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increased mutation rates, and other features typical of their small population sizes. This included the loss of several transcriptional fidelity factors. Traverse and Ochman’s results showed that the transcriptional error rates between E. coli and the two endosymbionts were nearly equal even though their population sizes were very different. Their initial prediction was that the endosymbionts would have higher transcription error rates as they were subject to a large amount of genetic drift. This would mean that they would therefore sustain more deleterious mutations. However, neither
Buchnera aphidicola and Carsonella ruddii had elevated transcription error rates.
82:. The population keeps fixing these advantageous traits over time, pushing the population towards the genetic perfection associated with the environment. This increasing perfection causes mutations to have a higher chance of being deleterious. Individuals with a high mutation rate now increasingly decrease population fitness, and selection causes the mutation rate to decrease again. At the same time, new advantageous alleles have a diminishing positive effect on fitness. At a certain point, natural selection, mutation rate and random genetic drift reach a balance. This is called the drift-barrier.
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in 2010. It suggests that the perfection of the performance of a trait, in a specific environment, by natural selection will hit a hypothetical barrier. The closer a trait comes to perfection, the smaller the fitness advantages become. Once this barrier is reached, the effects of further beneficial
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Traverse and Ochman showed a striking exception to the drift-barrier hypothesis. In 2016, they measured transcriptional error rates in
Escherichia coli as well as two endosymbiotic prokaryotes, Buchnera aphidicola and Carsonella ruddii. The endosymbionts had dramatically reduced genome sizes,
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mutations are unlikely to be large enough to overcome the power of random genetic drift. Selection generally favors lower mutation rates due to the associated load of deleterious mutations that come with a high mutation rate.
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to environmental changes. Such populations have a bigger genetic pool, and therefore a bigger chance of containing an advantageous functional trait for this new environment. These advantageous functional traits get
65:. The balance between the influence of natural selection and genetic drift on the population mutation rate is mainly determined by the population size. Large populations are predicted to generally have lower
49:. When the environment in which the population lives changes, some of these traits turn out to be more advantageous for this new situation than others. Through
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Lynch, Michael; Ackerman, Matthew S.; Gout, Jean-Francois; Long, Hongan; Sung, Way; Thomas, W. Kelley; Foster, Patricia L. (November 2016).
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Left: Random genetic drift (blue arrows) impede selection (red arrows) towards 'genetic perfection'. Right: Simulation of mutation rates.
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470:"Conserved rates and patterns of transcription errors across bacterial growth states and lifestyles"
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than smaller populations. Populations containing individuals with high mutation rates are more
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Sung, Way; Ackerman, Matthew S.; Miller, Samuel F.; Doak, Thomas G.; Lynch, Michael (2012).
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375:, General Plant Pathology, The American Phytopathological Society, pp. 59–86,
285:"Sandwalk: Learning about modern evolutionary theory: the drift-barrier hypothesis"
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Proceedings of the
National Academy of Sciences of the United States of America
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Population
Biology of Plant Pathogens: Genetics, Ecology, and Evolution
230:"Genetic drift, selection and the evolution of the mutation rate"
411:"A constant rate of spontaneous mutation in DNA-based microbes"
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Milgroom, Michael G. (2017-08-02), Michael, G. Milgroom (ed.),
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McCandlish, David M.; Plotkin, Joshua B. (2016-03-22).
163:"Drift-barrier hypothesis and mutation-rate evolution"
468:Traverse, Charles C.; Ochman, Howard (2016-03-22).
57:, the traits with a negative effect on population
474:Proceedings of the National Academy of Sciences
415:Proceedings of the National Academy of Sciences
314:Proceedings of the National Academy of Sciences
369:"CHAPTER 4: Mutation and Random Genetic Drift"
310:"Transcriptional errors and the drift barrier"
41:Every population contains a certain amount of
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109:"Evolution of the mutation rate"
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409:Drake, J. W. (1991-08-15).
283:Moran, Larry (2016-12-01).
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381:10.1094/9780890544525.004
125:10.1016/j.tig.2010.05.003
18:drift-barrier hypothesis
487:10.1073/pnas.1525329113
428:10.1073/pnas.88.16.7160
327:10.1073/pnas.1601785113
234:Nature Reviews Genetics
180:10.1073/pnas.1216223109
45:, coding for different
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80:directional selection
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246:10.1038/nrg.2016.104
538:Theoretical ecology
173:(45): 18488–18492.
61:disappear from the
107:Lynch, M. (2010).
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480:(12): 3311–3316.
421:(16): 7160–7164.
390:978-0-89054-452-5
320:(12): 3136–3138.
51:natural selection
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43:genetic variation
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294:2021-09-23
95:References
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336:0027-8424
254:1471-0064
189:0027-8424
71:adaptable
63:gene pool
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354:26966235
289:Sandwalk
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215:23077252
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