No. 531] GENOTYPE CONCEPTION OF HEREDITY 149 



mined in this regard by Mendelian analysis is the nuwhrr 

 of differing points between the two gametes forming a 

 heterozygote. Such differences may be termed " geno- 

 differences." The well-known facts, that a " character" 

 may be dominant in some hybrids but recessive in others, 

 and that segregation in different cases may be very dif- 

 ferent, indicate that ' 'characters" are complicated reac- 

 tions. The famous case of Bateson's fowl-hybrids as to 

 the form of comb may here be quoted as an example : In 

 Walnut comb X Rose comb the latter is recessive, in 

 Single comb X Rose comb it is dominant, and in both 

 casesthe segregation gives tlireedominants: one recessive. 

 Xmv Bateson has shown that "Walnut" is a compound 

 of Rose- and Pea-comb. Homozygotic Walnut differs 

 from homozygotic Rose only in one point, as does Rose 

 compared with Single. But Walnut-gametes differ from 

 Single-gametes in two points; hence Walnut X Single, 

 with Walnut as dominant, segregates in Walnut, Rose, 

 Pea and Single in the proportions 9:3:3:1. Even with 

 tli is analysis it is as yet not possible to decide whether 

 Single or Walnut is the form of comb for the realization 

 of which the greater number of positive factors are re- 

 quired. Suggesting — what seems to be the most prob- 

 able assumption— that Walnut is the most geno-compli- 

 cated case, Single may even be an expression for a 

 multitude of genes in the fowl-constitution. The rela- 

 tivity of the analysis by segregation must in all such 

 cases be remembered, and it is quite erroneous to think 

 that dominance indicates the positivity of the "unit- 

 factor" in question: So "Horns" are in Wood's cases 

 dominant in male sheep but recessive in female sheep. 

 And as to analogs with chemical reactions it must be 

 kept in mind that a characteristic reaction may be the 

 consequence of lack of any substance as well as de- 

 pendent upon the presence of any special compound in 

 the solution in question. 



The elaborate work of Mendelians of recent years has 

 shown very complicated segregations, and the most spe- 

 cialized segregation is almost the most specialized analy- 



