HETEROSIS AND COMBINING AND MATERNAL ABILITIES IN MOUSE LITTER WEIGHT

Abstract

Four inbred strains of mice (C3H/He, CBA/J, C57BL/6J and SWR/J) were mated in all possible combinations to produce inbred and F1hybrid litters contemporaneously. Each litter was divided into two groups by sex. The total weight of individuals in each group (group weight) and the number of individuals within group (group size) were recorded at birth and at 12, 25 and 45 days of age. The average weight of individuals within a group was calculated for each group. Least squares analyses of group weight, group size, and average weight were performed. The sexes differed significantly in group weight only at 25 and 45 days. The four inbred strains did not differ significantly in group weight at any age. Group weight was greater in F2hybrids than in inbreds at the four ages. Heterosis in group weight was mainly due to heterosis in average weight. Neither the general and specific combining ability effects nor the residual reciprocal effects were significant in group weight. Maternal effects on group weight differed significantly among the four strains at 12, 25 and 45 days. These differences in maternal effects were mainly due to the differences in maternal effects on group size. When group weight was adjusted for group size, a shift in ranking of strains was observed in the inbred strain and maternal effects.