552 



HEREDITY 



for a part of the character, that, although they do segregate and 

 combine according to Mendelism, they form so many kinds of 

 combinations and thus so many kinds of individuals occur in the 

 second generation of hybrids that it is difficult to detect Mende- 

 lian ratios. For example, in the case of crossing the tall and small 

 varieties of Corn, it is assumed that the tall variety has a number 



FIG. 481. Inheritance of size and beards in Wheat. Parent types 

 (Turkey X Bluestem at the left and a hybrid No. 143 at the right) and be- 

 tween the parent types the Fi generation of the Cross. In the FI generation 

 the heads are somewhat intermediate in size and have short beards. After 

 Gaines. 



of factors for size that are not present in the small variety. Let 

 us suppose the large variety has four extra factors for size that 

 are not present in the small variety. These factors may be rep- 

 resented by A, B, C, and D. Since the tall variety is pure for 

 its height, its extra height over the small variety is due to the 

 presence of AABBCCDD, and the corresponding constitution of 

 the small variety is aabbccdd, in which the small letters represent 



