Mendelian inheritance of t haplotypes in house mouse ( Mus musculus domesticus) field populations.

Alleles of many genes in the house mouse (Mus musculus domesticus) t complex influence embryonic development, male transmission ratio, male fertility and other traits. Homozygous t lethal alleles cause prenatal lethality, whereas male t semilethal homozygotes and males heterozygous for two complementing t lethal haplotypes are sterile. Without a mechanism maintaining these deleterious genes, t lethals and t semilethals should be eliminated by selection. The mechanism for maintaining them is transmission ratio distortion (TRD), which is said to occur when a t/+ male sires a significantly greater proportion of fetuses carrying his t haplotype (80-100%) than his wild-type chromosome 17. To understand how this selfish DNA functions in trapped populations, the objectives of this study were to examine the structure of t haplotypes in Colorado field populations and to determine transmission ratios in these populations. The data presented here indicate two possible causes for lower than expected transmission ratios in field populations: (1) single-sire fertilization by sperm from mosaic t males may lack all t haplotype genes causing high TRD. (2) t-bearing sperm fertilizing multiple-sire litters are diluted by+sperm from males having the most common genotype (+/+).