title: Is Pi a selectively balanced polymorphism?
abstract: A stable polymorphism of the Pi alleles M1, M2 and M3 close to their observed frequencies has been predicted, simply by relating fitness to the proportion of each genotype having alpha 1-antitrypsin (alpha 1-AT) levels greater than 100 mg/100 ml. By further specifying that the rare S and Z genotypes with low alpha 1-AT levels have enhanced fertility, equilibria of the M, S and Z alleles have also been predicted close to their observed frequencies; however, none of these latter equilibria is stable, mainly because the predicted fitness of the SS genotype is too great.
mesh_terms: D000483:Alleles; D005787:Gene Frequency; D005838:Genotype; D006801:Humans; D010641:Phenotype; D011110:Polymorphism, Genetic; D012641:Selection, Genetic; D000515:alpha 1-Antitrypsin / Q000235:genetics*
chemical_list: D000515:alpha 1-Antitrypsin