An Investigation of the Genetics of "Male Sex-Ratio" Phenotype in DROSOPHILA PSEUDOOBSCURA.

A laboratory strain of Drosophila pseudoobscura (L116) is studied that, when crossed to sex-ratio homozygous females, produces sons that exhibit varying levels of the male sex-ratio (msr) phenotype. The msr phenotype occurs only in sex-ratio males and is due to the production of a high frequency of nullo-XY sperm. The level of the msr phenotype is variable, and new variability is generated in one father-son transmission. Pedigree studies indicate the genes for msr reside on the Y chromosome or the autosomes of the L116 stock.