Evidence for Two Regions in the Mouse t Complex Controlling Transmission Ratios

Four new t haplotypes, t^Tu1 through t^Tu4, are described, three of them derived from the t^w12tf haplotype and one (t^Tu4) from the t^w2 haplotype. The t^Tu1 and t^Tu4 haplotypes cause taillessness in T/t^Tu1 or T/t^Tu4 heterozygotes, lack the lethality factor, weakly suppress recombination in the T−H−2 interval, and are transmitted to offspring from t^Tu/ + males at nearly Mendelian ratios. The t^Tu3 haplotype resembles t^Tu1 and t^Tu4 except for the fact that the T/t^Tu3 heterozygotes have normal-length tails. The t^Tu2 haplotype probably carries the lethal factor of t^Tu12tf, suppresses crossing-over in the T-H-2 and tf-H-2 intervals, and displays a slightly subnormal transmission ratio. In the compound heterozygote t^Tu1/t^Tu2, the male transmission ratio of the t^Tu1 chromosome is close to that of the original t^Tu12tf haplotype. A similar effect is observed in the t^Tu3/t^Tu2 heterozygote. This observation is interpreted as evidence for two regions within the t complex controlling the male transmission ratios. One of the regions is close to the tail-modifying region, the other is close to the lethality factor. Our findings parallel closely those made in the segregation distorter system in Drosophila.