Significance of specific-locus germ-cell mutations in mice.

On the basis of a historical-control incidence of 39 mutants in 688 921 progeny (5.7 mutants/10(5) animals or 0.82 mutations/locus/10(5) gametes) proposals are made for the numbers of test progeny required when screening for possible mutagens using the specific-locus test in mice (7 loci). It is recommended that 25,000 control progeny should be included in each test, to establish homogeneity with the historical controls. This would also be the number of progeny required from treated males, unless significantly positive results had been obtained with smaller numbers. It would appear that the greater sensitivity of post-spermatogonial stages could more than compensate for practical difficulties in sampling these stages, rather than spermatogonia, in screening tests.