Genetic Analysis of the Antennapedia Gene Complex (Ant-C) and Adjacent Chromosomal Regions of DROSOPHILA MELANOGASTER. II. Polytene Chromosome Segments 84A-84B1,2.

The existence of a gene complex in the proximal right arm of chromosome 3 of Drosophila melanogaster involved in the development of the head and thorax was originally suggested by the phenotypes of several dominant homoeotic mutations and their revertants. A screen for mutations utilizing Df(3R) Antp(Ns+R17) (proximally broken in salivary region 84B1,2) yielded, among 102 recovered mutations, 17 localized by deficiency mapping to the putative homoeotic cluster. These fell into four complementation groups, two of which were characterized by homoeotic phenotypes. To explore the limits of the Antennapedia gene complex (ANT-C) more proximally, a second screen has been undertaken utilizing Df(3R)Scr, a deficiency of 84A1-B1,2.-Of 2832 chromosomes screened, 21 bearing alterations localized to polytene interval 84A-84B1,2 have been recovered. Sixteen are recessive lethals, and five showing reduced viability display a visible phenotype in surviving individuals. Complementation and phenotypic analyses revealed four complementation groups proximal to those identified in the previous screen, including two new alleles of the recessive homoeotic mutation, proboscipedia (pb). Ten of the new mutations correspond to complementation groups defined previously in the Df(3R)Antp(Ns+R17) screen four to the EbR11 group, two to the Scr group and four to the Antp group.-On the basis of the phenotypes of the 39 mutations localized to this region, plus their interactions with extant homoeotic mutations, we postulate that there are at least five functional sites comprising the ANT-C. Three have been demonstrated to be homoeotic in nature. The specific homoeotic transformations thus far observed suggest that these loci are critical for normal development of adult labial, maxillary and thoracic structures.