Morphometric studies in inbred and hybrid house mice. I. Patterns in the mean values

Fifteen osteometric and three external metric traits were analyzed in mice via a complete set of crosses among three inbred strains (C3HeB/FeHb, C57BL/6Hb, AKR/Hb). Sex was a significant source of variance for 13 traits. All traits showed significant heterosis, and differences among inbreds also were significant for all traits. Crosses were significant for 13 traits, while reciprocal differences were significant for 16 traits. Interactions of sex with heterosis and inbreds were significant mainly for the appendicular and external traits. Interactions of sex with crosses and reciprocals were unimportant. Litter size proved to be a significant covariable for 15 of the 18 variables, whereas "days" was significant for only two variables. Heterosis was positive for all characters except interorbital width, which was negative, the difference between inbreds and hybrids averaging two standard deviations. A significant positive correlation was found between the degree of heterosis for each of the traits and their magnitude of heritability as previously calculated for a randombred population. A multivariate canonical variate analysis also was used, and it correctly classified all but three of the 252 total mice into their appropriate inbred or hybrid class. The first canonical variate, a pelvic-pectoral girdle and limb contrast, clearly separated the two sexes, the second variate (proximal-distal limb contrast) largely contributed to the separation of the inbreds and hybrids, and the remaining variates were generally appendicular bone shape contrasts that separated the inbreds and hybrids in various other ways.