HYPOTHESIS OF MULTIPLE FACTORS 195 



Fig. 131, top left. For four independent size-factors, the F2 

 classes would be more numerous still, viz., nine (Fig. 131, 

 right), and the extreme ear-size of either grandparent would 

 be expected to reappear in only one out of two hundred and 

 fifty-six offspring, while considerably more than half of them 

 would fail within the closely intermediate classes included 

 between five and one-half and six and one-half inches, the 



I 



I 



Fig. 131. — Diagrams to show the number and size of the classes of individuals to 

 be expected from a cross involving Mendelian segregation without dominance. One 

 Mendelian unit involved, bottom left; two units, middle left; three units, top left; 

 four units, right. 



three middle classes of the diagram. With six size-characters, 

 the extreme size of a grandparent would reappear no oftener 

 than once in four thousand times, while with a dozen such 

 independent characters it would recur only once in some 

 seventeen million times. It would be remarkable if under 

 such conditions the extreme size were ever recovered from 

 an ordinary cross. 



