The genetics and cytology of a mutator factor in Drosophila melanogaster

A Drosophila melanogaster mutator factor is described whose effects include the induction of unique chromosomal aberrations and male crossing over. Results of experiments to map the factor suggest that genetic transmission is somehow chromosomally associated but not localizable to the X, Y, second or third chromosome. There appears to be a good correlation between the distributions of male crossover exchange points and unique aberration breakpoints for the second chromosome but not for the third chromosome. The male crossovers, which occur more frequently in the centromeric region, occur in euchromatin rather than in the centric heterochromatin. The male crossovers tend to be rather precise reciprocal exchanges, since cytologically detectable deletions and duplications are only infrequently produced. It is suggested that the present mutator may be identical to earlier reported mutators of D. melanogaster.