The Frequency of X-ray Induced Dominant Mutations Affecting the Skeleton of Mice.

ADIATION induced dominant effects on viability in mammals are statistically demonstrable (HERTWIG 1938; RUSSELL 1957; RUSSELL and RUSSELL 1958; Cox and WILLHAM 1962). RUSSELL and RUSSELL 1959) emphasized that these effects may well prove to add up to a greater damage in the population than the lethal effects of mutations in homozygous condition. However, very little is known about the rate at which dominant visible mutations are induced by radiation in mammals. Studies by SNELL (1935), CHARLES (1950) and CHARLES, TIHEN, OTIS and GROBMAN (1960) yielded some information about the frequency of X-ray induced dominant visible mutations in mice, including those detected only by autopsy. Additional information was obtained as a by-product of mutation rate studies of seven selected loci (RUSSELL 1951; CARTER, LYON and PHILLIPS 1958,1960). For the evaluation of the hazard of irradiation to a population, it is desirable to obtain more information about the frequency of induced dominant visible mutations. This was one of the reasons why an experiment was designed to test the feasibility of measuring part of the overall genetic damage by means of skeletal studies in the F, generation (EHLING and RANDOLPH 1961). The skeleton was chosen because it is formed over an extended period of development and is: therefore, presumably subject to modification by gene action falling within a wide range of time. It was demonstrated that it is possible to distinguish between the effects of newly occurring dominant genetic changes and variability from environmental causes ( EHLING and RANDOLPH 1962). The present experiment is an extension of the earlier one, and was designed primarily to obtain a more reliable estimate of the frequency of X-ray induced presumed dominant mutations affecting the skeleton of mice. The progeny was selected to sample gametes irradiated in postspermatogonial stages. A preliminary report of some of the results has been published (EHLING 1964).