RULES AND RATIOS OF INHERITANCE 



213 



heterozygote of the type shown in figure 45, Fi. Its two 

 chromosomes may be designated A — B and a — h. 



Assume that the distance between the two gene pairs is 



a 



a 



b 



b 



Fl 



Gametes 

 from 



Fl 



.9 



.1 



Figure 45. Diagram to illustrate the ratios produced in F2 when 

 parents differ in two gene pairs located in the same autosome. See 

 text. 



such that exchange takes place in one-tenth of all cases, the 

 exchanges yielding chromosomes carrying A — b and a — B, in 

 place of the original A — B and a — b. Then in nine-tenths of 

 all cases the chromosomes retain the original constitution, 



