Short Specialist Review Imprinting and behavior

in behavioral phenotypes The crossbreeding of animal species with one another can often produce hybrids with parent-of-origin-specific changes in behavioral phenotypes. For instance, the offspring of a male zebra and a female donkey are noted for their stubbornness in comparison with the reciprocal cross (Gray 1972; Walton & Hammond 1938). For many years, it was unclear why these genetically equivalent individuals behaved in consistently different ways dependent upon parent of origin. Following the discovery of genomic imprinting, it is now acknowledged that these offspring differ in their expression of imprinted genes and that differences in the maternal and paternal alleles of reciprocal crosses at these loci could lead to the observed behavioral differences. Hybrid F1 mice produced from mating a male from an inbred strain A and a female from inbred strain B can be compared with those produced from the recip-rocal cross. If both sets of offspring are transferred as embryos into a different strain C, these offspring are genetically equivalent in every respect with the excep