A search for transmission ratio distortions in offspring from crosses between inbred mice.

Equal transmission of the two alleles at a locus from a heterozygote parent to the offspring is rarely violated. Beside the differential embryonic mortality, nondisjunction and gene conversion that are rather irregular forms of transmission-ratio distortion (TRD), there are two major forms of departure from Mendelian segregation. The first, found in females, based on the asymmetric nature of female meiosis, is usually referred to as meiotic drive, and has been well documented in a few cases. The second is segregation distortion found in males. There are several known male-related segregation distortion systems that are caused by different fertilizing capacity of sperm cells carrying alternative alleles at a particular locus. Observation of TRD effects requires a sufficient number of offspring produced by a parental pair. As individuals in a population most likely have different genotypes in TRD affecting loci, the total transmission ratio is close to the expected Mendelian ratio and masks potential TRD effects. Highly inbred strains of laboratory mice provide a very good model for studying this phenomenon, because comparing two mice strains is effectively similar as comparison of two individuals in a population. This study tests both forms of TRD in progeny of F1 hybrids from reciprocal crosses of inbred mice. Three previously unknown instances of TRD in females were observed. Therefore, this study concludes that some genes in females may carry alleles that can cause segregation distortion.