Peromyscus

Peromyscus is a genus of primarily New World rodents, including animals commonly called deer mice. It is distinct from the genus of the house mouse and has become useful for studying variation in ecology, behaviour and reproduction among related species.

Crosses between two Peromyscus species produced growth differences depending on which species supplied the mother and father. Analysis found disruption of genomic imprinting in the hybrids, while imprinting remained present in the tested parental species. ^[ref] The result distinguishes a hybrid regulatory mismatch from complete absence of the mechanism in one parent. Swapping the direction of a cross can expose parent-of-origin effects hidden by a single pooled hybrid category.