Difference between two hybrid stocks of mice in the incidence of congenital abnormalities following X-ray exposure of stem-cell spermatogonia

Female mice were exposed to varying absorbed doses (108-504 rad) of X-rays and mated at different intervals after irradiation (1-7, 8-14, 15-21 and 22-28 days). Uterine contents were examined at late pregnancy in order to detect early fetal deaths (dominant lethality) and malformations in the live fetuses. Two trends were apparent from data on abnormal fetuses. At each weekly interval, the incidence of abnormalities tended to rise with increase in dose, and, at any given dose, the incidence tended to increase with time after irradiation. Dwarfism and exencephaly were the two most common malformations found. The changes in incidence of dominant lethality and of abnormal fetuses with time and with dose follow each other closely, the highest incidence for both being reached in week 3 (59 +/- 4.7% for dominant lethals and 12.5 +/- 3.1% for abnormal fetuses, after 504 rad) indicating increased radiosensitivity of less mature oocytes. These results parallel those obtained from known genetic effects reported by other workers and suggest that testing for incidence of congenital malformations among offspring of treated animals may prove a useful means of assessing genetic hazards of radiation or chemicals.