SEX-LINKED LETHALS IN DROSOPHILA 



109 



TABLE 21 



(From No. n of table 10) 



ratio and from this lot a few females were bred to eosin ver- 

 milion males. Their offspring are recorded in table 21. The 

 data appear to verify the conclusion that the second lethal has 

 gone while a disturbance of the sex-ratio remains. Can these 

 results be interpreted to mean that the second lethal disappeared, 

 and a third lethal, L3, that was present and gave the original 

 high ratio of 78-16, has been retained? 



If such a third lethal is here affecting the sex-ratio and if it 

 lies beyond (to the right) of miniature as shown in figure F, 

 then the deficient class is eosin long males. If the lethal kills 

 then the only representative of that class will be double cross- 

 overs and should be infrequent in proportion as L3 is close to M. 

 In fact, in a large number of cases in the table, the I3 class, is 

 behind the other male classes. In order, however, for the double 

 cross-over class, eosin long, to be as frequent as appears in the 

 table, the distance of L3 to M would have to be very long indeed. 

 In order to calculate this distance it would first be necessary to 

 find out from table 20 those classes in which the factor occurs, 

 but it is impossible to do this, for there are too many cases whose 

 position is uncertain. If we make a single attempt to pick out 

 such cases on the basis of the deficiency in the eosin long class 

 we find that the most frequent class is that with a ratio of 1.5:1 

 and not 2:1 or more as would be the case if a lethal like the other 

 two lethals is here present. 



