Cytogenic mapping and isolation of mutations of the beta-Gal-1 locus of Drosophila melanogaster.

The structural gene beta-Gal-1 encoding a beta-galactosidase (EC 3.2.1.23) of Drosophila melanogaster has been mapped by two independent genetic approaches. In the first, gene dosage dependent variation in beta-galactosidase activity levels in segmental aneuploids, generated from crosses of Y-autosome translocation stocks, was determined quantitatively. A dosage sensitive region on the left arm of chromosome 2 was identified and mapped to region 26A7-9. In the second approach, two null activity variants were isolated from wild populations. It was shown by deletion analysis that these nulls map to the same region as that determined by the segmental aneuploidy method. The results of an EMS mutagenesis screen showed that, besides the beta-Gal-1 locus, there are four loci defined by recessive lethal mutations which map in the 26A7-9 region.