Polymorphism and the subunit structure of enzymes: a contribution to the neutralist-selectionist controversy.

The occurrence of polymorphism in a series of 87 different loci coding for enzyme structure in human populations has been related to the size and the number of subunits in the corresponding enzymes. Polymorphic and nonpolymorphic enzymes did not differ on average in subunit size. However, multimeric enzymes showed a significantly lower incidence of polymorphism than didmonomeric enzymes. A particularly low incidence of polymorphism was noted among multimeric enzymes in which interlocus molecular hybrids occur. The findings are discussed in terms of the "neutralist" and "selectionist" hypotheses of polymorphism.