Fig. 1.

Modes of epigenetic inheritance. Phenotypes observed in F1 offspring of males (A) or females (B) prior to mating represent intergenerational effects, while effects observed in F2 and beyond are considered as transgenerational. (C) When a pregnant female is exposed to a drug, her fetus (F1) and its developing germ-line (F2) will be directly be exposed to the drug and therefore phenotypes observed in F1 and F2 offspring represent intergenerational effects. The F3 generation is the first representing true transgenerational epigenetic inheritance following in utero drug exposure. Red stars represent germ cells that were directly exposed to drug. Green stars represent germ cells that developed in the absence of direct drug exposure.