Absence of resistance genes against male-killing action of the SRO in Drosophila melanogaster

Males of Drosophila melanogaster bearing various X chromosome segmental aneuploidies were tested for sensitivity/resistance to the male killing action of the Sex Ratio Organism (SRO). It was found that there is no region on the X chromosome which makes, when duplicated, males resistant to the SRO. A region which makes hetero-deficient females sensitive to the SRO also was not found. Searches for a gene (s) that can give males resistance to the SRO action were made using the X chromosomes continuously mutagenized for seven successive generations, the second and third chromosomes obtained from a natural population (100 lines), and the cytoplasm of 100 isofemale lines and twenty-two mass lines from various natural populations. No such genes were recovered. A possible reason for the failure of recovering such a gene is discussed.