Definition of "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.

1977 December, Rupert Riedl, “A Systems-Analytical Approach to Macro-Evolutionary Phenomena”, in The Quarterly Review of Biology, volume 52, number 4, page 352

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.

2010 November 6, “Sins of the Fathers”, in New Scientist

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.

2008 August 7, The American Association for Cancer Research Human Epigenome Task Force, European Union, Network of Excellence, Scientific Advisory Board, “Moving AHEAD with an international human epigenome project”, in Nature, volume 454, page 711