No. 584] HEREDITY AND ITS MEANING 



473 



if C should become c, and the chromosome pair take the 

 form ABC and abc, there are definite relations between the 

 three determinants. Breaks in correlation occur, and this 

 ratio is constant, so that if given the percentage of breaks 

 of correlation between "A" and "C" and "B" and "C," 

 the percentage of breaks between "A" and "B" can be 

 predicted. If there is a break in the correlation between 

 "A" and "C" 30 times in 100, and a break between "B" 

 and ' ' C " 10 times in 100, then there will be breaks in the 

 correlation between "A" and "B" 20 times in 100. 



Likewise, the determinants in the second pair of chro- 

 mosomes are coupled together in their inheritance. D, E 

 and F have each their peculiar linkage to the other, a link- 

 age that remains comparatively constant. Yet the de- 

 terminants in the second pair of chromosomes are entirely 

 independent from those in the first pair in their inheri- 

 tance. For example, if, as shown in Fig. 5, "A" should 

 become "a" in either member of pair number one, and 

 "D" should become "d" in either member of pair number 

 two, Mendeliau dihybridism would result. Furthermore, 

 if "A" and "D" should each have the function of affect- 

 ing the same general character complex in somewhat the 

 same manner, there would be an apparent 15 : 1 ratio if 

 dominance were complete or a series of types ranging 

 from the type of one grandparent to that of the other, if 

 dominance is lacking. 



These are the main features that have been established 



