The Greek prefix epi- can signify upon, on, over, near, at, before, and after. Most of those could apply to its use in the term ‘epigenetics’ — particularly the last of them. It is some 14 years, almost to the day, that Nature published the draft sequence of the human genome. Now, in this issue, we publish results from a subsequent study on the non-genetic modifications to the genome — epigenetic modifications — that crucially determine which genes are expressed by which cell type, and when.
It is hard to think of any branch of human biology that has not benefited from the human genome sequence. Its legacy has perhaps been most notable in advances in our appreciation of the part that genetics and genetic variation play in the normal functioning of a human body and in disease. But despite the progress, each question that the genome helps to answer throws up further questions. Much remains to be understood about how genetic information is interpreted by the individual cells in our body.
This is where epigenetics comes in. Upon the genome, on the genome, over the genome — take your pick — epigenetics collectively describes changes in the regulation of gene expression that can be passed on to a cell’s progeny but are not due to changes to the nucleotide sequence of the gene.