Transgenerational epigenetic inheritance: how important is it?
Nature Reviews Genetics 14, 228-235 (March 2013)
Ueli Grossniklaus, William G. Kelly, Anne C. Ferguson-Smith, Marcus Pembrey & Susan Lindquist
Many of these parental (and sometimes grandparental) effects will not have an epigenetic basis.
This is particularly important when considering environmentally induced effects, for which an epigenetic basis can be inferred only if they last over multiple generations.
In a pregnant mammal, for instance, not only are the mother and fetus exposed to the same environmental influences but so are the fetus’s primordial germ cells, which will eventually produce the grandchildren.
For instance, expression of the methylation-sensitive, metastable agouti viable yellow (Avy) allele, which determines mouse coat colour and shows meiotic epigenetic inheritance, is modulated by the animal’s diet. The specific dietary conditions in which a pregnant female is raised can change the inheritance pattern over two generations, but this change gets lost in the third generation.
Thus, while this specific diet leads to parental and grandparental effects, the induced epigenetic changes are not transgenerationally inherited.
… It is worth noting that most of the factors that guide these epigenetic processes in C. elegans have orthologues in most eukaryotes, so it is certainly plausible that these routes to epigenetic inheritance exist in many organisms.