“An epigenetic trait is a stably heritable phenotype resulting from changes in a chromosome without alterations in the DNA sequence.”
How this state is initiated, maintained and inherited is what constitutes the operational definition of epigenetics and an exciting topic at present.
The authors propose that there are three categories of signals that lead to the establishment of a stably heritable epigenetic state:
1) “Epigenator,” which includes an environmental cue and the intracellular pathways that can lead to an epigenetic phenotype;
2)“Epigenetic Initiator”, which responds to the Epigenator and mediates the establishment of a local chromatin context at a precise location and
3) “Epigenetic Maintainer”, which sustains the epigenetic chromatin state, in the first and subsequent generations, but is not sufficient to initiate it.