Mass Selection for Post-weaning Growth in Mice.

EASUREMENT of population change resulting from selection has been one of the useful approaches in the study of quantitative inheritance (see, for example, MATHER and HARRISON 1949; MACARTHUR 1949; LERNER and DEMPSTER 1951; BELL, MOORE and WARREN 1955; FALCONER 1955; ROBERTSON 1955; CLAYTON, MORRIS, and ROBERTSON 1957; MARTIN and BELL 1960; FRASER and KINDRED 1960; THODAY and BOAM 1960; WOLFE 1961 ; and LENG 1962). Moreover, it is quite clear that there is more to be learned from good selection experiments. For general discussions of selection studies, see LERNER (1958) and FALCONER ( 1960). The data to be reported in this paper were obtained in a study initiated in 1957. The most recent data included were collected in October, 1962, and reflect selection practiced during 17 successive generations. From the outset, long-term objectives have been: (1) To determine with all reasonable assurance, the maximum increase in average post-weaning growth that could be achieved by recurrent mass selection in the population to be described, and (2) To identify the cause (or causes) for ultimate cessation of response. Most specifically, the object in this connection is to provide unambiguous evidence for overdominance if there is any. This will be attempted through analysis of consequences of selection for combining ability with one or both of the foundation inbred lines. Such selection is to be initiated when it appears that response to mass selection has ceased. The critical phase of the experiment with respect to these objectives has not been reached. This paper deals with effects of selection (through 17 generations) and various related issues. It should be noted that the experiment being discussed provided the information reported by RAHNEFELD, BOYLAN and COMSTOCK (1962).