The frequency of X ray-induced dominant and recessive lethal mutations in the rat.

P A R T of the genetic damage induced by X rays may be due to mutations which have harmful effects on viability. Such mutations may vary in the seventy of their effects from lethal to mildly detrimental, and in degree of dominance from completely dominant or overdominant to completely recessive. The difficulties of obtaining precise mutation rate estimates for viability mutations in mammals are obvious. However, if simplifying assumptions are made, meaningful approximations of the frequency of viability mutations may be made from observations on embryonic survival, on litter size at birth, or on postnatal survival. The present study attempts to estimate the effect of spermatogonial irradiation on the frequency of several classes of lethal mutations in the laboratory rat from data on litter size at birth and postnatal survival.