Fig. 2.

Cycle of methylation through mammalian development. Mammalian cells undergo two major waves of demethylation. The first wave occurs during the pre-implantation period when most methylation, including most sex-specific methylation is cleared, with the exception of the imprinted gDMRs. A second wave of demethylation occurs in PGCs when all methylation is cleared, including gDMRs, except for certain repeats. The genome is then re-methylated in a sex specific manner and parental specific methylation at gDMRs is established