Dominant cataract mutations and specific-locus mutations in mice induced by radiation or ethylnitrosourea

In a combined experiment, dominant cataract mutations and specific-locus mutations were scored in the same offspring. In radiation experiments, a total of 15 dominant cataract and 38 specific-locus mutations was scored in 29396 offspring. In experiments with ethylnitrosourea (ENU), a total of 12 dominant cataracts and 54 specific-locus mutations was observed in 12712 offspring. The control frequency for dominant cataracts was 0 in 9954 offspring and for specific-locus mutations 11 in 169955 offspring. The ratio of radiation-induced recessive visible to dominant mutations was about 2.5:1. The difference was even more pronounced for ENU-induced mutations. The ratio of recessive visibles to dominant cataracts for chemically induced mutations in spermatogonia was about 5.4:1. The two characteristic features of radiation-induced specific-locus mutations--the augmenting effect of dose fractionation and the quantitative differences in the mutation rates between spermatogonial and post-spermatogonial stages--can also be demonstrated for the induction of dominant cataracts. The dominant cataract mutations recovered can be categorized into 7 phenotypic classes: total opacity, nuclear and zonular cataract, nuclear cataract, anterior pyramidal cataract, anterior polar cataract, anterior capsular cataract, and vacuolated lens. The largest class of mutations, a total of 11, affected the anterior polar region, while the number of total opacities in both experiments was 5. The only noteworthy difference observed between the radiation- and ENU-induced mutations recovered was that, of the 2 radiation-induced total lens opacities, both were associated with an iris anomaly and microphthalmia whereas the ENU-induced total opacities were not.