A THIRD SEX-LINKED LETHAL 



323 



early hatches of the cultures/ On the other hand, the proportion 

 of males is the same as in the other cultures. 



In the last columns of the three preceding tables the percentages 

 of cross-overs between white and the lethal are given. If these 

 are tabulated they show bimodal curves (diagram 3). 



fij 



y^ 



n 



\. 



_^ 



B 



Diagram 3 Bimodal curves from the grouping of the linkage values from tables. 

 A, grouped 9 + 10, 11 + 12, etc. B, grouped 8 + 9, 10 + 11, etc. 



All the data taken together suggest the following interpretation. 

 If an original female that gave rise to the 71 :3 ratio had two lethal 

 genes that are not allelomorphs, one in each of her sex chromo- 

 somes, all of her sons should perish except those few which resulted 

 from crossing-over. The three males would be these cross-overs 

 and indicate the amount of crossing-over that had taken place 

 (provided their number is doubled, for the other equal class of 

 cross-over males perished). Using the 71 females as the number 

 of all the expected males and dividing this into 6 would give the 

 percent of cross-overs, namely, 8 per cent. 



In the second place, all the 71 daughters should be lethal- 

 bearing, except 8 per cent corresponding to the males that sur- 

 vive. In fact, all of 34- females tested were lethal. 



* If the first-hatched daughter had been fertilized by the father before they 

 were removed (as virgins!) this result can be explained. In the next generation 

 no repetition of the occurrences was seen. 



