58 



THE ORIGIN OF GYNANDROMORPHS. 



Doncaster's observations on binucleated eggs of Abraxas, where 

 both nuclei underwent separate reduction and fertihzation, ofifer 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 F2 from 

 the cross of rudimentary female to white miniature male; 

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

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

 was a rudimentary (Fi) 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 F2 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 Fi and F2 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 



