62 THE ORIGIN OF GYNANDROMORPHS. 



the eosin vermilion X and a Y. The gonads developed from an eosin cell as 

 shown by the FI and F 2 results of his breeding test. 



Zygote. Left i>ide. Right side. 



W e V W' V 



w* w e 



No. 1333. February 19, 1915. C. B. Bridges. Text-figure 51 (diagram). 



Parentage. The mother was a wild-type XXY female, carrying the genes 

 for eosin in one X and for vermilion and forked in the other. The father was 

 bar. 



Description. The fly was female throughout, except for the left eye which 

 was round (not bar) and red (not eosin or vermilion). The eye has been 

 examined repeatedly at different times since the mosaic was on hand, and the 

 eye is undoubtedly, not-bar and is of the right size for a male. The right 

 eye was heterozygous bar. There were no forked bristles present around the 

 left eye elsewhere. The female was mated to a sable forked male and pro- 

 duced: No. 1555 forked females, 11; forked bar females, 0; bar females, 18; 

 wild-type female, 1; vermilion forked males, 18; bar males, 6; vermilion bar 

 males, 3; forked males, 2. 



Explanations. On the hypothesis of a binucleated egg, one nucleus after 

 reduction contained a cross-over wild-type X and the other a non-cross-over 

 vermilion forked X chromosome. The former fertilized by a Y sperm gave 

 rise to the wild-type (male) left eye; the latter fertilized by a bar X sperm 

 gave rise to the rest of the fly. 



Left side. Right side. 



V f 



B 



The following alternative possibilities may be considered: The simplest 

 possible explanation is that this is a mosaic or somatic mutation that the 

 bar gene in the cell that gave rise to the left eye reverted to not-bar, or to an 

 allelomorph which gives a small round eye. If, as is more probable, this 

 mosaic is a gynandromorph arising by chromosomal disturbance, the ex- 

 planation is like that for No. I 92, i. e., the egg arose by equational non-dis- 

 junction and contained a non-cross-over vermilion forked X and a cross-over 

 wild-type X. This egg probably did not contain a Y, as evidenced by the 

 lack of exceptions among the sons of the mosaic, and as is possible in accordance 

 with the assumption of equational non-disjunction, for equational non-dis- 

 junction, even when occurring in a female with a Y, is probably always primary. 

 One eye was clearly heterozygous bar; hence it is known that the XX egg 

 was fertilized by an X sperm carrying the gene for bar. This XXX zygote 

 would ultimately die, unless at an early stage the XXX condition was cor- 

 rected by reduction or elimination. Double elimination or somatic reduction 

 in a cleavage-cell would save the individual, but turn it into a gynandromorph. 

 The other X chromosome, wild-type, passed into the sister cell and gave rise 



