Evidence for Multiple Sex Factors in the X-Chromosome of Drosophila Melanogaster

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Abstract
The sex-determining role of the X-chromosome of Drosophila may be accounted for either by assuming the presence of a single sex-determining gene (sex-differentiator) in that chromosome, or by the presence of numerous [female]-determining loci, which taken together transform the [female] into the [male] or vice versa. Data are presented which show that, at least in Drosophila melanogaster, sex is determined by a cooperation of many genes rather than by a single sex-differentiator. Triploid intersexes (possessing 2 X-chro-mosomes and 3 sets of autosomes) exhibit a wide range of forms beginning with [male]-like and ending with [female]-like individuals. The addition to the chromosome-complement of such intersexes of duplications covering various portions of the X-chromosome results in a shift in the type of the intersexes toward femaleness. Data are presented which show that the longer the duplication added, the stronger the shift toward femaleness. The longest of the duplications studied, covering about 4 of the length of the X-chromosome, transforms the intersexes into fertile [female][female]. This is taken to prove that at least all the sections of the X-chromosome involved in the duplications studied contain predominantly 5 sex-determining genes, and that there is no need of assuming the existence of a single sex-differentiator.

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