Narrowing the critical regions for mouse t complex transmission ratio distortion factors by use of deletions

Previously a deletion in mouse chromosome 17, T-22H, was shown to behave li ke a t allele of the t complex distorter gene Tcd1, and this was attributed to deletion of this locus. Seven further deletions are studied here, with the aim of narrowing the critical region in which Tcd1 must lie. One deleti on, T-90H, together with three others, T-31H, T-33H , and T-36H, which exte nded more proximally, caused male sterility when heterozygous with a comple te t haplotype and also enhanced transmission ratio of the partial t haplot ype t(6), and this was attributed to deletion of die Tcd1 locus. The deleti ons T-29H, T-32H and T-34H that extended less proximally than T-30H permitt ed male fertility when opposite a complete t haplotype. These results enabl ed narrowing of the critical interval for Tcd1 to between the markers D17Mi t164 and D17Leh48. In addition, T-29H and T-32H enhanced the transmission r atio of t(5), but significantly less so than T-30H. T-34H had no effect on transmission ratio. These results could be explained by a nerv distorter lo cated between the breakpoints of T-29H and T-34H (between T and D17Leh66E). It is suggested that the original distorter Tcd1 in fact consists of two l oci: Tcd1a, lying between D17Mit164 and D17Leh48, and Tcd1b, lying between T and D17Leh66E.