Genomic imprinting: control of gene expression by epigenetic inheritance.

One parental copy of an imprinted gene is invariably expressed during development. The characteristic of the heritable epigenetic germline imprint remains elusive, but recent evidence stresses the necessity for additional post-zygotic epigenetic modifications to account for this temporal and tissue-specific mono-allelic expression. Preliminary insight into a diversity of post-zygotic control mechanisms is beginning to emerge.