8 THE THEORY OF THE GENE 



constitute a pair of contrasted characters giving a 3 to 1 

 ratio in the second generation, and that round and wrin- 

 kled constitute another pair. 



Yellovv/ Round 



^peen wrinkled 



Yellow (dree n) Round(wrinkled) 



Round 



wrinkled 



OP 



Yellow 

 ireen 



wrinkled 

 Round 



Q 



Fig. 7. 



Diagram to illustrate the inheritance of two pairs of Mendelian 

 characters, vi^., yellow-round and green -wrinkled peas. In the 

 lower part of the diagram the four classes of F2 peas are shown, 

 vis., the two original classes, yellow-round and green-wrinkled, 

 and the two recombination classes, yellow-wrinkled and green- 

 round. 



The offspring were yellow and round (Fig. 7). When 

 selfed, they produced four kinds of individuals, yellow 

 round, yellow wrinkled, green round, and green wrinkled 

 in the ratio of 9 : 3 : 3 : 1. 



Mendel pointed out that the numerical results found 

 here can be explained, if the separation of the elements 

 for yellow and for green is independent of that for round 

 and wrinkled. This would give four kinds of germ-cells 



