Metabolic Polymorphisms in Mammals and Their Bearing on Problems of Biochemical Genetics

Abstract

Numerous genetically controlled chemical differences have recently been described in mammals. The commonest situation seems to be that in which allelic genes control the formation of closely related but distinct proteins, 2 of which are present in heterozygotes. The proteins can differ by as little as single amino-acid substitutions in each molecule or part of a molecule. Blood groups in heterozygotes may be "hybrid" and differ from those in homozygotes, but there is no evidence that this occurs in case of protein products of allelic genes. In another group of polymorphisms, different amounts of the same product (usually enzymes) are present in the several phenotypes. Some of the polymorphisms are known to be maintained by heterozygous advantage. There is suggestive evidence for unequal fitness of the several phenotypes in other cases, but the genetic mechanisms controlling the polymorphisms are not yet known.