No. 576] 



VARIATION IN DROSOPHILA 



729 



and the father Beaded. This shows that although the 

 father transmitted his Beadedness more to his daughters 

 than to his sons, yet his Beaded sons also had the capac- 

 ity to affect their daughters more than their sons, and 

 these sons again repeated the phenomenon. Yet these 

 males could not have received their X-chromosome from 

 their father, unless non-disjunction (see Bridges, '13) 

 had occurred. In fact, to produce the results hero given 

 non-disjunction must occur in one half the females of 

 the Wild stock. Frequent tests with the Wild stock by 

 practically all of the students in the laboratory make it 

 certain that this is not the case. I also tested a consider- 

 able number of the females by mating them to sex-linked 

 mutants and found no non-disjunction. 



This apparent sex-linkage that does not follow the 

 "ordinary rules" of sex-linkage must be left for the time 

 being as one of the still unsolved problems. The only 

 possibility of explanation that occurs to me is that the 

 above-described effect would be produced if in the cyto- 

 plasm of the egg of the Beaded female something were 

 present which is absent in the egg of the normal female, 

 and to which the males are more responsive in their 

 development than are the females. This suggestion has 

 not a particle of cytological evidence to support it. Mor- 

 gan (1912<?) has suggested that the influence of cvtoplasm 

 may cause certain peculiar results obtained in crosses 

 between Miniature-winged and Rudimentary-winged flies. 



(b) Linkage to Sex-linked Genes 

 Matings of Beaded flies to flies with sex-linked char- 

 caters, including Vermilion and Vermilion-yellow, have 

 been made and the F 2 generation raised. No sign of 

 linkage was observed. The F 2 figures are given in Tables 

 X and XI. These cases definitely establish that there is 

 no gene for Beaded wings in the X-chromosome. 



Although no sex-linked gene for Beaded wings are 

 known, there has arisen in the Beaded stock by mutation 

 a fly with notched wings (Fig. 13) that proved to be 



