Average Direct and Maternal Genetic Effects and Heterosis Effects on Body Weight in Two Subspecies of Mice

Data on body weights were analyzed in the four genetic groups from all possible crosses of two subspecies of mice to estimate average direct genetic effects (ADGE), average maternal genetic effects (AMGE) and heterotic effect (HE). The genetic groups used were $CF_{{\sharp}1}$ laboratory mouse (Mus musculus domesticus), Yonakuni wild mouse (Yk, Mus musculus molossinus yonakuni) and two reciprocal $F_1$ crosses of them, CY and YC. First symbol in the reciprocal $F_1$ represent subspecies of dam. Body weight at 1 (Wk1), 3 (Wk3), 6 (Wk6) and 10 weeks of age (Wk10) were analyzed from 258 mice of the four genetic groups. The model used to evaluate body weights included main effects of genetic group and sex, and interaction effect between genetic group and sex. The ADGE and the AMGE were estimated as deviations of Yk from $CF_{{\sharp}1}$. The HE was estimated from the differences between the reciprocal $F_1$ and the midparent mean. Results of this study showed that all effects, except sex and interaction between genetic group and sex at Wk1 and Wk3, were highly significant source variation (p < 0.01). The ADGE were positive and highly significant (p < 0.01) at all ages studied for both sexes, while the AMGE were highly significant at Wk3, Wk6 and Wk10. The ADGE were larger in contributing effect on body weight differences than the AMGE. The positive value of the HE were observed at all ages for males, while for females the positive effects occured from birth through weaning.