Functional identification of the Segregation distorter locus of Drosophila melanogaster by germline transformation.

Segregation Distorter (SD) is a meiotic drive system in D. melanogaster that results in the failure of SD/SD+ males to transmit SD+ homologs owing to the induced dysfunction of spermatids carrying the normal chromosome. Segregation distorter (Sd), the gene primarily responsible for this distorted transmission, is associated with a novel 12-kb restriction fragment containing a tandem duplication of a 5-kb wild-type segment of genomic DNA. When introduced into appropriate genetic backgrounds by germline transformation, this 12-kb fragment causes full levels of distortion and directs the expression of an SD-specific 4-kb transcript. Transformants that have lost part of this segment are unable to cause distortion and do not express the 4-kb transcript. These results identify the tandem duplication as Sd.

The mouse t complex distorter-3 (Tcd-3) locus and transmission ratio distortion

SummaryA novel central partial t haplotype was generated by screening for a recombination event between overlapping distal and proximal partial haplotypes. This haplotype contains just two elements Tcrt and Tcd-3t —involved in the t-specific transmission ratio distortion phenotype. Breeding analysis of males that carry this chromosome provides evidence that Tcd-3 is, indeed, a distorter locus and not a second responder. Furthermore, the data indicate that a single well-defined distorter locus is insufficient to overcome completely the self-destructive, low transmission ratio distortion phenotype expressed by the t allele at the t complex responder locus, although a small, but highly significant, effect was observed.

Five of the nine genetically defined regions of mouse t haplotypes are involved in transmission ratio distortion

SummaryMouse t haplotypes have been divided into nine subregions that are each defined by one or more molecular markers. In previous studies, three of these subregions were shown to contain ‘distorter loci’ that interact to effect the transmission-ratio distortion phenotype characteristic of all complete t haplotypes. To determine which of the remaining six subregions also play a role in this phenotype, we analysed the accumulated data on transmission ratio distortion from males that carried one of 26 different combinations of two partial t haplotypes. We have obtained evidence for the association of two additional subregions with distorter loci. First, we present further evidence for the existence of a previously postulated distorter locus, Tcd-3, and describe its mapping to the T66C subregion. Secondly, we describe the identification of a new distorter locus, Tcd-4, in association with the subregion defined by the structural gene for the TCP-1 protein. Further studies indicate that two doses of the Tcd-4 locus are equivalent in effect to a single dose each of Tcd-4 and a second distorter locus, Tcd-1. This result suggests that different distorter locus products could have a common mode of action.