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Mechanisms of Evolution

Mechanisms of Evolution. Concept 4: Analyzing the evolution of populations through Hardy-Weinberg (microevolution) Chapter 23 in Campbell, pg 155-158 in Holtzclaw. Goal: To analyze how populations change over time . The Evolution of Populations. You must know:

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Mechanisms of Evolution

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  1. Mechanisms of Evolution Concept 4: Analyzing the evolution of populations through Hardy-Weinberg (microevolution) Chapter 23 in Campbell, pg 155-158 in Holtzclaw

  2. Goal: To analyze how populations change over time

  3. The Evolution of Populations You must know: • How mutation and sexual reproduction each produce genetic variation • The conditions for Hardy-Weinberg Equilibrium • How to use the Hardy-Weinberg equation to calculate allelic frequencies, to test whether a population is evolving.

  4. Genetic Variation • Crossing Over • Independent Assortment • Fertilization Gene pool = a population’s genetic make-up

  5. Remember... Homozygous...(dominant)(recessive) Heterozygous...(dominant will “show”)

  6. Preservation of Genetic Variation • Diploidy – “hiding” recessive alleles • Heterozygote advantage • Ex) sickle cell anemia - malaria

  7. What alters allele frequencies? • Three major factors: • Natural Selection – causes adaptive evolution • Genetic Drift • Founder Effect • Bottleneck Effect • Gene Flow (Mutations also alter allele frequencies, but rare)

  8. Natural Selection – causes adaptive evolution • Relative Fitness • Fitness compared to other members of the population… (your contribution to the gene pool of the next generation!) • Three ways natural selection can work: • Directional selection • Disruptive selection • Stabilizing selection

  9. Try This! • In what sense is natural selection more “predictable” than genetic drift?

  10. Try This! • In what sense is natural selection more “predictable” than genetic drift? • Natural Selection: • Alters allele frequency in a nonrandom way • Tends to increase the frequency of alleles that increase an organism’s fitness and decrease the frequency of alleles that decrease an organism’s fitness • Genetic Drift: • Alters allele frequency by chance alone

  11. Introducing…The Hardy-Weinberg Principle! • Clarifies the factors that alter allele frequency • A non-evolving population is in Hardy-Weinberg equilibrium.

  12. Conditions for Hardy-Weinberg Equilibrium: • No mutations • Random mating • No natural selection • Extremely large population size (no genetic drift) • No gene flow

  13. The Hardy-Weinberg Formula p2 + 2pq + q2 = 1 where p + q = 1 See Handout...

  14. Try This! In a certain population of 1000 fruit flies, 910 have red eyes while the remainder have sepia eyes. • The sepia eye trait is recessive to red eyes. • How many individuals would you expect to be homozygous for red eye color? Hint: The first step is always to calculate q2! Start by determining the number of fruit flies that are homozygous recessive…

  15. Try This! • Answer:You should expect 490 to be homozygous dominant.Calculations:q2 for this population is 90/1000 = 0.09q = = 0.3p = 1 - q = 1 - 0.3 = 0.7The homozygous dominant frequency = p2 = (0.7)(0.7) = 0.49.Therefore, you can expect 49% of 1000, or 490 individuals, to be homozygous dominant.

  16. Now… Handout!

  17. The Evolution of Populations Do you know? How mutation and sexual reproduction each produce genetic variation The conditions for Hardy-Weinberg Equilibrium How to use the Hardy-Weinberg equation to calculate allelic frequencies, to test whether a population is evolving.

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