Epigenetics – an introductory overview

Epigenetics or imprinting refers to the process of ‘chemically’ marking the central A, C, G, T double-stranded DNA code. In the past several decades a deeper understanding has been gained of a wide range of mechanisms that have been invoked in biology for the purpose of regulating gene expression and dosage of protein products that are effectively translated and functional in the cells. We mostly carry two copies of a gene (one per non-sex chromosome inherited from each of our parents) in each of our somatic cells; however, some genes are required to have two functional copies in each cell, while others require no less than one copy, but are tolerant of more than one copy. There are very specific genes, often dealing with growth and development, which are, however, only ever needed in a single copy; any more or any less is problematic and even lethal. Epigenetics is the process of reversibly ‘marking’ genes, either driven by endogenous processes or through exposure to environmental factors, such that they may be effectively silenced. Human development requires an orderly and systematic means of switching on and off of genes; understandably, if there is a mutation affecting this process, it leads to disease, while exposure to chemicals or other experiential stimuli may have a similar effect. This review provides a broad outline of epigenetics and genetic imprinting on human and mammalian development and disease.