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An early version was proposed, among the founding statements in embryology, by Karl Ernst von Baer and popularized by Ernst Haeckel.A radical epigenetic view (physiological epigenesis) was developed by Paul Wintrebert.
Epigenetics often refers to changes in a chromosome that affect gene activity and expression, but can also be used to describe any heritable phenotypic change that does not derive from a modification of the genome, such as prions.The term also refers to the changes themselves: functionally relevant changes to the genome that do not involve a change in the nucleotide sequence.Examples of mechanisms that produce such changes are DNA methylation and histone modification, each of which alters how genes are expressed without altering the underlying DNA sequence.The consensus definition now requires a trait to be heritable for it to be considered epigenetic.
A consensus definition of the concept of epigenetic trait as "stably heritable phenotype resulting from changes in a chromosome without alterations in the DNA sequence" was formulated at a Cold Spring Harbor meeting in 2008, From the generic meaning, and the associated adjective epigenetic, C. Waddington coined the term epigenetics in 1942 as pertaining to epigenesis, in parallel to Valentin Haecker's 'phenogenetics' (Phänogenetik).
The NIH "Roadmap Epigenomics Project", ongoing as of 2016, uses the following definition: "For purposes of this program, epigenetics refers to both heritable changes in gene activity and expression (in the progeny of cells or of individuals) and also stable, long-term alterations in the transcriptional potential of a cell that are not necessarily heritable." In 2008, a consensus definition of the epigenetic trait, "stably heritable phenotype resulting from changes in a chromosome without alterations in the DNA sequence", was made at a Cold Spring Harbor meeting.