Epigenetics refers to alterations in gene expression that cannot be explained by changes in the sequence of deoxyribonucleic acid.

Epigenetic traits have significant economic and medical relevance. For example, during the last few years it has become clear that epigenetics has an essential role in the mechanism by which the expression of genes is turned on and off. Selective temporal gene expression is vital for the normal development of cells and organelles in both animals and plants, and the response of genomes to environmental stress. In addition, expression of certain genes at an inappropriate time is known to play a critical role in certain human diseases. The increased understanding of epigenetic mechanisms should reveal more of the functioning of genes.

The concept of epigenetic arose with the increased awareness that active and inactive genes having the same DNA sequence can be passed from parent cells to progeny cells...