186 



THE SECOND-CHROMOSOME GROUP 



the mating was accordingly arranged so that a cross-over anywhere 

 within this whole distance would give the required triple form. That 

 is, black purple and purple vestigial were mated together and the 



resulting purple offspring f^r" - - ) 



\~T~ Pr V g / 



were inbred. The F 2 black 



TABLE 38. PI mating, black purple vestigial cf X wild female; B. C. mating 

 FI wild-type 9 X black purple vestigial cf . 



TABLE 39. PI, black X purple vestigial; B. C.-test of Fi 99 singly. 



TABLE 40. P l} black vestigial X purple; B. C. test F l 9 9 singly. 



purples and purple vestigials were crossed together in several mass- 

 cultures, and in F 3 some triples occurred, showing that some of both 

 kinds of F 2 flies used had come from cross-over eggs. A better method 

 would have been to back-cross the FI female by a black-vestigial male. 

 In this case every black vestigial cross-over would be known to be of 



the composition ( b Pr v \ and these inbred would give the pure 

 \ b + v g / 



