Epigenetic

The old and optimistic “one gene — one character” concept has long been invalidated by phenomena such as pleiotropy and polygeny, and for a generation now we have thought of genomic activity as a system of complex epigenetic interactions — an epigenetic landscape.

Every cell in the body contains the same DNA but epigenetic settings on cells in the bone and blood, for example, mean the tissues do very different jobs. The epigenetic consequences of a huge range of environmental factors are under investigation, from exposure to drugs, chemicals and hormones, to the impact of poor maternal care in infancy, and the likelihood that they are as hereditable as DNA.

It is now possible to define whole epigenomes, representing the totality of epigenetic marks in a given cell type. Epigenetic processes are essential for packaging and interpreting the genome, are fundamental to normal development and are increasingly recognized as being involved in human disease.

As one celebrated example, if you're a baby rat growing up with an atypically inattentive mother, epigenetic changes in the regulation of one gene in your hippocampus will make it harder for you to recover from stress as an adult.