CHROMOSOMES AND GENES 



51 



triplo-TV is bred to an eyeless fly two kinds of offspring 



result (Fig. 33). Half are triplo-IV's, and half have the 



normal number of chromosomes, as shown in the diagram. 



If, now, one of these triplo-IV flies is back-crossed to 



Triplo-nr 



Gametes 



O O ^'^'='"' 



r. 



>^ 



Fj Triplo-U 



fi^gg' 



o o 



o o 



,°8 



S Wild Type 



1 Ei^eless 



Fig. 33. 

 Diagram of a cross between a triplo-IV fly with normal eyes and 

 a normal diploid fly, pure for eyeless. In the lower half of the 

 diagram an Fj triplo-IV fly (whose gametes are represented in 

 "Fi eggs") is crossed to a diploid eyeless fly (whose "eyeless 

 sperm" is represented by the open circle), giving five kinds of 

 flies in the ratio of five wild type eyes to one eyeless. 



