The role of balancing selection and overdominance in maintaining allozyme polymorphism.

Three approaches to the estimation of the role of balancing selection in maintaining allozyme polymorphism are considered: 1) Analysis of the stationary distributions of allelic frequencies in a native subdivided population; 2) Comparison of the genotypic distributions at the early and late developmental stages in successive generations of the same population; 3) Analysis of the 'joint' variability of monogenic and polygenic traits. The conclusion is drawn that allozyme polymorphism must not be regarded as a transient phase of molecular evolution but as its stationary phase. The mechanisms responsible for supporting such stability are discussed.