Abstract
Morgan and Bridges (1919, Carnegie Inst. Wash. publ. 278) have recently described and discussed a large number of gynandromorphs of Drosophila melanogaster. They conclude that all female parts in gynandromorphs of this animal contain two X-chromosomes, and that all male parts contain only one X. The peculiarities of a given part are thus due to its own constitution, and are not dependent on the rest of the body for their differentiation. The same principle was found to hold for the characters determined by the sex-linked genes, which are carried by the X-chromosomes.
I have recently obtained evidence indicating that the sex-linked character vermilion forms an exception to this rule. A gynandromorph was obtained in which the male parts showed the sex-linked characters scute, echinus, cut, garnet, and forked. These male parts included the whole head, in which region effects of all five of these sex-linked genes could be identified with certainty. Only one of these genes was present in the mother of the gynandromorph, which was heterozygous for the sex-linked genes eosin, ruby, forked, “vermilion lethal,” and perhaps for vermilion. All five of them were known to be present in the single X of the father of the gynandromorph, which must therefore have been the X present in the male parts of the gynandromorph itself. But the X of the father was known to carry also the gene for vermilion, and the eyes of the gynandromorph were not vermilion. The not-vermilion color was, then, apparently determined not by the genetic constitution of the eye-pigment itself, but by that of some other portion of the body.
I have obtained two other gynandromorphs in which vermilion seems to have reacted in the same fashion; but these are not so certain as the case described.
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