196 



GENETICS AND EUGENICS 



From Table 28 it will be seen that when three like factors 

 are concerned, fifty to one hundred individuals must be pro- 

 duced to insure the recovery of the parental condition in F2; 



with 4 like factors, 200-300 individuals must be produced ; 

 " 5 " " over 1000 " « " « ; and 



« 6 " " " 4000 " " « " 



The foregoing calculations are based on the assumption 

 that each of the several hypothetical factors involved has an 

 equal influence in determining the general result and that all 



TABLE 28 



Theoretical Factorial Composition of a Population Produced by a 



Cross Involving more than a Single Mendelian Factor, 



Dominance being wanting 



are mutually independent (not linked). If, however, one or 

 more of the factors had greater influence than the others, the 

 apparent blending would be less perfect and a "tendency 

 toward segregation" or "imperfect segregation" would re- 

 sult. It is probable that this is the correct explanation of 

 what at one time was called "a type of inheritance inter- 

 mediate between Mendelian and blending." Also if certain 

 of the multiple factors were linked (borne in the same chro- 

 mosome), this would result in a tendency of the factors to 

 segregate in groups as originally introduced into the cross, 

 although crossing-over might lead to the production of 

 transitional types, any of which would "breed true" as soon 

 as all factors involved became homozygous. 



