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Evolution of Populations Chapter 11

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Genetic Variation Within Populations Variation and gene pools Gene pool all genes present in a population Allele Frequency the number of times an allele occurs in the gene pool, compared to other alleles

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Genetic Variation Within Populations In genetic terms, evolution is any change in the relative frequency of alleles in a population.

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Genetic Variation Within Populations Scientists now recognize two main sources of genetic variation Scientists now recognize two main sources of genetic variation Mutations Mutations Recombination Recombination

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Genetic Variation Within Populations Mutations Any change in a sequence of DNA Occurs Because: Problems with replication Exposure to radiation or chemicals

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Genetic Variation Within Populations Recombination Parents alleles rearrange when forming gametes The 23 pairs of chromosomes can produce 8.4 million different combinations!

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Genetic Variation Within Populations Crossing Over Occurs during meiosis Further increases genetic variation

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Natural Selection In Populations Normal distribution Normal distribution Highest frequency in middle and lowest at the extremes Highest frequency in middle and lowest at the extremes Also representative for allele freqencies Also representative for allele freqencies

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Natural Selection In Populations Microevolution Observable changes in allelic frequencies Occurs in a single population 3 ways Directional Stabilizing Disruptive

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Natural Selection In Populations Directional Selection Directional Selection Shift in phenotype to one extreme Shift in phenotype to one extreme Mean also shifts Mean also shifts

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Natural Selection In Populations Stabilizing Selection Norm is selected for and becomes more common Ex. Gall Fly and Goldenrod

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Natural Selection In Populations Disruptive Selection Disruptive Selection Selection for the extremes Selection for the extremes Ex. Peppered moths Ex. Peppered moths

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Natural Selection In Populations Single-gene and polygenic traits Widows peak is a single gene trait a single gene with two alleles Polygenic Traits are controlled by two or more genes This means that a polygenic trait can have many possible genotypes ant thus phenotypes.

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16-2 Evolution as Genetic Change Natural Selection on Single-Gene Traits

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Other Mechanisms of Evolution Gene Flow Gene Flow Some animals move once they are able Some animals move once they are able When the move into new population, their alleles become part of gene pool When the move into new population, their alleles become part of gene pool Occurs with movement between populations Occurs with movement between populations Increases variation Increases variation If less movement, the more different two species become If less movement, the more different two species become

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Other Mechanisms of Evolution Genetic Drift Random change in allele frequency Bottleneck Effect Founder effect when allele frequencies change because of migration

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Other Mechanisms of Evolution Sexual Selection Females the important factor in reproduction This makes females picky Intrasexual selection Intersexual selection

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Hardy-Weinberg Equilibrium Evolution vs. Genetic Equilibrium Hardy-Weinberg principle genotype frequencies will stay constant unless some factor changes the frequency Genetic Equilibrium when allele frequencies remain constant

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Hardy-Weinberg Equilibrium Five Conditions to Maintain Equilibrium Random Mating Large Population No Movement into or out of the population No Mutations No Natural Selection

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Hardy-Weinberg Equilibrium Biologists can use an equation for comparison purposes Biologists can use an equation for comparison purposes p2 + 2pq + q 2 = 1 p = dominant alleles q = recessive alleles

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Hardy-Weinberg Equilibrium Five factors leading to evolution Five factors leading to evolution Genetic drift Genetic drift Gene flow Gene flow Sexual selection Sexual selection Natural selection Natural selection Mutations Mutations

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Speciation Through Isolation Reproductive Isolation members of populations can no longer mate Mules or Hinnies Speciation - when two species come from one existing species

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Speciation Through Isolation Behavioral Isolation Two populations will not breed because of differences in courtship Fireflies

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Speciation Through Isolation Geographical Isolation Rivers, mountains, or bodies of water separate two populations Snapping Shrimp and placental vs. marsupial mammals

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Speciation Through Isolation Temporal Isolation Different species mate at different times Times of day Times of year Trees and plants

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Patterns in Evolution Convergent Evolution evolution towards similar characteristics in unrelated species Convergent Evolution evolution towards similar characteristics in unrelated species Analogous structures Analogous structures Bird and bat wings Bird and bat wings

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Patterns in Evolution Divergent Evolution closely related species in different directions Results from adapting to different environments Kit and Red Fox

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Patterns in Evolution Coevolution two or more species evolve in response to changes in each other Coevolution two or more species evolve in response to changes in each other Benefit to both species Benefit to both species Plants and bees Plants and bees

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Patterns in Evolution Coevolution can also drive predator-prey relationships Cheetahs and gazelles

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Patterns in Evolution Extinctions species are eliminated Extinctions species are eliminated Background extinctions occur continously, but at very low rates Background extinctions occur continously, but at very low rates Mass extinctions rare, more intense, involve many species Mass extinctions rare, more intense, involve many species

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Patterns in Evolution Punctuated equilibrium bursts of evolutionary activity followed by periods of inactivity Punctuated equilibrium bursts of evolutionary activity followed by periods of inactivity Adaptive radiation diversification of multiple species from one ancestral species Adaptive radiation diversification of multiple species from one ancestral species Mammals Mammals