EFFECTS OF LOW-LEVEL IRRADIATION ON FITNESS AND SKELETAL VARIATION IN AN INBRED MOUSE STRAIN.

the taneous mutations affecting the frequencies of particular variants and becoming incorporated into particular sublines. The rate of subline differentiation is thus a measure of the mutation rate to the genes concerned, which are essentially the same as the “polygenes” of continuous variation. GRUNEBERG therefore suggested that a comparison of the rate of subline differentiation with and without the added factor of irradiation should make it possible to estimate the radiation- induced mutation rate for this type of variation. This is what was attempted in the present experiment.