SEX-LINKED LETHALS IN DROSOPHILA 



89 



TABLE 5 

 Offspring of while-eyed daughters of lethal flies mated in pairs to white-eyed males 



On the scheme of locating the factors that we have employed, 

 0.6 per cent of crossing-over means that lethal lies at a distance 

 of 0.6 of a unit from white, but in which direction from white is 

 not so far shown. In order to determine on which side of white 

 the lethal lies, it is necessary to know the distance between lethal 

 and another known point of the chromosome. The second point 

 chosen was the factor for miniature wing. Two daughters (type 

 A, from L 9) were mated to eosin miniature'' males and gave the 

 following Fi offspring (table 6). 



The red-eyed, long-winged daughters (from table 6) were mated 

 to their white-eyed, long-winged brothers with the following 

 F2 results (table 7) . 



^ Eosin is allelomorphic to white, so that any linkage results given by white 

 or by eosin have the same value, and can be combined. The female which is 

 white-eosin in composition is distinguishable from the pure eosin. 



