SEX-LINKED INHERITANCE IN DROSOPHILA 83 



CROSSES INVOLVING TWO SEX-LINKED CHARACTERS 



In the following crosses black and yellow body-color, white and 

 red eyes are involved. In these cases there are only two sex- 

 linked factors, viz., the factor for black and the factor for red 

 (and their respective absences). In reahty, it is the color-pro- 

 ducer, C, and not red color, R, that is the factor involved in the 

 eye-color inheritance; but with this explanation no misunder- 

 standing will arise if we use the symbol R for red eye and W for 

 its absence. 



In the first case long winged, white eyed, black females were 

 crossed with long winged, red eyed, yellow males. If all the 

 female classes were realized in F2 there would be many more 

 classes than actually appear, but owing to the linkage between 

 W and B from the grandmother, and R and b from the grand- 

 father there will be only eight large classes. The smaller classes 

 represent the breaking of the linkage or 'crossing-over:' 



LRY cf by LWB 9 



Ft 



LRN 9 = 244 

 LWN c^ = 253 



The analysis is as follows. The factor for Brown (Br) is here 

 omitted : 



