368 



CALVIN B. BRIDGES 



TABLE 23 



The B. C. offspring given by Fi eosin star dichaete sons, from the outcross of a pinkish 

 female to a star dichaete male, when hack-crossed to pinkish females 



1916, 8/25 



5029 I ^ 



52m(J, 

 Total. 



NON-CROSSOVERS 



(Eosin) 

 star 



(Eosin) 



star 

 dichaete 



10 

 17 



22 

 20 



12 

 13 



20 

 2€ 



69 



65 



Pinkish 



Pinkish 

 dichaete 



10 

 16 



18 

 21 



9 



22 



21 

 26 



65 



78 



CROSSOVERS (in male) 



Star 

 pinkish 



Star 

 pinkish 

 dichaete 



(Eosin) 



(Eosin) 

 dichaete 



region of the second chromosome. Fortunately, one advantage 

 of the test just described is that it left us in possession of females 

 heterozygous for star and for pinkish, and a back-cross test 

 showed (table 24) that there is very free crossing over between 

 star and pinkish. Pinkish is known, therefore, to be in the 

 right-hand end of the second chromosome in the neighborhood 

 of arc, speck, balloon, etc. Had the test given almost no crossing 

 over between star and pinkish, we should have known that the 

 gene for pinkish was in the left end, but this was not the case. 

 A test as to whether the pinkish gene would have any visible 

 effect in the absence of eosin showed (table 25) that in a very 

 small per cent of the flies homozygous for pinkish there is a very 

 slight dilution. This dilution is, however, so slight that rarely 

 could one be sure that the effect observed is due to dilution rather 

 than to the slight normal fluctuation of the red. 



TABLE 24 



The B. C. offspring given bij a star female from table : 



male 



when back-crossed to a pinkish 



