Size Inheritance

Abstract

The multiple factor hypothesis is correct in the assumption that many independent genes influence body size, but it is not true that all such gene influences are quantitatively equal or act in one direction only, either plus or minus. Exptl. mouse crosses show that a majority of the common mutant genes have also an influence on body size, some increasing body size, others decreasing it, and still others being neutral. Brown and blue dilutions increase body size and their action is additive. The interaction of brown with leaden and pink-eye2 is peculiar in that the retarding effect of leaden and pink-eye2 on growth, instead of being counteracted by brown, is intensified by it. The mother exerts greater influence than the father on the body size of offspring, as shown by the result of reciprocal crosses between races of unlike body size. The offspring are regularly closer to the mother''s race than to that of the father in size. This is due in part to gestational influences, in part to cytoplasmic constitution of the egg. The action of size genes is chiefly general through control of developmental rate of the embryo, as a whole, but in part through control of the developmental rate of groups of organs, or of single organs independent of general body size, as shown by Wright.