. Contributions to the genetics of Drosophila melanogaster. Drosophila melanogaster; Heredity; Karyokinesis. 30 THE ORIGIN OF GYNANDROMORPHS. Since there was no white in the stock, the white eye must have come by mutation and possibly by mutation to a sex-Hnked white-eyed gene. (8) In a mating in which both parents were pure bar-eyed flies a male appeared (1917) (text-fig. 12) in which both eyes were round and in addition one eye was three-quarters white, and the other had a fleck of white in it. A germinal mutation in the mother of bar to round eye must have taken place, as shown by the fact
. Contributions to the genetics of Drosophila melanogaster. Drosophila melanogaster; Heredity; Karyokinesis. 30 THE ORIGIN OF GYNANDROMORPHS. Since there was no white in the stock, the white eye must have come by mutation and possibly by mutation to a sex-Hnked white-eyed gene. (8) In a mating in which both parents were pure bar-eyed flies a male appeared (1917) (text-fig. 12) in which both eyes were round and in addition one eye was three-quarters white, and the other had a fleck of white in it. A germinal mutation in the mother of bar to round eye must have taken place, as shown by the fact that when the fly was bred it produced only normal-eyed offspring. Since this male was normal, it must have come from the union of a Y-bearing sperm and an X egg. Since the bar gene is carried by the X chromo- some, it follows here that mutation must have occurred in one sex chromosome of the mother. It is significant in this connection to call attention to the fact that bar-eye not infrequently mutates (reverts) to normal, as May has clearly proven. The other change to white was due to a somatic mutation. (9) In stock pure for black and for miniature and impure for white and for red eyes a male appeared that had one white eye (text-fig. 13). It might appear here that simple elimination in a heterozygous female would account for the white eye, but if the fly arose in this way the rest of it should be female. Double elim- ination will, however, give a result of this kind, i. e., a red X is lost from one half and a white X from Text-figure lo. the other side, leaving both parts male, one red, the other white. If, on the other hand, the fly started as a red-eyed male and dislocation occurred, so that most of the fly had an X, the other part a Y chromosome, the expectation, based on the evidence from nondisjunction, would be that the male part would die. However, it might be claimed that the evidence appHes to the fly as a whole and not to the survival of a small part of the body,
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