Dose-response relationships for X-ray-induced reciprocal translocations in spermatogonial stem cells of mutant and wild-type mice were established by spermatocyte analysis many cell generations after irradiation. The mutants studied wereWV/+, the viable allele of dominant spotting in the heterozygous state, andSIcon/SIcon, the homozygous contrasted allele of steel. The results show that the recovered yield of translocations was lowered in both mutants with steel being most extreme. Remarkably, however, no indications for enhanced cell killing were obtained in the mutants, and consequently the peak yields of translocations occurred at about the same dose level (6 Gy) as in normal mice. Histological analysis suggested that the postirradiation recovery of the germinal epithelium was retarded in the mutants with the effect in the steel mice again being most extreme. These differences in differentiation-multiplication patterns of regenerating spermatogonia after irradiation are probably responsible for the reduced recovery of translocations from the mutant mice.

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