OF MUTANT CHARACTERS. 



243 



was that of the second chromosome, a cream male (from pure stock) 

 was out-crossed to a curved female, curved being a recessive wing- 

 character whose gene is known to belong to the second chromosome 

 (Bridges and Sturtevant, 1914). A pair of FI wild-type flies inbred 

 gave the results of table 90. 



TABLE 90. F 2 from the cross of cream II male to curved female. 



Since cream only shows itself where eosin is already present, we may 

 disregard all the flies of culture 70 except those with eosin eyes. These 

 eosin flies are obviously in the ratio 2:1:1:0 which is expected if the 

 cream gene is in the second chromosome, through the flies are too few 

 to prove the point. 



TABLE 91. Pi, cream II c? X eosin black 9 . FI heterozygous 

 cream 9 X FI heterozygous cream cT . 



A more efficient experiment than this last was carried out by making 

 all the flies of the experiment eosin, in which case the 2:1:1:0 

 ratio involved all the offspring rather than only a quarter, as in culture 

 70. A stock of eosin black was made up (black being a second-chro- 

 mosome mutant) and a female of this stock was outcrossed to a cream 

 II male. The FI and F 2 results are given in table 91. All of the FI 

 flies and half the F 2 flies were of the intermediate color of the heterozy- 

 gous cream. In the F 2 these intermediates were classified along with 

 the pure eosins, so that the cream was treated as though a strict 

 recessive. 



