Two Mutators and Their Suppressors in DROSOPHILA ANANASSAE.

Assays of seven mutant stocks exposed a ten-fold range in spontaneous Minute mutation frequencies. Genetic analysis of the difference between the px (0.0006 Minutes) and bri (0.0042 Minutes) stocks revealed that each of these stocks lacks one of two complementary, autosomally transmitted, maternally expressed, dominant suppressors of a dominant 3-linked mutator present in the bri stock. Analysis of the ca; stw stock (0.0013 Minutes) with respect to the former two indicated the presence of the autosomal suppressor functions in addition to a maternally expressed, extrachromosomally transmitted, suppressor of a paternal chromosome-breaking mutator, which is also extra-chromosomally transmitted. The lesions induced by the two mutators in male carriers are probably different, but both kinds are subject to modification by the maternal suppressors soon after fertilization. The existence of these diverse controls of mutability is viewed as confirmation of Sturtevant's (1937) argument that natural selection invokes a variety of devices to minimize mutation rates while retaining mutational potential.