SEGREGATION AND DOMINANCE 



137 



Figure 44 presents a graphic representation of the 

 different combinations resulting from a dihybrid cross 

 following the checkerboard plan used in Figure 42 

 to illustrate monohybrids. 



The nine genotypes and four phenotypes which 

 result from a dihybrid cross are shown in the following 

 squares. 



Another illustration of dihybridism is shown in 

 Figures 45 and 46 which is based upon data fur- 

 nished by the Davenports. 1 In the matings given 

 here, dark or pigmented hair, represented by the solid 

 black circles, is dominant over light-colored, that is, 

 unpigmented or slightly pigmented hair, symbolized 

 by the open circles, while curly hair is dominant 



1 "Heredity of Eye-color in Man," Science, N. S. 26, p. 589, 1907; 

 " Heredity of Hair Form in Man," Amer. Nat. 42, p. 341, 1908. Daven- 

 irt, C. B. and G. C. 



