imprinted gene

Most genes work like a pair of identical light switches, where either copy can turn the light on. An imprinted gene is different: only one switch is wired to work, and which one depends on whether the copy came from your mother or your father.

Concretely, an imprinted gene is expressed from just one parental allele while the other is kept silent by an epigenetic mark, usually DNA methylation laid down during egg or sperm formation. A gene silenced when inherited from the mother is called maternally imprinted; one silenced when inherited from the father is paternally imprinted.

Because only a single copy is active, imprinted genes have no backup. A mutation, deletion, or faulty mark on the active copy can cause disease even though the silent copy is intact, which makes the parent of origin medically important.

Imprinted genes are relatively few and often cluster together, sharing control regions. Many influence growth and development, fitting the idea that imprinting reflects an evolutionary balance over how much a parent invests in each offspring.