Transgenerational epigenetic memory. The soma (oval shapes) and germlines (diamonds) of a developing embryo are depicted. A transient environmental insult, or transient loss or ectopic activation of an epigenetic ‘modifier’ (lightning symbol) can create a change in the chromatin architecture in the genome (red pattern). If change in chromatin occurs in the developing soma (right side), it may be inherited though cell division, but the change is (usually) limited to somatic lineages. If the chromatin is altered in the germline (left side), it may become stabilized, and a phenotypic alteration in the soma or germline may be observed in the offspring for multiple generations. The ‘epiallele’ often stochastically reverts to the original chromatin structure, resulting in a reversion to the original ancestral phenotype.