In 1994, as cited in the same issue of Science, Robin Holliday voiced a commonly apprehended drift in meaning, and redefined epigenetic as "Nuclear inheritance which is not based on differences in DNA sequence." These two memes are freely circulating and can cause muddle or mischief mainly when they recombine, namely when epigenetic-H is automatically applied to epigenetic-W.
For example, epigenetic-H might be taken to imply that the developmental modulation of cell phenotype is always nuclear but not sequence-related (what I will suggest be called epinucleic). But there are many epigenetic-W (read developmental) processes that do depend on sequence-related changes, such as cellular senescence following upon telomere-shortening, or immunocyte diversification from promiscuous recombination and mutagenesis. Cytoplasmic heredity is still contentious, but it has strong foundations in studies of protozoa. If nuclear in epigenetic-H means chromosomal, then we have innumerable exceptions in the role of mitochondria and other endocellular plasmids and ...
