Low-Dose X-Ray Effects on the Precleavage Mammalian Zygote

By limiting the mating time of CF1 and CF1-S mice to a period of 40 to 45 minutes, zygotes could be exposed to x-ray doses of 10, 15, 25, and 50 R at various ages. Sixty groups of 50 mice each were x-irradiated at different times from 1 to 12 hours, 18, 24, and 30 hours after insemination, at each of the dose levels, to determine the effect of these low doses on the preimplantation stages of the zygote. A total of 34,804 x-irradiated and 9950 control implantations were examined at the eighteenth day of gestation and classified as resorbed, dead, anomalous, or apparently normal. There was a statistically significant reduction in the number of implantations when 50 R was applied to the 6- to 8-hour-old zygotes. There was a reduction in implantations for the same age group x-irradiated at 25 R. The percentage of apparently normal live fetuses among the implantations at the eighteenth day of gestation was used as the basic variable. There was a significant decrease in the percentage of normal implantations at...