A model of compensatory molecular evolution involving multiple sites in RNA molecules.

Consider two sites under compensatory fitness interaction, such as a Watson-Crick base pair in an RNA helix or two interacting residues in a protein. A mutation at any one of these two sites may reduce the fitness of an individual. However, fitness may be restored by the occurrence of a second mutation at the other site.

Models of compensatory molecular evolution: effects of back mutation.

Compensatory mutations are individually deleterious but appropriate combinations of mutants are harmless. For several models of compensatory molecular evolution, we consider the effects of back mutation. It is shown that the effects of back mutation on the rate of compensatory molecular evolution are weak.

Compensatory evolution in diploid populations.

Compensatory mutations are individually deleterious but harmless in appropriate combinations either at more than two sites within a gene or on separate genes. Considering that dominance effects of selection and heterodimer formation of gene products may affect the rate of compensatory evolution, we investigate compensatory neutral mutation models for diploid populations. Our theoretical analysis on the average time until fixation of compensatory mutations shows that these factors play an important role in reducing the fixation time of compensatory mutations if mutation rates are not low.