Placentophagia in nonpregnant nulliparous mice: a genetic investigation.

The genetic influence on the response of nonpregnant nulliparous mice to foster placenta was investigated. Two highly inbred strains (BALBI cBy and C57BL/6By), their F 1 hybrids, a backcross generation, and seven recombinant-inbred strains derived from the F2 generation were tested. It was concluded that there is a genetic component to the response of female. mice to placenta in the absence of previous experience, and that more than one, but possibly as few as two loci are involved. Alternative explanations of average dominance for placentophagia and for no placentophagia (by the promotion of competing responses) were considered.