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Antagonistic epistasis

Epistasis is the degree of overall fitness provided by a new mutation to the genome. Kryazhimskiy et al. (2011) summarize in clear terms the results of two papers published in the same issue of Science. For a population of microbes mutating inside a controlled and isolated laboratory environment, the rate of fitness diminishes with time because more and more mutations are antagonistic: individually, a mutation brings more fitness to the genome but together with other mutations, the fitness decreases. These results are in accord with a recent theory of mutation.