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The Evolution of Populations

Pops. The Evolution of Populations. Groupings. Species Pops of orgs that may interbreed to produce fertile offspring Population Local group of orgs of one species Evolution = change in the genetic makeup (allele frequencies) of a population. Hardy-Weinberg Conditions.

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The Evolution of Populations

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  1. Pops The Evolution of Populations

  2. Groupings • Species • Pops of orgs that may interbreed to produce fertile offspring • Population • Local group of orgs of one species • Evolution = change in the genetic makeup (allele frequencies) of a population

  3. Hardy-Weinberg Conditions • Hypothetical conditions that must exist in a population for no evolution to occur

  4. Population Characteristics Hinder Evolution (Hardy-Weinberg Conditions) Infinitely Large Random Mating Equal Survival Isolation No mutations Help Evolution (Natural Conditions) Small  Genetic Drift Natural Selection Natural Selection Gene Flow Mutations POPULATION SIZE MATE SELECTION VARIATION OF ADAPTIVENESS INTERACTION W/ OTHER POPS DNA CHANGES

  5. Genetic Drift • Random fluctuations in allele frequencies • Example: • 2 red, 2 blue orgs seek shelter • 50% survive. All are red • Blues eliminated by chance (17%) • 4 red, 4 blue head for shelter • 50% survive. All are red • Blues eliminated by chance (1.4%)

  6. Genetic Drift • Bottleneck Effect • Catastrophe cuts pop size • Decreased variety of traits • Altered allele frequencies • Genetic drift more likely

  7. Genetic Drift • Founder Effect • Small group emigrates to new habitat 

  8. Gene Flow • Introduction of new traits through immigration • May be beneficial or insignificant • New traits  altered trait frequencies 

  9. Quantifying Evolution Gene Pool • entire set of alleles present in the population Evolution • change in frequency of alleles in the population p = frequency of one allele (usu. dom.) q = frequency of another allele (usu. Rec.) p + q = 1

  10. Quantifying Evolution • p2 = frequency of homozygous dominants • q2 = frequency of homozygous recessives • 2pq = frequency of heterozygotes p + q = 1 p2+ 2pq + q2 = 1

  11. Quantifying Evolution Symbolized as “2pq” Symbolized as “p2” Symbolized as “q2” Symbolized as “p” Symbolized as “q”

  12. Hardy-Weinberg Probs • In Drosophila, the allele for normal wings is dominant over the allele for vestigial wings. In a pop of 1000, 490 have vestigial wings. How many individuals would you expect to be homozygous dominant? Heterozygous? • q2 = .49 • q = .7 • p = .3 • p2 = .09 • 2pq = .42

  13. Hardy-Weinberg Probs • In the US, 64% of people have free earlobes. What is the frequency of the dominant allele? • p2 + 2pq = .64 • q2 = .36 • q = .6 • p = .4

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