Genetic instability in Drosophila melanogaster: De novo induction of putative insertion mutations

The capacity of a so-called male recombination (MR) chromosome in Drosophila melanogaster to generate mutations at 14 X-chromosome loci specifying visible phenotypes was investigated. Appreciable increases in mutation were found at three loci y, sn, and ras. Tests of represnetative mutants generated at each locus establish all to be putative insertion mutants, as judged by their spontaneous mutability. These facts suggest that insertion mutation production may be a general function of MR chromosomes. The relationship of the MR chromosomes to established insertion elements (IS and Mu) is discussed.