364 



CALVIN B. BRIDGES 



TABLE 20 



The B. C. offspring from the Pi viating of an eosin star dichaele male to a cream b 

 female and the hackcrossing of the Fi eosin star dichaett male to cream b 



females 



1916, 9/8 



5155 < J 



5409J^ 

 Total. 



NON-CROSSOVERS 



Eosin 

 star 



Eosin 



star 



dichaete 



20 

 19 



14 

 14 



25 

 21 



21 

 15 



67 



82 



Cream b 



Cream b 

 dichaete 



26 

 21 



18 

 17 



12 

 26 



26 

 24 



82 



77 



CROSSOVERS (in MALE) 



Star 

 cream b 



Star 

 cream b 

 dichaete 



Eosin 



Eosin 

 dichaete 



not. If, on the other hand, the cream were in the third chromo- 

 some, then none of the B.C. dichaetes should be cream, while 

 the star and cream should assort at random. The experiment 

 proved that the gene for cream b is in the second chromosome 

 (table 20). 



An (eosin) star female and a cream b male selected from the 

 B.C. offspring gave in the next generation the amount of crossing 

 over between star and cream b (table 21). This value of 22.1 

 includes some double crossing over, and the corrected or 'map' 

 distance is probably about 22.5. The chances are in favor of 

 the cream b locus being to the right of star, since star happens 

 to occupy the leftmost of the known loci. 



TABLE 21 



The B. C. offspring given in F3 by an eosin star female and a cream b male from 



table 20 



