PHENOMENA OF INHERITANCE 245 



differ in many characters, and this leads to a 

 great increase in the number of types of off- 

 spring in the F 2 generation. But however 

 many pairs of contrasting characters the par- 

 ents may show each pair may be considered by 

 itself as if it were the only contrasting pair, 

 and when this is done all the offspring may be 

 classified according to the regular Mendelian 

 formula given above. 



But when two or more contrasting charac- 

 ters of the parents are followed to the F 2 gen- 

 eration many permutations of these characters 

 occur, thus giving rise to a larger number of 

 types of individuals than when a single pair of 

 characters is concerned. When there is only 

 one pair of contrasting characters there are 

 usually but two types of offspring apparent in 

 the F 2 generation, viz., dominants and reces- 

 sives in the ratio of 3:1 (Fig. 52) ; where there 

 are two pairs of contrasting characters in the 

 parents there are four types of offspring in 

 the F 2 generation in the ratio of (3 : l) 2 = 

 9 : 3 : 3 : 1 ; when there are three pairs of con- 

 trasting characters in the parents there are 

 eight types of offspring apparent in the F 2 



