Spontaneous mutations and mutation rates in the house mouse.

HE frequency of occurrence of spontaneous mutations has been under investigation in the extensive mouse breeding colonies of the Jackson Laboratory since the autumn of 1963. The primary goal of this study is to estimate the spontaneous mutation rates, both forward and reverse, at each of five specific coat-color loci (non-agouti, a, brown, b, albino, c, dilute, d, and leaden, In). A secondary goal is to estimate an overall rate using all of the mutations found. Forward natural mutation rates based on large numbers of mice have been reported by RUSSELL (1963) and by CARTER, LYON, and PHILLIPS (1958). Preliminary estimates of rates in this study have been reported by GREEN, SCHLAGER and DICKIE (1965, 800,000 mice examined) and by SCHLAGER and DICKIE (1966, 1.5 million mice examined). This report will present estimates based on 3.5 million mice examined, representing ten million gene reproductions at the five specific coat-color loci, and 1.3 to 6.9 million gene reproductions at each of 40 other loci. These data were collected during the period from August 1963, through April, 1966. and include the data previously reported.