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| works to bring a new, favorable mutation or allele to a higher frequency – this type of selection is at work when new adaptations evolve |
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| opposite of positive selection – allele is selected against – will eventually be lost in the population |
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Definition
-proposes that most mutations in DNA or amino acid replacements between species are functionally neutral or nearly neutral and fixed by random genetic drift
-The assumption of neutrality offers a baseline expectation of how DNA should change over time when natural selection is absent |
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– foundation is neutral evolution – change in the frequencies of neutral alleles overtime due to drift
-determine the rate at which a protein diverges and can use this as a molecular clock → such as the rate of divergence amongst the globin protein |
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| The rate of amino acid changes in three proteins |
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– each line represents the rate at which each protein has changed over time
-the rate at which these are accumulating amino acid substitutions is different (diverging at different rates)
-all equally important (importance doesn't depend on divergent rates)
-the more structural constraint on the protein - the less quickly it will change (and vice versa) |
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neutral - changes don't affect amino acid
-rate of nucleotide substitution is higher since it doesn't affect the proteins
i.e. introns (around 50% divergence in mammals) |
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| not neutral - change affects amino acid - smaller rate of change |
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