THE ORIGIN OF GYNANDROMORPHS. 57 



Explanations. — A cross-over X carrying the gene for white but not for bar 

 was present in the egg, which was fertihzed by the X sperm carrying the 

 gene for miniature. Elimination of this paternal X left a cell with the white 

 X to determine the male parts. In the early cleavage there must have been 

 extensive shifting of the nuclei to produce the observed mosaic of female and 

 male parts. 



w V 



m 



No. 16240521114. Selection Experiment. August 2, 1916. T. H. Morgan. 



Plate 4, Figure 2 (drawing). 



Parentage. — The gynandromorph arose in a "selected" notch stock in 

 which the female carried notch in one X and eosin and ruby in the other. 

 The father was eosin ruby. 



Description. — The gynandromorph was "quartered," being male in the 

 anterior left section and also in the posterior right section, and female in the 

 two other sections. The left eye was mainly eosin ruby, but had a small 

 section of red (female) pushed in from the rear. The left side of the thorax 

 was male, as evidenced by the sex-comb and the shorter wing. The right 

 side of the abdomen had male coloration above and below, and the genitalia 

 were male on the right side and female on the left. The abdomen seemed to 

 have a pair of ovaries when examined, but the sections made later were too 

 poor to confirm this. The right eye was red and the right wing notch. 



Explanations. — ^An egg carrying the gene for notch was fertilized by a sperm 

 carrying the genes for eosin and ruby. Elimination of the maternal notch 

 X occurred at the first division, leaving the eosin ruby paternal X to determine 

 the character of the male parts. The products of the second division rear- 

 ranged themselves so that sister cells took part in the development of opposite 

 sides of the body. This is only a little more extreme than the usual rear- 

 rangement and shifting of parts (see patch of red in left eye). 



10* n w n 



SPECIAL CASES. 



The following cases were brought together because they could not 

 be explained simply by the theory of ehmination. Analysis showed 

 that in each of these cases there were present two different chromo- 

 somes, both derived from the mother. Non-disjunction obviously offered 

 an explanation for this fact. But the application of this hypothesis 

 required the additional assumption of "somatic reduction" to explain 

 the gynandromorphism. This means that at an early division the 

 two X's derived from the mother separate without division. On 

 the other hand, if we assume for these cases that both sex chromosomes 

 leave a daughter half at the mid-plate (double elimination) the assump- 

 tion just stated is avoided. Until further explanation is obtained 

 these two interpretations may be given as alternatives. 



