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Chapter 5 review

• The spectrum of relative fitness for genotypes containing mutations expresses the frequencies of mutations with a range of fitness effects. Mutations that are strongly deleterious or lethal will be purged by natural selection, while strongly advantageous mutations will be fixed by natural selection. Mutations with smaller effects may be neutral or nearly neutral and therefore be subject or stochastic fixation or loss due to genetic drift.

• New mutations may be lost simply by Mendelian segregation since there is a

chance that a given single allele will not be transmitted to k progeny. Neutral mutations are eventually lost while the chance of a new selectively favored mutation escaping loss (becoming fixed) is approximately twice its selective advantage, under the assumption that the population size is very large. New selectively neutral mutations are initially at a frequency of

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