294 



CALVIN B. BRIDGES 



Meanwhile, the purple curved test, while less satisfactory 

 because of the longer interval with the attendant correction 

 necessary for double crossing over, was more readily handled, 

 and this led to a rapid accumulation of data on the purple curved 

 crossover value. The black purple curved triple recessive was 

 obtained (May, 1913), and the back cross itself carried out. 

 Thirteen of the Fi wild-type daughters form the cross of black 

 purple curved to wild-type were tested by back crossing singly to 

 males of the triple form. These same parents were, at the end 

 of ten days, transferred to fresh culture bottles and second 

 broods were raised. The details of the data of these cultures 

 have already been published (Bridges, '15) and we need repeat 

 here only the totals for the first broods (table 18). 



TABLE 18 



The total offspring of the first broods of the black purple curved X wild hack ross 

 {details published Jour. Exp. Zool., July 1913, p. 8) 



August 24, 1913. 



21.3 



The second broods confirmed on a large scale the fact first 

 brought to Ught in the purple vestigial back crosses (tables 7 

 and 8), that in the second chromosome the amount of crossing 

 over changes with the age of the mother (Bridges, '15). 



The numerical relations in the first broods of this experiment 

 confirmed the position of curved as already mapped. A map of 

 the second chromosome was constructed on the basis of the data 

 then on hand (October, '13), and was as follows: 

 b pr vg c 



(W) 5:3 17:5 25IO 



The black purple curved back cross was carried out in only 

 one of the four possible ways, and is therefore unbalanced. 

 However, the results showed that inviability was neghgible. 

 The little deviation from expectation can be attributed to 

 curved, which appeared to the extent of 97 flies for every hundred 

 expected. 



