A THIRD SEX-LINKED LETHAL 



319 



Vermilion females were out-crossed to club males. From those 

 sets that gave a sex-ratio, daughters (red eyed) were mated singly 

 to their vermilion-eyed brothers. About half of the females gave 

 no sex-ratios, as follows: 



The cultures that gave sex-ratios follow (table 3) : 



TABLE 3 



The smallest class of males is vermilion, which we assume there- 

 fore to be the double cross-over class. Since the lethal went in 

 with the vermilion female one of the chromosomes of her daughter 

 will contain the genes for lethal and for vermilion ; and the homol- 

 ogous sex chromosome will contain the gene for club. The rela- 

 tion of the two chromosomes with the normal allelomorphs of 

 these genes are shown in diagram 2, 



q 



V 



X 



X 



Ci 



Diagram 2 



In order that vermilion become the double cross-over class the 

 lethal must be between club and vermilion, as in the diagram. 

 The chromosome distances calculated from the results are as 

 follows : 



Club lethal III 13.0 



Lethal III vermilion 5.4 



Club vermilion 18.0 



