Genetics of Body Size and Related Characters. II. Satellite Characters Associated with Body Size in Mice

Abstract

In the previous paper, the author had described the formation of a large and a small race of mouse by selection from a common stock. The small race was active, agile, and "wild"; the large race tended towards sluggishness and obesity. Differences in coat colors between the 2 races resulted from pleiotropic effects on size of coat color factors. Short ear, a factor with a pleiotropic growth-retarding effect, was segregating in litters of the large race, probably due to linkage to dilute, a coat color factor also accelerating growth. Appendages, such as tails, ears, and feet, were relatively longer in the small race. The growth rate of appendages slowed down sooner than that of the body, and body growth stopped sooner in the small than in the large race. The large race had litters of 3 to 15 young in contrast to only 3 to 8 young in litters of the small race. This correlation between body size and litter size was probably to be traced to the hormones of the anterior pituitary which had aggrandizing effects on both characters. In addition, the young of the large race were individually heavier. The relationships among pleiotropic effects and physiol. correlations resulting from selection for one leading character seemed to support Darwin''s idea that selection produces correlated rather than independent changes. The application of these findings to general biol. problems was discussed.