Figure 2: Schematic representation of heritable epigenetic change in the early embryo. The susceptible period is the developmental stage at which changes in histone modification levels, perhaps at only some genes, induced by environmental disruptors, can be passed on, through mitosis, to subsequent cell generations. If induced changes are transmitted to the primordial germ cells (PGCs) and hence into the gametes, they could be transmitted through the germ line to the next generation.