title: Radiation-induced forward and reverse specific locus mutations and dominant cataract mutations in treated strain BALB/c and DBA/2 male mice.
abstract: Strain BALB/c and DBA/2 mice were chosen to investigate the effects of genetic background on the radiation-induced mutation rate since they exhibit differences in their radiation sensitivity. Males were exposed to 3 + 3-Gy X-irradiation and mated to untreated specific locus Test-stock females. Offspring resulting from treated spermatogonia were screened for induced specific locus forward and reverse mutations and dominant cataract mutations. Since BALB/c mice are homozygous brown and albino, specific locus forward mutations could be screened at 5 of the 7 specific loci (a, d, se, p, s), while reverse mutations could be screened at the b and c loci. Strain DBA/2 is homozygous non-agouti, brown and dilute. Therefore, specific locus forward mutations could be screened at 4 loci (c, se, p, s) and reverse mutations were screened at the a, b and d loci. Results indicate no effect of genetic background on the sensitivity to mutation induction of specific locus forward mutations, while for the dominant cataract alleles strain DBA/2 exhibited a higher mutation rate than either strain BALB/c or similarly treated (101/El X C3H/El)F1 mice. If, by confirmation, these differences should be demonstrated to be real, it is interesting that strain DBA/2 should exhibit a greater sensitivity to radiation-induced dominant mutations. First, strain DBA/2 was chosen as radiation resistant or repair competent. The observation that DBA/2 exhibited a higher sensitivity to radiation-induced mutation may indicate a role for repair, albeit misrepair, in the mutation process. Second, that the effect of genotype was only observed for the mutation rate to dominant cataract alleles may reflect a difference in the spectrum of DNA alterations which result in dominant or recessive alleles. A dominant allele is more likely misinformation, such that as heterozygote it interferes with the wild-type allele. By comparison, a recessive allele may result from any DNA alteration leading to the loss of a functional gene product. One reverse mutation at each of the a and d loci was recovered in the present experiments. The similarities of the present results for radiation-induced reverse mutations with the extensive data on the spontaneous reverse mutation rates are interesting. Reverse mutations were recovered only at the a and d loci. Further, the reverse mutations recovered at the a locus were to alternate alleles (at, Aw or Asy) while true reverse mutations were apparently recovered at the d locus.
mesh_terms: D000016:Abnormalities, Radiation-Induced / Q000235:genetics*; D000483:Alleles; D000818:Animals; D002386:Cataract / Q000209:etiology / Q000235:genetics*; D005260:Female; D005799:Genes, Dominant; D006200:Hair Color; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C / Q000235:genetics*; D008811:Mice, Inbred DBA / Q000235:genetics*; D009154:Mutation; D011836:Radiation Tolerance; D013045:Species Specificity