Morphometric studies in inbred and hybrid house mice. II. Patterns in the variances.

Genetic and environmental components of variation were estimated for 15 osteometric and 3 external metric traits from nested analyses of variance in inbred and hybrid male and female house mice. In inbred males and females, respectively, the average contribution over all 18 characters for the within-litter variances was 26.4 percent and 15.3 percent; for the between-litter variances, 9.3 percent and 7.2 percent; and for the among-strains variances, 64.3 percent and 77.5 percent. For the combined sexes, the average genetic contribution (broad sense heritability) for the morphometric characters was 71 percent, and the coefficient of genetic determination, 57 percent. In hybrid males and females, respectively, the average contribution of the within-litter variances was 20.1 percent and 36.8 percent; for between-litter variances, 10.2 percent and 21.4 percent; for reciprocals variances, 59.3 percent and 28.2 percent; and crosses variances, 10.4 percent and 13.6 percent. Both in relative and absolute terms, the genetic variances for hybrids averaged much less than those for inbreds. All characters except body weight showed significantly less environmental (within plus between-litter) variation in hybrids compared with inbreds. Heterosis did not appear to be associated with the differences in the magnitude of genetic or environmental variation between sexes or breeding types.