PRINCIPLES Of HEREDITY QQP, 



over between B and C occurs 3 per cent of the time (B and C are 

 three units apart), the percentage of crossing over between A and C 

 is found to be either 8 per cent or 2 per cent. If it is 8 per cent, C lies 



8 



to the right of B and the order is: A B^. If A and C are two units 



apart, then C lies between A and B and the order is: A C B. In all 



2 3 



such tests, the percentage of crossing over between the first and third 

 genes is either the sum or the difference between the percentages of 



p. Tall Tomoto Plant 



Spherlcol Fruit 



Dwarf Tomato Plant 

 Pear-shaped Fruit 



All Toll ond I Spherical Dwarf, Pear-shaped 



GAMETES 



t 



Non-crossovers Crossovers 



Toll 

 Spherical 



40 



Dwarf 

 Peor-shoped 



40 



Tall 

 Pear-shoped 



10 



Dwarf 

 Spherical 



10 



Figure 32.6. Diagram of a cross involving linkage and crossing over. The genes 

 for tall vs. dwarf plants, and spherical vs. pear-shaped fruits in tomatoes are linked; 

 they are located in the same chromosome. (Villee: Biology.) 



