Specific locus mutation rates after repeated small radiation doses to mouse oocytes

When female mice were given a dose of 20 × 10 rad X-rays, the specific locus mutation rate among offspring conceived up to 7 weeks after the end of treatment was 1/39887 or 0.18·10⁻⁷/rad/locus, whereas when the same total dose of 200 rad was given in a single exposure the mutation rate was 9/34813 or 1.85·10¹⁰⁻⁷/rad/locus. The lower mutation rate after the 20 × 10 rad dose was obtained whether the total of 200 rad was given over a period of 5 days or 4 weeks, and if only young conceived in the first 20 days, rather than 7 weeks, were considered. It is suggested that each 10 rad fraction had the same small effect, and hence that these results confirm and extend Russell's previous finding that the dose-response relationship for specific locus mutations in females is curved.