The diagram illustrates the fate of a chromosome carrying two genes, A and B, which are subject to imprinting: A is imprinted in the female germline, B is imprinted in the male germline, as indicated by asterisks. As a result, in diploid somatic cells A is imprinted when present on a maternally inherited chromosome and B is imprinted when present on a paternally inherited chromosome. An individual chromosome may pass through the male and female germlines in successive generations: a man may transmit a chromosome inherited from his mother and a woman can transmit a chromosome inherited from her father, as indicated by the gametes in the left panel. As a result, there must be a mechanism whereby the old imprint is erased from the germline prior to establishing a new sex-specific imprint.