60 THE ORIGIN OF GYNANDROMORPHS. 



so that each of the two first daughter cells had but one X and these different 

 from each other. 



Zygole. Left side. Right side, 



w m r w m r 



No. I 92. August 16, 1913. C. B. Bridges. Text-figure 49 (diagram). 



Parentage. One of the X chromosomes of the mother carried the genes for 

 vermilion and for fused and the other X the gene for bar. The father was 

 vermilion fused. 



Description. The gynandromorph was completely bilateral, except for 

 the genitalia, which were female. The left side was male, as evidenced by 

 the smaller size throughout, by the sex-comb, and by male coloration on the 

 abdomen. The left eye was bar of the male type. The right side was female 

 in every part, and was chiefly remarkable in that its large wing was fused. 

 The eyes were both red, not vermilion. The right eye was round, not hetero- 

 zygous bar. A pair of ovaries was found in the sections. 



Explanations. On the assumption of two nuclei in the egg, one nucleus after 

 reduction contained a non-cross-over bar X chromosome, and this nucleus 

 fertilized by a Y sperm gave the bar male left side, with bar eye; the other 

 nucleus after crossing-over and reduction contained a cross-over fused X 

 chromosome, wh ch nucleus fertilized by the vermilion fused X sperm gave 

 the female right side with fused wing: 



Left side. Right side. 



B f u 



On the alternative view that both X's from the mother were retained after 

 reduction in the same nucleus of the egg, the case is difficult, but may be 

 accounted for in the following way: Since the left side is male throughout 

 and shows the bar eye-character (of male type), this side must have come from 

 a non-cross-over X of the mother. But this bar X is not represented at all 

 on the right side, as proved by the round eye, which, although female, is 

 not even heterozygous for bar. That the right side is female requires that 

 two X's be present, and the fact that the wing is fused requires that both 

 carry the fused gene. A non-cross-over vermilion fused X must have come 

 from the mother along with the bar X. The egg, then, was an XX egg pro- 

 duced by primary non-disjunction which was equational, since the bar X 

 was a non-cross-over and the fused X a cross-over chromosome (Bridges, 

 1916). This XX egg was fertilized by an X sperm carrying the genes for 

 vermilion and for fused. It is known that XXX zygotes are unable to 

 hatch as adult flies (Bridges, 1916), but since neither the time nor the mechan- 

 ism of their elimination is known, it is possible that if double elimination or 

 somatic reduction followed soon after fertilization the life of the XXX 

 individual would be saved, but at the price of becoming a gynandromorph. 

 Two of the X's, in this case the paternal vermilion fused and the maternal 



