Cytogenetic Analysis of Chromosome 3 in Drosophila Melanogaster: Mapping of the Proximal Portion

In order to define more precisely the most proximal portion of chromosome 3R in Drosophila melanogaster, several new chromosome aberrations involving this region have been recovered and analyzed. These new arrangements were recovered as induced reversions of two dominant mutations, AntpNs and dszD, located in the region of interest. The results of the analysis have allowed the localization of several existing mutations, have further elucidated the complex homoeotic locus which resides in this region, and have confirmed the efficacy of this type of screen in the analysis of specific chromosome regions. proximal portion of 3L from st to the centromere has been rather well T%rated with chromosome aberrations by LINDSLEY et al. (1972) and further information is not really needed. However, the proximal region of 3R is not saturated to the same extent. Two small deficiencies in the most proximal portion of 3R (81F-82A and 82B-C) can be synthesized using the Y-3 translocation stocks of LINDSLEY et al. (1972). However, in the region from 82C to 8SE, it is possible to make only one deficiency (83E,F-84D). Since this segment (proximal 3R) is the most likely locale of a large group of ts lethals (TASAKA and SUZUKI 1973), as well as a complex homoeotic locus ( DENELL 1973), we set out to create several new chromosome aberrations in this area of the third chromosome. The results of LINDSLEY et al. (1972) demonstrate that, except for the Minutes, most dominant mutations are located in regions which result in a normal phenotype when haploid, since their dominant phenotypes are not expressed in Deficiency/+ heterozygotes. They point out that it should be possible to revert such dominants by deleting them. Therefore, the method chosen to screen for chromosome aberrations in proximal 3 R was to search for radiation-induced loss of the phenotypes expressed by two dominant mutations known to be located near the centromere of the third chromosome. They are Nasobemia (AntpN8) and doublesex-Dominant ( dszD) . This report concerns the recovery and characterization of several newly induced revertants of these two mutations. ’ Supprted by National Research Council of Canada grant A-1764 and the National Cancer Institute of Canada a Present address: Department of Genetics, University of Washington, Seattle, Washington. contract 6051 to DAVZO T.SUZUHI. Genetics 80 I 732-752 August, 1975. 734 I. W. DUNCAN AND T. C . KAUFMAN MATERIALS A N D METHODS All flies were raised on standard dried yeast, cornmeal and dextrose medium and all r o u b e work was carried out at 22" +I". Larvae destined for salivary gland chromosome preparations were raised at 17" 2 1". All irradiations were done by packing 50-100 adult males of varying ages into gelatine capsules and administering approximately 4000r of gamma radiation from a cobalt-60 Gammacell. Detailed descriptions of the properties of the mutations and chromosome aberrations used can be found in LINDSLEY and GRELL (1968); those of special interest to this study are listed with a brief description in Table 1.