SEGREGATION AND DOMINANCE 141 



(8 X 8) different zygotes, which corresponds to a 

 monohybrid raised to the third power (3 -f I) 3 . 

 These sixty-four zygotes group together in eight 



RSP RsP RSp Rsp rSP rsP r SP rp 



1 1 1 I I I 1 I 



RSP 



RSp 

 R*p 



rSP 



FIG. 47. Diagram showing the possible combinations in a guinea-pig 

 trihybrid of the F 2 generation. R, resetted coat ; r, non-rosetted coat 

 (absence of R) ; S, short hair ; s, angora hair (absence of <S) ; P, pig- 

 mented ; p, albino (absence of pigment). The eight possible triple 

 gametes of each parent are placed in the upper and left hand margins. 

 Each of the sixty-four squares represents a possible zygote or ferti- 

 lized egg, having received a triple gamete from each parent. 



different phenotypes and twenty-seven different 

 genotypes. 



The trihybrid cross with its resulting combinations 

 is well illustrated by Castle's work on guinea-pigs 

 which confirms the Mendelian hypothesis on an 



