Transmission ratio distortion in mice

The most studied example of transmission ratio distortion (TRD) in mice is that of the t-complex. This is a variant-region of Chromosome 17 which exists as a polymorphism in wild mice. Males heterozygous for a t-haplotype and a normal Chr 17 transmit-the t haplotype to >50% of their young, up to 99%.- Homozygous males are-sterile. The TRD produced by-the t-complex, is due to the action of three or more distorter genes (Tcd) on a responder. gene (Tcr). t-Haplotypes are maintained intact by crossover suppression induced by four neighboring inversions, the Tcd and by Tcr loci lying in different inversions. Sperm formation is normal in t/t males, but sperm function is impaired through gross defects in sperm motility. The responder gene has been identified as a fusion gene formed from a sperm motility kinase and a ribosomal S6 kinase. Three candidate distorter genes have also been identified as genes coding for dynein chains, and thus possibly involved in sperm flagellar function.