LETHAL FACTORS IN DROSOPHILA 



553 



Table 16 gives some of the counts of the descendants of 13, 

 2, 1,4 with white eyed males. 



TABLE 16 



Numbers 5 and 1 starred of table 15 show a decided decrease 

 in the number of white males. It looked as if the lethal factor 

 had crossed over into the chromosome carrying the factor for 

 white. To examine this, virgin females from number 1 were 

 mated to white eyed miniature males as shown in table 17. 



A lethal factor connected with the factor for white is evidently 

 present since all the white eyed females gave a 2 : 1 ratio. 



The red eyed sisters of the white eyed females in table 17a 

 should bear no lethal if, as the last table indicates, crossing over, 



