2O4 



MILDRED HOGE RICHARDS. 



(or rose). Since rose and salmon are indistinguishable pheno- 

 types, the results correspond closely with the expectation as 

 will be seen in the following table. In these results the classes 

 rose, salmon, and the double recessive rose salmon are all alike 

 in appearance and therefore could not be separated. 



This is another case similar to the well known one of the white 

 sweet peas, in which two different genes produce the same 

 phenotype. 



Since rose was not linked to the first chromosome group, it 

 was crossed to vestigial of the second, and to sooty of the third 

 group. The first cross gave a 9 : 3 : 3 : I ratio, and the second 

 a 2 : i : i ratio, as follows : 



Rose X vestigial 



Fi Wild-type 



F 2 Wild-type 1046, vestigial 257, rose 345, vestigial rose 104. 



Rose X sooty 



F! Wild-type 



F 2 Wild-type 727, rose 278, sooty 330, rose sooty o. 



These results show that there is free interchange between the 

 genes for rose and for vestigial, but that rose and sooty are in 

 the same chromosome pair. Rose is therefore a member of the 

 third chromosome group. Its linkage relations were determined 



1 Expectation is calculated by the checkerboard method, on the basis of 16 F? 

 individuals. 



