92 The Third and Fourth Generation 



In the same way when two individuals are 

 crossed differing in three factors, the proportion 

 in the F^ generation is 27-9-9-9-3-3-3-1(3+1)^, 

 and there are eight pheno types (2.3) and 

 twenty-seven genotypes (3^) . When seven fac- 

 tors are involved, the proportion obtaining in 

 the different sorts of offspring in the F^ genera- 

 tion is (3+1)', and there are 128 phenotypes (2^) 

 and 2,187 genotypes (3^). So that if one were 

 to mate the albino rabbit with the factors BB, 

 EE, UU, II, AA, in its cells (no factor C is 

 present, so it is colorless) with the cream 

 mottled white whose cells have YY, CC, the 

 offspring wiU be gray. If these grays are 

 mated, 128 different sorts of rabbits, as far as 

 appearances go, might appear in the offspring, 

 and there would be possible more than 2,000 

 combinations of factors in their cells. This 

 illustration makes apparent the almost limitless 

 complexities involved in tracing the inheritance 

 of any character dependent on the interplay of 

 several factors. 



The following case will illustrate the presence 

 of two factors, either of which may cause the 



