SEX-LINKED LETHALS IN DROSOPHILA 93 



Furthermore, there were no yellow white males in the 2 :1 ratios, 

 although as many are expected as gray red, unless some disturb- 

 ance is present. In fact, in the other ten pairs as seen below, 

 the number of males in these two contrary classes correspond 

 numerically (gray red, 649; yellow white, 621). The absence 

 of the yellow white males aroused a suspicion that a sex-linked 

 lethal was present, close to the yellow and the white factors. 



females males 



gray yel. gray yel. gray yel. gray yel. 



red white white red red red white white 



707 687 5 10 649 9 5 621 



About a dozen of the yellow white females (from the lot giv- 

 ing 2:1 ratios) were bred to eosin males (stock). Only four pairs 

 produced offspring. The records are as follows: 



white yellow 



eosin 9 white cf 



Bi 11 9 



Gi 25 5 



Go 26 14 



Ci 36 21 



The twelve pairs were afterwards transferred to one bottle 

 and gave as a mass result: 



White-eosin 9 ^ Yellow white cf 



101 33 



Matings (in pairs) were made between virgin females from 

 Bi, Gi, G2, Ci, and also some from the mass cultures with eosin 

 males of stock. The results are given in table 9, where it will 

 be seen that there are two kinds of females — some giving a 1:1 

 ratio (with the yellow white male class fully represented) and 

 others giving a 2 :1 ratio (with the yellow white male class entirely 

 absent). Of the females tested 13 were non-lethal bearing, and 

 10 were lethal bearing. This is the expectation if the 2:1 ratio 

 is due to a sex-linked lethal. If we return to the original series 

 Bi, Gi, Go, Ci we find that only one daughter of Bi was tested. 

 She was non-lethal bearing. Probably Bi was non-lethal as the 



■* Also one mosaic. 



