66 



THE ORIGIN OF GYNANDROMORPHS. 



gene is considered. Normally, the males which possess the lethal 7 gene 

 not only begin development, but continue often to the full-grown larva stage. 

 The immediate cause of their death at this late stage is the development of 

 one or more black granules which cause death either because they are them- 

 selves toxic or because their substance is derived from an excessive malforma- 

 tion of organs essential to the further development of the fly. On the first 

 view, either the half amount of toxic body was insufficient to prevent the 

 gynandromorph from continuing its development, or the corresponding normal 

 parts of the female side counteracted this toxic effect; on the second view, the 

 lack of the essential organ on the male side was supplied by the normal organ 

 of the female side. 



No. 3674. August 9, 1917. A. H. Sturtevant. Text-figure 54 (diagram). 



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

 cut, vermilion, and for forked; the other X the gene for rugose. The father 

 was rugose forked. 



Description. The male parts of the gynandro- 

 morph constituted the left side of the thorax and 

 abdomen, as indicated by the smaller size, the sex- 

 comb, the smaller wing, and the male coloration of 

 that side of the abdomen. Testes were found in the 

 abdomen. The left wing showed the character cut. 

 The bristles of all male parts were wild-type. The 

 bristles of the female parts were forked, and this 

 character forms the most useful index of the divi- 

 sion-line. The entire head, including the bristles 

 above and below and around the left as well as the 

 right eye, was 'forked. The first and second leg on 

 the right side were forked, the third was not forked 

 and presumably therefore male. The bristles on 

 the right wing and on the right side of the abdo- 

 men were forked. There was no sex-comb on the 

 right side. The right wing was of female size and 

 not cut. Both eyes were red (not vermilion) and 

 also not rugose. 



Explanations. On the theory of two nuclei, one 

 nucleus contained a cross-over X with the gene for 

 cut and rugose, the other an X with the genes for cut 

 vermilion forked. The former nucleus was fertilized 

 by a Y sperm to produce the left side, the latter 



nucleus by an X sperm with rugose and forked to produce the female right 

 side. 



Left side. Right side. 



TEXT-FIGURE 54. 



ct 



rg 



ct 



f 



rg 



f 



An alternative explanation on the assumption of a single nucleus follows: 

 The mechanism in this case must be essentially the same as in cases I 92, 

 1333, and 2349 already given. The female parts were entirely forked, there- 

 fore two forked chromosomes were present. One of these could have come 

 from the father, whose X was rugose forked; the other X could have come from 





