SEX-LINKED LETHALS IN DROSOPHILA 



87 



a few red females individually, and continuing one of the lines 

 which gives a lethal sex-ratio and no red males or only an occa- 

 sional one. Records were made of the offspring of pairs from 

 some of these mass cultures of stock, and table 4, which is com- 

 parable with table 3, shows by the small number of red males 

 that none of the females used were cross-overs (B) free from lethal. 



TABLE 4 



Red-eyed females (A) carrying the lethal factor gave the following offspring when 

 mated in mass cultures to their white-eyed brothers 



If the analysis of this case is correct, the very small 'cross- 

 over' class of red males should be entirely normal and should be 

 unable to transmit the lethal characteristic. One of these males 

 (of L 9, table 3) was tested by mating him to a wild female. 

 There were produced 61 daughters and 48 sons, which is a fair 

 approximation of the 1 :1 ratio expected whether the father were 

 lethal or not. But if the father were a male which carried the 

 lethal, and by some means survived (i.e., if lethal were not invari- 

 ably fatal in its action) then all these 61 daughters should be 

 heterozygous for lethal and should give lethal ratios in F2. The 

 F2 generation was raised and consisted of 440 females and 377 

 males which is undoubtedly a non-lethal ratio. 



Another of these red-eyed males (from L 242, table 4) was 

 tested by mating to his red sisters heterozygous for lethal and 

 white (type A). The F] consisted of 59 red females and 24 

 white males. The absence of red sons shows that the mother 

 was of the type supposed, and the fact that there were twice as 



