THE ORIGIN OF GYNANDROMORPHS. 65 



The two anterior bristles above the right eye and all the bristles below it were 

 forked, agreeing with the forked bristles present throughout the rest of the 

 right side on legs, thorax, and abdomen. A sex-comb was present on the 

 right fore-leg and all male parts were smaller. The right side was female 

 throughout, with normal bristles and a red eye. The genitalia were half- 

 and-half. In the sections of the abdomen an ovary could be identified on one 

 side, less certainly on the other. The body-color of both male and female 

 parts was wild-type throughout, with no yellow. 



Explanations. On the theory of the binucleated egg, one nucleus contained 

 an X with the genes for lethal and ruby, the other nucleus a cross-over X 

 with the genes for lethal, ruby, and forked. The former fertilized by X sperm 

 with yellow eosin forked, produced a female left side with only wild-type 

 characters; the latter, fertilized by a Y sperm, gave the ruby forked male 

 side. 



Left side. Right side. 



y w< f I, r b f 



i r b 



An alternative view based on a single nucleus is as follows: Simple elimina- 

 tion fails to explain the case, since the male parts that are forked are not- 

 yellow and not-eosin, as might be expected, but instead were ruby. Since 

 ruby was present only in the mother, the male parts must have come from a 

 lethal 7 ruby forked cross-over chromosome produced by the mother. That 

 the other X chromosome of the zygote was not the yellow eosin forked X of 

 the father is proved by the not-forked character of the female parts. It 

 seems certain that both X chromosomes of the zygote came from the mother, 

 that is, that the egg was a non-disjunctional XX egg. This must have been 

 by primary non-disjunction, since the pedigree is fully known and no other 

 exceptions were produced. Another fact points to the same conclusion, 

 namely, that these X's were both cross-overs, and, as Bridges has shown, both 

 X's of secondary exceptions are always non-cross-overs. What occurred, then, 



y w e f 



was crossing-over in the '. ! : ' female between the 



li r b 



loci ruby and forked. Owing, perhaps, to some entanglement in the process of 

 crossing-over, the chromosomes were unable to separate in time for the reduction 

 division and both were retained in the egg. This egg, containing a yellow eosin 

 X and a lethal 7 ruby forked X, was fertilized by a Y sperm. At the first 

 segmentation divisions one of these maternal yellow eosin chromosomes was 

 eliminated, giving a gynandromorph whose male parts were lethal 7, ruby, 

 and forked. 



Left side. Right side. 



li r b f IT r b f 



y w e f 



A very interesting point in connection with gynandromorph 4241 is the 

 fact that a male part, which must be assumed to have the lethal 7 gene, was 

 able to live when associated with the not-lethal partner in the gynandromorph. 

 This is, however, understandable when the nature of the action of the lethal 7 



