from Jennifer E. Cropley and Catherine M. Suter writing in Epigenetics: A Reference Manual:
Epigenetic states are faithfully inherited through mitotic cell division, but are generally cleared and reset on passage through the mammalian germline. But this clearing of epigenetic marks is not always complete, leading to transgenerational inheritance of epigenotype. Transgenerational epigenetic inheritance has been demonstrated in several organisms, including mammals, and has been most comprehensively studied in mouse strains carrying variants of the agouti (Avy) and axin (AxinFu) alleles. The most prominent feature of transgenerational epigenetic inheritance is its non-Mendelian nature: not all offspring that inherit the genetic locus also inherit the parental epigenetic state. Transgenerational epigenetic inheritance is emerging as an important facet of mammalian biology. It may underlie the etiology of human diseases that display complex patterns of inheritance, including diabetes, mental illnesses and autoimmune diseases. As variable epigenetic states can be inherited on an invariant genotype, epigenetic variation may provide a substrate for Darwinian selection that is independent of genetic variation.
Further reading: Epigenetics: A Reference Manual