Abstract
Frequencies of sex chromosome aneuploid sperm were measured for standard and "sex-ratio" Drosophila pseudoobscura males with identical genetic backgrounds. The "sex-ratio" males produced a 15.6-fold higher frequency of nullo-XY sperm than the standard males produced, but diplo-XY sperm were produced at the same rate in the two types of males. "Sex-ratio" males with the same SR chromosome but with different chromosome backgrounds were found to produce different frequencies of sterile sons. These results indicate that strains of D. pseudoobscura differ at autosomal or Y-linked modifiers of sr. Such modifiers are similar to the msr genes found in the L116 strain of this species.
