MENDELISM 



115 



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

 which confirms the Mendelian hypothesis on an extensive 

 scale. In Figure 21 dominant characters are repre- 



? t 



rSP-*- 



rsp- 



FIG. 21. 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, pigmented; p, albino (absence of pig- 

 ment). The eight possible triple gametes of each parent are 

 placed in the upper and left hand margins respectively. 

 Each of the sixty-four squares represents a possible zygote 

 or fertilized egg, having received a triple gamete from each 

 parent. 



sented by capital letters, while recessives or absences 

 are indicated by corresponding small letters. 



When a smooth, or non-rosetted (r), short-haired 

 (S), pigmented (P) guinea-pig is crossed with a 



