58 



THE ORIGIN OF GYNANDROMORPHS. 



Doncaster's observations on binucleated eggs of Abraxas, where 

 both nuclei underwent separate reduction and fertilization, offer a 

 simpler explanation. On the other hand, it should be pointed out 

 that there should have been at least as many autosomal mosaics as 

 sex-linked mosaics produced by fertilization of binucleated eggs of 

 heterozygous mothers; and this does not seem to be the case. 



No. B. 90. June 17, 1912. C. B. Bridges. Text-figure 48 (drawing). 



Parentage. This gynandromorph appeared in F 2 from 

 the cross of rudimentary female to white miniature male; 

 that is, the mother (Fj female) carried rudimentary in 

 one X and white and miniature in the other; and the father 

 was a rudimentary (F^ male. 



Description. The individual seemed to be male through- 

 out. Both eyes were red. Sex-combs were present on 

 both forelegs. The right wing was long, and though 

 slightly deformed, was undoubtedly wild-type. The left 

 wing was a typical and perfect miniature rudimentary 

 wing. The abdomen was entirely male, and when mated 

 to a vermilion female the fly bred as a male, producing 

 abundant offspring. Several pairs of the wild-type daugh- 

 ters and vermilion sons of this mating were bred and all 

 produced red and vermilion in equal numbers, both in males 

 and females. That is, the gynandromorph bred as a wild- 

 type male carrying no mutant genes. Two of the F 2 pairs 

 are given as samples: 



TEXT-FIGURE 48. 



The drawing has been previously figured in Zeit. f. ind. Abst. und Verer., 

 1912, p. 324. 



Explanations. Simple elimination fails to explain this case, because the 

 characters of the fly, as well as its genetic behavior, show that it received two 

 different X chromosomes from its mother. For instance, miniature and 

 rudimentary were both present in the left (male) wing, which proves that the 

 X contained in these parts came from the mother and that crossing-over in the 

 mother must have occurred. Since the right wing was wild- type, its cells 

 must have contained a wild-type X, which likewise could only have come from 

 the mother. The FX and F 2 offspring of the gynandromorph showed that he 

 had such a wild-type X in the testis, which presumably came from the same 

 kind of cells as those of the right side. The offspring also show that the 

 gynandromorph had not received an X sperm from the father, which would 

 have given rudimentary offspring. Therefore the right side, at least, must 

 have come from a Y-bearing sperm, as further proved by the fact that the 

 gynandromorph was fertile as a male (males without a Y being sterile). 



On the view that the gynandromorph came from an egg with two nuclei, 

 a simple explanation of the result may be given. Before reduction, each 

 of the postulated nuclei must have had one white miniature X and one red 

 rudimentary X chromosome; after crossing-over and reduction in each, one 



