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Natural Selection

Natural Selection. Natural Selection is based on reproductive success (fitness)…. Absolute fitness (think how hard that is to measure for genotypes) Relative fitness Relative fitness depends on other genotypes. Fitness values may change when the environment changes.

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Natural Selection

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  1. Natural Selection

  2. Natural Selection is based on reproductive success (fitness)… • Absolute fitness (think how hard that is to measure for genotypes) • Relative fitness • Relative fitness depends on other genotypes

  3. Fitness values may change when the environment changes

  4. Normal and sickle hemoglobin alleles AA and AS SS Which genotype has the highest fitness in our environment?

  5. Malaria parasites destroy RBC’s AA AS Which genotype has the highest fitness in malaria environment?

  6. To predict what will happen in this environment, need to know relative fitness: • When malaria is present: • Relative fitness AS = 1.00 • Relative fitness AA = 0.91—reduced by malaria • Relative fitness SS = 0.11—reduced by sickle-cell anemia • What IF the environment changes? • What will happen to relative fitness if malaria becomes more virulent (or more resistant to available treatments)? • What will happen to relative fitness if malaria is eradicated?

  7. Another hemoglobin allele you might not have heard of, “C” Hemoglobin c allele frequency indicated by red

  8. What happens to fitness if C allele is present? (AC, SC, and CC genotypes) • Assignment

  9. Selection pressure: Intense vs. weakDepends on fitness differentials

  10. “Winning” with Natural Selection Strategy 1: Survive long enough to reproduce Provide well for your offspring Straight “Natural Selection” “Live Long and Prosper”

  11. Medium ground finches on Daphne Major Rosemary and Peter Grant Field work since 1973 (half of each year)

  12. A variable population

  13. Variation is heritable

  14. Drought:Seeds rarerSeeds harder

  15. Many medium ground finches died!

  16. Avg. beak depth increased Note: the babies born later had bigger beaks… (due to differential reproduction in their parents’ generation)

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