Neo-Mendelism 53 



grained and white-grained corn he obtained all red in 

 the F ? generation. This would suggest that the F 2 

 generation would show 3 red to i white; but it showed 

 9 reds to 7 whites, which did not suggest Mendelian 

 inheritance. It* is in accord with MendePs law, how- 

 ever, if we consider that two complementary factors are 

 necessary to produce the red character, and that each of 

 these factors is inherited separately. Such a situation 

 would give a dihybrid ratio, as indicated in fig. 9. It 

 will be seen that out of 16 progeny 9 will be red, for they 

 alone contain the complementary factors; the other 7 will 

 be white. The situation is thus explained by the dihybrid 

 ratio, but although only one character is involved that 

 character depends upon two complementary factors. 



Another situation is worth noting. No. 6 of the 

 diagram is white because it contains only one of the 

 necessary factors; no. n is white for the same reason, 

 but its germinal constitution is just the opposite. What 

 would happen if these two are crossed ? There is only 

 one possibility, since each is a homozygote producing only 

 one kind of gamete. The result would be red, and 

 thus a cross between two whites would produce only 

 reds. What would happen from crossing nos. 6 and 15, 

 the former being a homozygote and the latter a hetero- 

 zygote ? It is obvious that the resulting progeny would 

 be one-half white and one-half red, although both parents 

 are white. The same result would be secured in cross- 

 ing nos. ii and 14. A cross between nos. 14 and 15, 

 both of which are heterozygotes, would result in 3 

 whites and i red, the ordinary 3 : i ratio. These illus- 

 trations show how differently the same phenotype may 

 behave in inheritance. In each case two whites were 



