Genetic Effects of Acute Spermatogonial X-Irradiation of the Laboratory Rat

The genetic effects of one generation of spermatogonial X-irradiation in rats, by a single dose of 600r in one experiment and by a fractionated dose of 450r in another, were measured in three generations of their descendants. Estimates of dominant lethal mutation rates—(2 to 3) x 10 ^-4/gamete/r—from litter size differences between irradiated and nonirradiated stock were consistent with previous estimates from rats and mice. Similar consistency was found for estimates of sex-linked recessive mutation rates—(1 to 2) x 10^-4 chromosome/r—from male proportions within strains; however, when measured in crossbreds the proportion of males was higher in the irradiated than in the nonirradiated lines. This inconsistency in results is in keeping with the contradictory results reported for recessive sex-linked lethal mutation rates in mice. The effects used to estimate recessive lethal mutation rates which were unusually high—(2 to 14) x 10^-4/gamete/r—were not significant. Other factors that could have contributed to the observed effects are postulated.