Epigenetics
In biology, epigenetics is the study of cellular and
physiological traits that are not caused by changes in the
DNA sequence.
Epigenetics describes the study of stable, long-term alterations
in the transcriptional potential of a cell. Some of those
alterations are heritable. Unlike simple genetics based on
changes to the DNA sequence (the genotype), the changes in gene
expression or cellular phenotype of epigenetics have other
causes, thus use of the term epi-genetics.
The term also refers to the changes themselves: functionally
relevant changes to the genome that do not involve a change in
the nucleotide sequence. Examples of mechanisms that produce such
changes are DNA methylation and histone modification, each of
which alters how genes are expressed without altering the
underlying DNA sequence. Gene expression can be controlled
through the action of repressor proteins that attach to silencer
regions of the DNA. These epigenetic changes may last through
cell divisions 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 eukaryotic biology is the
process of cellular differentiation. During Morphogenesis,
totipotent stem cells become the various pluripotent cell lines
of the embryo, which in turn become fully differentiated cells.
In other words, as a single fertilized egg cell – the zygote –
continues to divide, the resulting daughter cells change into all
the different cell types in an organism (including neurons,
muscle cells, epithelium, endothelium of blood vessels, etc.) by activating
some genes while inhibiting the expression of others.
Linguistic derivation
The term Epigenetics is derived from the ancient Greek
prefix epi (επί-) meaning "over, outside of, around, on
top of" and the word genetics from genesis
(γένεσις) meaning "origin", "source", or "birth".