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| In genetic terms, evolution is any change in the relative frequency of alleles in a population. |
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| Biologists have discovered that that there are two main sources of genetic variation: mutations and the genetic shuffling that results from sexual reproduction |
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| The number of phenotypes produced for a given trait depends on how many genes control the trait |
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| Natural selection of single gene traits can lead to changes in allele frequencies and thus to evolution |
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| Natural selection can affect the distributions of phenotypes in any three ways: directional selection, stabilizing selection, or disruptive selection |
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| In small populations, individuals that carry a particular allele may leave more descendants than other individuals, just by chance. Over time, a series of chance occurrences of this type can cause an allele to become common in a population |
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| Five conditions are required to maintain genetic equilibrium from generation to generation: There must be random mating; the population must be very large; and there can be no movement into or out of the population, no mutations, and no natural selection |
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| As new species evolve, populations become reproductively isolated from each other |
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