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8.1 Natural Selection

8.1 Natural Selection. Pages 326-335. Selection. Selective pressures include: Diseases Climate Food Predators Mates. Hummingbirds. 300 species of hummingbirds Varying beak length. Normal distribution curve. Measuring a trait such as hummingbird beak length. Flower size.

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8.1 Natural Selection

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  1. 8.1 Natural Selection Pages 326-335

  2. Selection Selective pressures include: • Diseases • Climate • Food • Predators • Mates

  3. Hummingbirds • 300 species of hummingbirds • Varying beak length

  4. Normal distribution curve • Measuring a trait such as hummingbird beak length.

  5. Flower size • Flower length affects beak length

  6. Directional Selection • Selection that favours an increase or decrease in the value of a trait from the current population average

  7. Stabilizing Selection • The average phenotype in a population is favoured.

  8. Disruptive Selection • Favours individuals with variations at opposite extremes of trait

  9. Sexual Selection • Favouring any trait that improves the odds of reproductive success.

  10. Bright plumage • Males and females often appear and behave differently from each other male female

  11. Competition • Fighting for territory and mates

  12. Risk • Mating behaviours attract predators

  13. Tibet

  14. Mice

  15. Genetic drift • Small populations can experience random shifts in allele frequencies due to chance

  16. Bottlenecks Very small population sizes result in a loss of genetic diversity

  17. Founder Effect • Isolated few establish a new population

  18. The Hardy-Weinberg Principle • In large populations allele frequencies are expected to remain constant from generation to generation

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