X-ray-induced specific-locus mutation rate in newborn male mice

The specific-locus mutation frequency resulting from 300 R of acute X-irradiation has been determined for the germ cells present in newborn male mice. The frequency is 13.7·10^?8 mutations/locus/R, which is statistically significantly lower than that of 29.1·10^?8 mutations/locus/R found earlier for the same loci in spermatogonia of the adult male by W. L. Russell. The mutation rate for newborn males does not differ significantly from the induced specific-locus frequency reported for fetal males by T. C. Carteret al.The incidence of clusters of specific-locus mutations found following the irradiation of the newborn males was statistically significantly higher than the cluster incidence reported by W. L. Russell for similar irradiation of adult males. This presumably indicates the survival of relatively fewer reproductive cells following irradiation of the day-o testis.Although there are suggestions that the distribution of mutations among the loci following irradiation of the newborn males may be different from that of the irradiated adults, no statistically significant differences are demonstrated.It is quite possible that the testis of the newborn mouse may be comparable to the relatively undifferentiated human testis which persists for approx. 10 years. Until the present research was undertaken, no attempt had been made to determine the specific-locus mutation frequency resulting from X-irradiation of newborn male mice. Although some important questions still remain concerning the explanation for the lower mutational response of the newborn mouse testis, from the hazard standpoint it is reassuring that the mutation frequency of the newborn male is statistically significantly lower than that of the adult.