THE GENETICS OF THE DORSAL-BICAUDAL-D REGION OF DROSOPHILA MELANOGASTER

The chromosomal region 36C on 2L contains two maternal-effect loci, dorsal (dl) and Bicaudal-D (Bic-D), which are involved in establishing polarity of the Drosophila embryo along the dorsal-ventral and anterior-posterior axes, respectively. To analyze the region genetically, we isolated X-ray-induced dorsal alleles, which we recognized by virtue of the haplo-insufficient temperature-sensitive dorsal-dominant phenotype in progeny of single females heterozygous for a mutagenized chromosome. From the 20,000 chromosomes tested, we isolated three deficiencies, two inversions with breakpoint in dl and one apparent dl point mutant. One of the deficiencies, Df(2L)H20 (36A6,7; 36F1,2) was used to screen for EMS-induced lethal- and maternal-effect mutants mapping in the vicinity of dl and Bic-D. We isolated 44 lethal mutations defining 11 complementation groups. We also recovered as maternal-effect mutations four dl alleles, as well as six alleles of quail and one allele of kelch, two previously identified maternal-effect genes. Through complementation tests with various viable mutants and deficiencies in the region, a total of 18 loci were identified in an interval of about 30 cytologically visible bands. The region was subdivided into seven subregions by deficiency breakpoints. One lethal complementation group as well as the two maternal loci, Bic-D and quail, are located in the same deficiency interval as is dl.