SEX-LINKED LETHALS IN DROSOPHILA 



95 



sex-chromosome carrying the factors gray (Y) non-lethal (L2) 

 and eosin (w). The two non-cross-over classes, the four single 



y liW 



y liw 



X 



YLw^ 

 y liw 



X 



YL,w^ 



xx 



YL,w' 



Figure B 



cross-over classes, and the two double cross-over classes of game- 

 tes are as follows (see also fig. B). 



Non-cross-overs . 



Single cross-overs 



Double cross-overs. 



y li w — fdies) 



Y Li w® — gray eosin 

 y L w^ — yellow eosin 



Y 1 w —(dies) 



y 1 w® — (dies) 



Y L w — gray white 

 y L w — yellow white 



Y 1 w*^ —(dies) 



If we take the sum of all the male classes (668 + 4) and divide 

 into the single cross-over class of flies (4) we get a percentage of 

 0.6 to represent the distance of the new lethal from yellow. 

 This corresponds with the calculated percentage of the original 

 lethal which is 0.7. In other words, this lethal lies near yellow 

 and white — somewhat nearer to white. The single cross-over 



