Genomic Imprinting: Common Threads Uniting Diverse Biological Systems.

Genomic imprinting is an epigenetic phenomenon in which chromosome behavior or gene expression depends on whether an allele was paternally or maternally inherited. Imprinting is commonly associated with a placenta or an analogous organ during embryo development; however, imprinting occurs in diverse species across animal and plant life, including those that lack a placenta. Common epigenetic modifications are associated with genome imprinting across these groups, although the exact mechanisms vary across taxa. There are also commonalities surrounding the evolutionary selection for imprinting. The most well-known hypothesis is parental conflict theory, which proposes that imprinting resolves conflict over the maternal allocation of resources to the developing embryo. Shared mechanisms and functions of imprinting across diverse groups suggest that parental epigenetic asymmetries may be an inherent characteristic of sexual reproduction in species where the sperm and egg differ in size and form.