Studies of the genetic variability in populations of wild house mice .2. Analysis of eight additional alleles at locus – T

1 Eight additional lethal alleles at locus T are described, each derived from a wild heterozygote in one of six different wild populations.
2. The frequency of heterozygotes appears to be high in most wild populations, possibly as high as 50 percent.
3. In two of the populations in which several heterozygotes were found, the same allele was isolated from each heterozygote of the same population. One heterozygote was found in each of two subpopulations on the same farm. These two alleles have not been shown to be different. One wild heterozygote from another population transmitted two different alleles; probably one was a new mutant, giving rise to the possibility that more than one allele may occur in the same population, although the rule at present is to find but one type of variant allele per population.
4. All wild t alleles show the “male segregation ratio peculiarity” by which male heterozygotes transmit the t allele to a great majority (about 96 percent) of the offspring. This may be due to the effects of natural selection on factors favoring high transmission ratios.
5. t alleles from the wild fall into at least three groups, one with three viable alleles,
and two groups of lethals. Lethals within the same group have not formed viable compounds when combined; lethals belonging to different groups do form viable compounds by complementary interaction and are thus shown to be nonidentical.
6. Since 29 alleles have now been detected at this locus, many of which are nonidentical, the locus is assumed to contain many sites of mutation and to have great potential complexity.