Impact of interpopulation distance on dominance variance and average heterosis in hybrid populations within species.

The article investigates how genetic distance between populations within a species affects dominance variance and average heterosis in hybrid crosses, focusing on populations typical in crop and livestock breeding. It presents analytical expressions relating Nei's minimum genetic distance and the correlation of allele frequencies between two populations to (1) the variance of dominance deviations (a component of specific combining ability, SCA) and (2) the expected average heterosis in their hybrids. The study finds that dominance variance decreases with increasing genetic distance up to the point where allele frequencies become uncorrelated, then increases if frequencies are negatively correlated, while average heterosis consistently increases linearly with genetic distance. These results clarify that, for populations not too genetically distant and under similar selection pressures, greater divergence generally enhances heterosis and improves the efficiency of hybrid selection, complementing and extending previous theoretical and empirical findings in plant and animal breeding.