LETHAL FACTOES IN DROSOPHILA 



551 



TABLE 14 

 Ten sisters by brother No. 1 



heterozygous for white. The females heterozygous for white 

 when mated to white eyed males would produce equal numbers 

 of red eyed and white eyed males and females (table 15) except 

 where the lethal may have crossed over to the factor for white 

 (as was the case in numbers 5 and 1, starred in table 15).- The 

 females heterozygous for lethal when mated to the white eyed 

 males produce the 2 : 1 ratio, also indicated in table 15. 



Matings were, also, made between the three males and daugh- 

 ters of the sisters of the males with results as follows: 



(13, 2, 1, 4; Female by W male')F; Female by No. 2 male 



2 The other class resulting from such crossing over should contain neither the 

 white nor the lethal, and one such female is recorded in table 15. 



