THE LINKAGE OF TWO FACTORS IN DROSOPHILA. 



IJ7 



winglessness is recessive to normal, that it is not sex-linked, and 

 that it has a lower viability than has the normal. The reciprocal 



cross gave: 



F 2 



" Winged 9 , 



Winged d", 



Pi F! 



Winged d* Winged 9 

 Wingless 9 Winged d" 



Wingless 9 , 

 Wingless cf , 

 Balloon 9 , 

 Balloon cf, 

 Miniature 9 



694 



639 

 146 

 127 



4 



i 



i 



Miniature cf, 24 



One at least of the grandparental wingless flies must have been 

 responsible for the miniatures, but the numbers are too small 

 to affect the other ratio seriously. There were 1,363 long (in- 

 cluding balloon and miniature) flies, and 273 wingless, or 4.9 to I. 



In a recent cross between long- winged 9 and wingless cf there 

 were present in the F 2 generation 1,081 long winged F 2 flies, 

 and 280 Wingless; a ratio of 3.9 to i. The reciprocal cross gave 

 in F 2 1,213 long-winged flies and 273 Wingless or a ratio of 4.4 

 to I . Compared with the preceding the results show that the 

 viability of the Wingless has not changed. It is curious to find 

 that the F 2 ratio in this cross and its reciprocal differ in both 

 instances in the same direction as in the earlier cross, but this 

 may be only a coincidence. 



LINKAGE OF THE YELLOW FACTOR, Y, AND THE WING FACTOR, W. 

 The linkage in question is most simply shown in the following 

 result: wingless Grays were mated to long-winged Blacks, and 

 gave in FI long-winged gray males and females. These inbred 

 gave in the F 2 generation: 



There are no wingless black flies in the F 2 generation, which 

 the Mendelian expectation calls for. Their absence can only be 



