EVOLUTION OF GENETIC REDUNDANCY

Genetic redundancy means that two or more genes are performing the sam e function and that inactivation of one of these genes has little or n o effect on the biological phenotype. Redundancy seems to be widesprea d in genomes of higher organisms(1-9). Examples of apparently redundan t genes come from numerous studies of developmental biology(10-15), im munology(16,17), neurobiology(18,19) and the cell cycle(20,21). Yet th ere is a problem: genes encoding functional proteins must be under sel ection pressure, If a gene was truly redundant then it would not be pr otected against the accumulation of deleterious mutations. A widesprea d view is therefore that such redundancy cannot be evolutionarily stab le. Here we develop a simple genetic model to analyse selection pressu res acting on redundant genes. We present four cases that can explain why genetic redundancy is common, In three cases, redundancy is even e volutionarily stable. Our theory provides a framework for exploring th e evolution of genetic organization.