Preferential survival of mice expressing the Qa-2 antigen.

The Ped gene, a gene that influences the rate of embryonic cleavage division, birth weight, litter size and weaning weight, is at least partially encoded by gene(s) that specify the Qa-2 antigen. Two congenic strains of mice, B6.K1 (Qa-2 negative) and B6.K2 (Qa-2 positive), which differ only at the Q region of the mouse major histocompatibility complex (MHC), were tested for the effect of the presence or absence of Qa-2 antigen on litter size, duration of gestation and embryo survival. It was confirmed that B6.K1 (Qa-2 negative) mice have smaller litters than do B6.K2 (Qa-2 positive) mice. In addition, the duration of gestation for the B6.K1 mice was found to be longer than the duration of gestation for the B6.K2 mice. Finally, a comparison of the relative survival of Qa-2-positive and Qa-2-negative mice in a single uterine environment showed the preferential survival of mice expressing the Qa-2 antigen. Thus, the presence of Qa-2 antigen appears to be advantageous for reproductive success.