Imprinting

Imprinting is a term used to describe two very distinct processes. Genomic imprinting is an epigenetic chromosomal modification that describes the preferential expression of a specific parental form of a gene (allele). Imprinting is also a term used in the behavioral science to describe a learning process during which a younger animal identifies with, and adopts behaviors exhibited by, other animals, usually of the same species.

Impact of genomic imprinting

In most cases genomic imprinting is a normal process and has no affect on the normal individual. However, imprinted genes are involved in the development of some genetic disorders and in cancer.

Imprinted genes are involved in the development of some cancers. The imprinted fetal growth factor gene, IGF2, is commonly expressed in cancers such as Wilms tumor of the kidney, and cancers of the breast, lung, liver, and colon. In these cancers the maternal IGF2 imprint has been lost and both gene alleles are expressed (bi-allelic expression), this is termed "relaxation of imprinting."

There are many theories for why genomic imprinting exists. One of the most favored (in accord with the most current data), proposed by David Haig (the Haig Hypothesis), suggests that imprinting is a form of genetic reproductive conflict between the sexes each vying for a different reproductive outcome. Males desire large offspring males, so they over-express growth factors such as the paternally expressed fetal growth factor IGF2. However, females needing to limit fetal growth to ensure their successful birth have repressed growth factor expression by imprinting the gene.