/Physiology/fh25y2pQ">physiological</a> <a href="/facts/Phenotypic_trait/seYSUTul">phenotypic traits</a> may result from <a href="/facts/Environment_(biophysical)/PNzMrGrz">environmental</a> factors, or be part of normal development. Epigenetic factors can also lead to cancer.
The term also refers to the mechanism of changes: functionally relevant alterations to the <a href="/facts/Genome/31Sm08JT">genome</a> that do not involve mutation of the <a href="/facts/Nucleotide_sequence/qAf4kTee">nucleotide sequence</a>. Examples of mechanisms that produce such changes are <a href="/facts/DNA_methylation/npoRhsnX">DNA methylation</a> and <a href="/facts/Histone_modification/krb5VJfp">histone modification</a>, each of which alters how genes are expressed without altering the underlying <a href="/facts/DNA/nB89Iauz">DNA</a> sequence. Further, non-coding RNA sequences have been shown to play a key role in the regulation of gene expression. Gene expression can be controlled through the action of <a href="/facts/Repressor_protein/qGBBQwqS">repressor proteins</a> that attach to <a href="/facts/Silencer_(DNA)/ygy7GUNy">silencer</a> regions of the DNA. These epigenetic changes may last through <a href="/facts/Cell_division/n5MrunWj">cell divisions</a> for the duration of the cell's life, and may also last for multiple generations, even though they do not involve changes in the underlying DNA sequence of the organism; instead, non-genetic factors cause the organism's genes to behave (or "express themselves") differently.
One example of an epigenetic change in <a href="/facts/Eukaryotic/SkwyPLMA">eukaryotic</a> biology is the process of <a href="/facts/Cellular_differentiation/bCVqUG7w">cellular differentiation</a>. During <a href="/facts/Morphogenesis/zHJh8Eae">morphogenesis</a>, <a href="/facts/Totipotent/81323LbR">totipotent</a> <a href="/facts/Stem_cells/qgB9dFrI">stem cells</a> become the various <a href="/facts/Pluripotent/81323LbR">pluripotent</a> <a href="/facts/Cell_line/X4fClRIf">cell lines</a> of the <a href="/facts/Embryo/9QHnLVLN">embryo</a>, which in turn become fully differentiated cells. In other words, as a single fertilized <a href="/facts/Egg_cell/gJyW3W3W">egg cell</a> – the <a href="/facts/Zygote/mSu2xMWA">zygote</a> – continues to <a href="/facts/Mitosis/ExxrSUs8">divide</a>, the resulting daughter cells change into all the different cell types in an organism, including <a href="/facts/Neurons/G7CyTVdH">neurons</a>, <a href="/facts/Muscle_cells/cP7Jea3q">muscle cells</a>, <a href="/facts/Epithelium/ecKHcHC3">epithelium</a>, <a href="/facts/Endothelium/L4ENFVnw">endothelium</a> of <a href="/facts/Blood_vessels/FG3GjPNW">blood vessels</a>, etc., by activating some genes while inhibiting the expression of others.

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Epigenetics