CUMULATIVE EFFECTS OF GENES 



GENOTYPES 



DISTRIBUTION OF PHENOTYPES 



Fig. 15. — Diagram showing the relations between the genotypes and the frequency 

 distribution of phenotypes where two genes of equal and additive effect are varying 

 independently of one another and two allelomorphs of each gene are equally 

 common. Dominance is assmned to be absent, so that the phenotypic expression is 

 proportional to the number of capital letters in the genotype. Five phenotypic classes 

 will be produced with two genes of equal effect, seven phenotypic classes with 

 three genes, nine with four, and so on. As the number of classes increases, and as 

 non-heritable influences exert their effect, the distribution of phenotypes approximates 

 more closely to a continuous curve. 



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