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Drift-barrier hypothesis and mutation-rate evolution
- Sung, Way, Ackerman, Matthew S., Miller, Samuel F., Doak, Thomas G., Lynch, Michael
- Proceedings of the National Academy of Sciences of the United States of America 2012 v.109 no.45 pp. 18488-18492
- DNA, eukaryotic cells, genome, mutation, natural selection, population size, prokaryotic cells
- Mutation dictates the tempo and mode of evolution, and like all traits, the mutation rate is subject to evolutionary modification. Here, we report refined estimates of the mutation rate for a prokaryote with an exceptionally small genome and for a unicellular eukaryote with a large genome. Combined with prior results, these estimates provide the basis for a potentially unifying explanation for the wide range in mutation rates that exists among organisms. Natural selection appears to reduce the mutation rate of a species to a level that scales negatively with both the effective population size (N ₑ), which imposes a drift barrier to the evolution of molecular refinements, and the genomic content of coding DNA, which is proportional to the target size for deleterious mutations. As a consequence of an expansion in genome size, some microbial eukaryotes with large N ₑ appear to have evolved mutation rates that are lower than those known to occur in prokaryotes, but multicellular eukaryotes have experienced elevations in the genome-wide deleterious mutation rate because of substantial reductions in N ₑ.