Sterile period, translocation and specific locus mutation in the mouse following fractionated x-ray treatments with different fractionation intervals

Adult male mice were given doses of 200 rad acute X-irradiation and mated at intervals to hybrid females over the next 9 weeks. Testis weights fell to 44% of normal during the 5th week and were still subnormal when observations ended in the 10th week. Epididymal-sperm counts fell in the 4th week (after a peak in the 3rd) and were very low in the 6th and 7th weeks, though still above zero. This reduction was followed by high frequencies of pre-implantation loss in females mated to these males and dissected on the 12th day of gestation. Examination of eggs 1–2 days after ovulation showed that there was also a sharp decrease (from the normal level of almost 100%) in the fertilization index, no eggs being fertilized in some females while others showed an intermediate rate. It was concluded that much of the pre-implantation loss really stemmed from non-fertilization rather than from zygotic death. This possibility has already been envisaged by Bateman and others, and reinforces the belief that an index of dominant lethality based on post implantation death should be used whenever the mutagenic treatment is likely to induce much germ-cell killing. The data suggested that reduced fertilization is likely to occur in mice whenever sperm counts fall to less than 10% normal.