On the Nature of Size Factors in Mice

Abstract

Data on quantitative characters, derived from a mouse species cross, have shown that the F1 means fall into two general classes: one in which the means are intermediate between those of the two parent species and the other in which they equal or surpass the larger parent. In general, external dimensions (body length, tail length) and weight fall into the first; while skeletal dimensions fall into the second. Humerus length, however, is intermediate. These results make it appear probable that not all size characters are equally subject to the influence of general factors. Coefficients of correlation were computed for various pairs of characters and disclosed significant differences. Femur and tibia are more closely correlated than is either with skull length. These two leg bones in mice, as well as in rabbits, are apparently largely influenced by common factors. Sex differences were found in the degree of correlation between various pairs. In general, females present higher coefficients than males perhaps indicating that general size factors play a more important role in the former.