February 23, 1922] 



NATURE 



243 



.wo of these red-eyed females are both hybrid for 

 rhite; one of them should be a non-disjunctional 

 »male (XXY) and repeat the same process. Such 



3LAR 



)DY 



RED 9 



the case. The females with three X's generally 

 but occasionally one emerges that can be iden- 

 led as such by certain peculiarities, and when the 

 ills of such a female 



studied it is found POLAR 



that three X's are pre- BODY 



sent (Fig. 6), Lastly, 



there is a male, XY, 



with red eyes, an " ex- ECC5 



ceptional male," since 



his mother had white 



eyes. He arises from a 



V-cgg fertilised by an X- 



bearing sperm — the so- SFERH 



called female - producing 



sperm. Here such a 



sperm makes a male be- 

 cause the combination of 



one X with the rest of the 



chromosomes is a male in 



these flies, quite irrespec- 

 tive of the origin of 



the X-chromosome. The 



result shows convincingly 



that the X-sperm normally gives rise to a female 



because it carries an X (the &^^ supplying another 



X), and not because its X is carried by a 

 ^ g " female-producing " sperm. 



^a^S^ There remains to be considered 



^^•^^ the case where the same series of 

 eggs is fertilised by the other kind 

 of sperm, the Y-bearing sperm. In 

 the lower line of Fig. 7 the outcome 

 is shown. Two kinds of males 

 appear, both white-eyed, but one 

 XYY and the other XY. The 

 is found to be a normal male; the 



former is expected, in some cases, to transmit both 



an X and a Y through his " female-producing " 

 NO. 2730, VOL. 109] 



sperm and give rise in this way to non-disjunc- 

 tional daughters (XXY). This, in fact, has been 

 shown to occur. 



The single class of 

 females that appears in this 

 series arises from the fer- 

 tilisation of the Y.'^-^^^ by 

 a "male-producing" (Y) 

 sperm. She has white eyes 

 and "breaks the rule." 

 She must, furthermore, 

 from her origin, be herself 

 a non-disjunctional female, 

 and, in fact, has been shown 

 to behave as such. Finally, 

 the YY individual in the dia- 

 gram is not found, and prob- 

 ably dies, as is to be ex- 

 pected, since it contains no 

 X-chromosomes. 



(3) From an entirely dif- 

 ferent source new proof 

 of the chromosome theory 

 has been found. This, 

 too, involves the sex-chromosomes. We have a 

 stock that gives results diametrically opposite 

 to ordinary sex-linked inheritance. The females 



^^ 



XXX ^ 

 Fig. 6. 



latter, XY, 



are yellow (recessive), and give, when bred to a 

 normal grey male, yellow daughters and grey 

 sons. A study of this stock by L. V. Morgan, 

 who discovered it, showed that all the results 

 could be explained by the assumption that two 

 X-chromosomes, bearing yellow, had become 

 stuck together. Sections of these females verified 

 the prediction. Two united X-chromosomes and 

 a Y are present in the yellow females (Fig. 8). At 

 maturation of the eggs both X's pass out together 

 into the polar body at the reduction division, or 

 else both remain in the ^^g. Thus the mature 

 eggs are XX or Y. Fertilised by a normal 

 "grey" X-sperm, the XX ^gg gives an XXX 

 grey female (which dies as a rule) and an XY 



