Genetic instability at the cut locus of Drosophila melanogaster induced by the MR-h12 chromosome.

Unstable mutations were generated at the cut locus by the MR-h12 factor which induces male recombination. The unstable allele ctMR2, containing the MR-transposon in the cut locus is a very powerful mutator producing a number of different viable and lethal mutations both in the cut locus and outside it. I describe several types of mutations: stable reversion to wild type, which were sometimes associated with the appearance of unstable mutations in other loci; of stable deficiencies at the cut locus (lethals); new unstable mutations at different loci with the ctMR2 allele conserved; new unstable cut alleles with a phenotype other than that of ctMR2. The possible mechanisms of these mutational events are discussed. The genetic system constructed in the present work affords an opportunity for molecular studies of the cut locus and the MR-transposon, as a sequence from the cut locus has recently been cloned (Tchurikov et al. 1981).