SPONTANEOUS UNEQUAL EXCHANGE IN THE ROSY REGION OF DROSOPHILA MELANOGASTER

William M. Gelbart ¹ and Arthur Chovnick ²

¹ Cellular and Developmental Biology, Harvard University, 16 Divinity Avenue, Cambridge, Massachusetts 02138
² Genetics and Cell Biology Section, Biological Sciences Group, The University of Connecticut, Storrs, Connecticut 06268

A selective system for recovery of exchanges between trans mutations at adjacent loci, l(3)S12 and rosy, is described. In addition to the expected cross-over and conversion classes, two exceptional types of offspring were recovered. Triploid offspring arose as 0.01% of all zygotes; the diploid chromosome set was apparently of maternal origin. Nine tandem duplications derived from unequal exchange between nonsister homologues were recovered among 2.25 x 10⁶ zygotes screened. From considerations of the proportion of the genome that was assayed in this system, and on the assumption that the rate of unequal exchange observed is typical for the genome as a whole, it appears that one unequal exchange occurs per 500 female meioses in Drosophila.