370 



CALVIN B. BRIDGES 



eyes were of other than the normal red of the wild-type. On 

 the other hand, among the eosin-eyed offspring about a quarter 

 were of the light color, and this without noticeable sex limitation, 

 that is, the females and males were diluted to the same propor- 

 tionate extent. On analyzing the distribution of the cream with 

 respect to the second chromosome dominant star and the third 

 chromosome dominant dichaete, it was seen that the gene for 

 the cream is contained in the second chromosome, for the cream 

 appeared only in the flies that were not star, all the flies being 

 either star or cream and none being both star and cream or 

 neither, which condition is in accord with expectation from the 

 lack of crossing over in the male. The 2:2:0:0 ratio observed 



TABLE 26 



The F2 offspring given 6?/ F\ wild-type females and Fi eosin star dichaete males from 

 the outcross of a cream c female to a star dichaete male 



1 Culture 5588 and 5631 produced 'apterous'as the result of a fresh mutation 

 which took place in the cream c stock (Metz, Am. Nat., '14, pp. 675-692). 



in the case of star and cream c is in sharp contrast to the 1:1:1:1 

 ratio in the case of cream c and dichaete in the same experiment. 

 There were as many creams among the dichaetes as among the 

 not-dichaetes, as is expected from the free assortment of genes 

 in different chromosomes. 



Up to this point there had been no confusion possible among 

 the various modifiers; for the effects produced had been different 

 in one or more of the following respects: in degree, in color tone, 

 in dominance, in specificity, in interaction with other mutants, 

 in the chromosome concerned, or in the locus within that chromo- 

 some. In the case of cream c, there was the chance of confusion, 

 since in tone cream c is not different from cream b, though in 



