Ethyl methanesulfonate-induced mutations of major genes for quantitative phenotypes: mutant alleles for altered activity of brain or liver enzymes in C57BL/6J mice and their inheritance across several generations.

We recently identified and confirmed 8 induced mutations in the N2 and N3 progeny of ethyl methanesulfonate (EMS) treated C57BL/6J mice. Each of these mutations altered specific enzyme activities. These separate mutant sublines have been maintained through several generations as heterozygous mutant carriers. The percent decrease of the specific enzyme activity from normal in each subline was calculated for each generation. Additionally, the percentage of breeders within each mutant subline producing abnormal progeny and the fraction of such breeders' total progeny possessing abnormal activity were determined. The aberrant activity values observed in progeny of a confirmed mutant carrier were all lower than normal. 4 of the mutant sublines had decreases in enzyme activities which were constant across the generations analyzed. 3 of the mutant sublines had decreases in activities which were consistent over early generations but changed significantly in later generations. Another subline with decreased enzyme activity was lost. For 7 of the sublines, the number of progeny having altered activity and the number of breeders producing mutant progeny approximated that expected for single gene inheritance. In the remaining subline, a change in the decrease in enzyme activity probably accounts for the deviation from expected inheritance. Although the phenotypes for these quantitative traits are considered to be quasi-continuous, the data indicate that the mutations are probably of major genes.