Preliminary characterization of "sex ratio" and rediscovery and reinterpretation of "male sex ratio" in Drosophila affinis.

In D. affinis "sex ratio" (sr), a form of meiotic drive characterized by the production of mostly or only female progeny by certain males, is associated with two different X chromosome sequences, XS-I XL-II and XS-II XL-IV. The behavior of the two sequences differed, depending on the Y chromosome constitution, being either Y(L) or 0. Males with sequence XS-II XL-IV and Y(L) produced progenies with nearly normal sex ratios; males with the same X chromosome sequence but in the absence of a Y chromosome in some cases gave progenies with nearly normal sex ratios but in other cases gave progenies which tended toward phenotypic sr. Males with sequence XS-I XL-II and Y(L) gave progenies which were characteristically sr (0.97-0.98 females); in the absence of a Y chromosome males with this sequence produced progenies which were virtually all-male. This latter finding is presumably identical to Novitski's (1947) "male sex ratio" (msr). The interpretation offered here attributes msr to an interaction between sr sequence XS-I XL-II and the 0 condition. A general consideration of the available data on sr in D. affinis is presented.