epigenetics: a standalone construct

The developmental biologist Conrad H. Waddington coined the term in 1942, joining the Greek epi (over, above) to genetics to name the layer of processes that sits above the genes and steers how a fertilised egg develops into a differentiated organism. In the modern meaning, worked out from the 1970s onward by Arthur Riggs, Robin Holliday, and others and given a shared operational definition by Berger and colleagues in 2009, epigenetics is the study of heritable changes in gene activity that are not caused by changes in the underlying DNA sequence, changes carried instead by chemical marks such as DNA methylation and modifications to the histone proteins that spool and package DNA. These marks switch genes on or off and can persist as a cell divides, and in some lines pass to offspring, which is how genetically identical cells become distinct tissues and how one genome can support many stable patterns of expression. What makes the construct a landmark is its scope: it accounts for durable differences in the phenotype that classical genetics, reading only the DNA sequence, cannot explain, and it ties molecular mechanism to development, disease, and inheritance across every discipline that studies living cells.[1][2][3][4]

Unit

A body of study, and the class of heritable gene-regulatory states it describes, sitting above the DNA sequence

Recovery means

Not applicable

Measured by

Identified by assays of DNA methylation, histone modification, and chromatin state, such as bisulfite sequencing and chromatin immunoprecipitation, that map regulatory marks without altering the DNA sequence