THE LINKAGE OF TWO FACTORS IN DROSOPHILA. l8l 



The reciprocal cross gave the following results. 



Minature White Bl 9 by Wingless Red Gray cf 



\/ 

 Gray Red 9 and Miniature Gray White cT 



Females. 



GRL GWhL BIRL BIWhL GRM GWhM BIRM BIWhM GRW-g-s GWhW-g-s 

 220 45 88 45 96 197 46 62 113 95 



468 401 2o8 



Males. 



GRL GWhL BIRL BIWhL GRM GWhM BIRM BWhM GRW-g-s GWhW-g-s 

 225 96 120 35 92 201 41 99 131 105 



A A . * .. 



t *\ t ^ f \ 



473 433 236 



In this reciprocal cross there are ten classes each of females 

 and males. Each wingless class is made up (as in the other 

 cross also) of wingless long and wingless miniature. These, 

 if they could be separated, would give, in all, twelve classes of 

 males and females. 



The analysis of this cross is similar in principle to that given 

 above and can readily be reproduced by the method used for 

 that cross. How closely the yellow factor and that for Wing are 

 united will be determined later by suitable tests. 



On the assumption that factors are contained in chromosomes, 

 it will be apparent that this new case of linkage means that 

 both W and F are contained in a chromosome different from the 

 sex chromosome. 



After the foregoing results were completed, a doubt arose 

 as to whether we could with certainty detect black wingless 

 flies, even if present, since they would lack one of the most 

 characteristic features of black flies, namely, the wings. We 

 determined to test some of the F% flies by mating to long-winged 

 black flies, for we thought, at that time, that this would be a 

 legitimate test for the presence of black flies amongst the wingless 

 offspring. But while it is true that the appearance of black 

 offspring would be expected, if black flies were present, never- 

 theless the appearance of such flies does not in itself show that 

 black flies were actually present amongst the flies tested; for, 

 as the following analysis will show, crossing over may have 

 occurred when the gametes were produced, and yet no 2 black 



