Why are phenotypic mutation rates much higher than genotypic mutations rates?

The evolution of genotypic mutation rates has been investigated in numerous theoretical and experimental studies. Mutations, however, occur not only when copying DNA, but also when building the phenotype, especially when translating and transcribing DNA to RNA and protein. Here we study the effect of such phenotypic mutations. We find a maximum phenotypic mutation rate, u_max, that is compatible with maintaining a certain function of the organism. This may be called a phenotypic error threshold. In particular, we find a minimum phenotypic mutation rate, u_min, with the property that there is (nearly) no selection pressure to reduce the rate of phenotypic mutations below this value. If there is a cost for lowering the phenotypic mutation rate, then u_min is close to the optimum phenotypic mutation rate which maximizes the fitness of the organism. In our model, selection minimizes the rate of genotypic mutations as far as possible, but the rate of phenotypic mutations only to a certain value. Despite its simplicity, our model can explain part of the huge difference between genotypic and phenotypic mutation rates that is observed in nature. The relevant data are summarized.

Key Words: error threshold, evolution, mutation rate, transcritpion, translation

This article has been cited by other articles:

				N. Stoletzki and A. Eyre-Walker Synonymous Codon Usage in Escherichia coli: Selection for Translational Accuracy Mol. Biol. Evol., February 1, 2007; 24(2): 374 - 381. [Abstract] [Full Text] [PDF]

				C. O. Wilke and D. A. Drummond Population Genetics of Translational Robustness Genetics, May 1, 2006; 173(1): 473 - 481. [Abstract] [Full Text] [PDF]

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