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chapter 17 edited - Processes of Evolution Chapter 17 17.1...

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Processes of Evolution Chapter 17
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17.1 Populations Evolve Population Individuals of the same species in the same area Generally the same number and kinds of genes for the same traits Gene pool All the genes of a population
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Variation in Alleles Individuals who inherit different combinations of alleles vary in details of one or more traits Polymorphism: Several alleles in a population Mutations are the original source of new alleles Lethal mutations result in death Neutral mutations neither help nor hurt
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Phenotypic Variation in Populations
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Microevolution Changes in allele frequencies of a population Mutation Natural selection Genetic drift Gene flow
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17.2 When Is A Population Not Evolving? Genetic equilibrium A state in which a population is not evolving Never occurs in nature Deviations from theoretical genetic equilibrium are used to study how a population is evolving
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Hardy-Weinberg Equilibrium Equation If frequency of alleles in a population changes, the population is evolving p + q = 1.0 p 2 + 2 pq + q 2 = 1.0 p and q = frequencies of alleles A and a 2 pq = carrier frequency
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Is This Population Evolving?
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17.3 Natural Selection Natural selection Differential survival and reproduction among individuals of a population that show variations in details of their shared traits ( alleles ) Allele frequencies Maintained by stabilizing selection Shifted by directional or disruptive selection
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Modes of Natural Selection
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17.4 Directional Selection Shifts range of variation in traits in one direction Individuals at one end of the range are favored; those at the other end are not Examples: Peppered moth, pocket mice (predation) Antibiotic resistance
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Directional Selection
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Peppered Moth
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Pocket Mice
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17.5 Selection For or Against Extreme Phenotypes Stabilizing Selection Works against both extremes in the range of phenotypic variation Favors intermediate forms Disruptive selection Favors forms at extremes of the range
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Stabilizing and Disruptive Selection
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Fig. 17.8a, p.272
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Fig. 17.8a, p.272
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