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Evolution in populations

Evolution in populations. Think Change over loooong periods of time. Gene pool: all the genes in a population. Not just the genes, but the variation of genes Allelic frequency; distribution of alleles. A population whose allelic frequency is not changing is in genetic equilibrium

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Evolution in populations

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  1. Evolution in populations Think Change over loooong periods of time

  2. Gene pool: all the genes in a population. • Not just the genes, but the variation of genes • Allelic frequency; distribution of alleles

  3. A population whose allelic frequency is not changing is in genetic equilibrium • Genes aren’t changing, allele frequency isn’t changing, species isn’t changing

  4. Evolution is a change in genetic equilibrium • Rephrase- • Evolution is a change in the allelic frequencies

  5. How do gene pools change? • Mutation • Genetic drift- small population becomes isolated, through chance or on purpose • Immigration or emigration-

  6. Bottleneck effect • Over-hunting • Fire • Flood • Earthquake Changes the gene pool due to chance

  7. Examples • 1. Species is hunted to near extinction • Northern elephant seals in California hunted to 20 individuals. • Now at 30,000, but there is no genetic variation

  8. How do gene pools change? • All populations have variation- inheritable traits controlled by alleles • Natural selection has the greatest affect on large gene pools over time- selecting for those traits that confer an advantage

  9. Three different types of natural selection that acts on variation • 1. Stabilizing • 2. Directional • 3. Disruptive

  10. Stabilizing • Selects against extremes in variation- favors the intermediary. • Example: small and large variations of a spider • Reduces variation 1

  11. Directional • Natural selection favors one extreme • Example: woodpeckers with longer beaks • Can lead to rapid evolution • 2

  12. Disruptive • Selects against the intermediate form- selects for the two opposite extremes. • Example: white, tan, brown limpets (a type of marine organism • &

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