Genetic redundancy

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Genetic redundancy is seen when a mutation in a gene has little effect on an organism's phenotype because its lost activity is compensated for by the function of a different gene or genetic pathway. In classical Mendelian genetics experiments this manifests as a form of epistasis where the vast majority of the progeny of a dihybrid cross have normal or near normal phenotypes and only the double homozygous recessive genotype shows a severe mutant phenotype.

Genetic redundancy is not associated with gene duplication and redundant genes do not mutate faster than essential genes. However, multiple individually harmful mutations can accumulate on a redundant gene, leading eventually to a beneficial gene that would not otherwise be accessible. One example of this is the inferred evolution of hemoglobin from myoglobin in vertebrate animals.