Male crossing-over and location of the male determining factor on the third chromosome in a III^M-type strain of the housefly

Abstract

A dominant wing-shape mutation, Bx² (Beadex²), occurring on the III^M-chromosome was found in a wild-type housefly strain named Nagai. By backcrossing hybrid males between the Bx² male and the third chromosomal mutant bwb ge females to the homozygous recessive mutant females, a new type of sex-limited strain designated as "bwb ge/Bx² M(Nagai)" was established. The strain usually kept producing only male progeny with Bx² phenotype and the female progeny with bwb ge phenotype, but the recombinant type offspring also segregated although the frequency was very low. Further analyses of these recombinants indicated that some of them were the resultants of crossing-over in the male parents, but the others were not. By using the male crossing-over data, the location of the male determining factor on the third chromosome was estimated to be the right side of ge locus.