108 



CELL HEREDITY 



car \ 

 B 



car 

 B 



Female parent 



car 



4+ + 



U 



Noncrossover Crossover 



chromosomes chromosomes 



(a) 



Knob 



•515^1 



Parental cross 



wx^mm-wx 



II 



Class 1 



Class 2 



Noncrossover 

 progeny 



It 



Wx—^W-wx 

 II 



Class 3 



it 



II 



wx-^^wx 



Class 4 



Crossover 

 progeny 



(b) 



FIGURE 4.8. The correlation of cytological exchange with genetic recombination: 

 a demonstration that physical exchange between chromosomes is involved in crossing 

 over. 



(a). Drosophila experiment in which the X chromosomes of the female parent are 

 labeled both genetically and cytologically. Examination of progeny flies exhibiting 

 genetic recombination between cor and 6 showed that car+ flies had neither the 



