Genetic dissection of segregation distortion. I. Suicide combinations of SD genes.

Two major loci in the Tft-cn region of an SD chromosome have been separated by recombination and identified. The allele at the left-hand locus on an SD chromosome is called Sd; the allele at the right-hand locus is called Rsp. Both Sd and Rsp are necessary to bring about a distortion of the segregation ratio in heterozygous SD males, although the particular degree of distortion exhibited by an SD chromosome is influenced by the constellation of polygenic modifiers of SD in the genome. The coupling phase of the alleles, Sd Rsp/Sd(+)Rsp(+), produces about 89-90% of Sd Resp-bearing progeny. The repulsion phase, Sd Rsp(+)/Sd(+)Rsp, produces 10-20% of Sd Rsp(+)-bearing progeny. No coupling-repulsion effects between Sd and Rsp are apparent.