CORRELATED VARIABILITY. 



59 



It is clear that if this process of crossing of the hybrids 

 continues, the proportion of hybrids to the whole population 

 will diminish; for the share of pure-blooded forms breeds 

 true; while the originally equal share of hybrids is repeatedly 

 halved. 



If the hybrid is crossed with one of the parents instead of 

 with another hybrid, we will get 



(1) (d + r)d=d, d+d, r, and 



(2) (d + r)r=d, r+r,r. 



In (1) all of the progeny will appear of the dominant type. 

 In (2) one-half will appear of that type. This again agrees 

 with experiment. 



Second Case. The two parents differ in respect to two 

 characters case of dihybrids. Imagine a lot of ripe germ- 

 cells with the antagonistic qualities of any pair separated 

 according to the second principle stated at the outset. A 

 indicates the one pair of qualities and B the other; then we 

 shall have nine classes of zygotes, the proportion of each of 

 which is as follows: 



A. 



B. 6.25%d, d; 12.5%d, r; 6.25%r, r. 

 A. 50%d, r 



B. 12.5%d,d; 25%d, r; 12.5%r, r. 



A. 25%r, r 



B. 6.25%d, d; 12.5%d, r; 6.25%r, r. 



