Directional selection

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Modes of selection
Directional selection increase in dark
phenotype as pollution increases
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Directional selection increase in size of
horses as forests gave way to prairie
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Diversifying selection
(Example of Crypsis too)
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Aposematic coloration Would you pick these up?
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Batesian mimicry tasty mimic converges on
distasteful model
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Mullerian mimicry distasteful models Look like
each other
Heliconius butterflies
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Crypsis phenotype hides animal
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Summary of Evolutionary Mechanisms
Process Definition Effect on variation Effect on fitness
Selection Certain alleles favored maintenance, increase or reduction Produces adaptation
Genetic drift Random changes in allele freq. Important in small populations Tends to reduce due to loss or fixation Usually reduces
Gene flow Movement of alleles between populations. Reduces differences May increase due to introduction, may decrease by removing May increase by introducing high fitness alleles, may decrease if a low fitness allele
Mutation Production of new alleles Increases by introducing new alleles Random, most lower fitness