IN sexually dimorphic animals, the determination of sex is a major branch point in development. Although mutations producing sex reversal shed some light on the processes by which this determination is reached, many questions remain unanswered. Autosomal mutations such as polled in the goat1, sex reversed (Sxr)2 in the mouse and transformer (tra)3,7 in Drosophila cause chromosomal females to become phenotypic males, although they are sterile and their gonads agametic. The nature of this sterility suggests that the sex of germ cells in Drosophila, and perhaps in other species, might be determined by different sets of genes from those which operate in somatic tissue. Here we test this hypothesis by constructing mosaics in Drosophila where germ cells of one genotype are surrounded by soma of another. We find that the transformer mutation affects only the somatic sexual differentiation, and that it has no effect on the differentiation of germ cells. Thus we conclude that the agametic nature of transformed flies is due to the absence of functional male germ cells and at least with respect to tra, germ line and soma have separate sex-determining genes.
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