Measuring Evolution of Populations

• Populations and Gene Pools
  • Concepts
  • A population is a localized group of interbreeding individuals
  • Gene pool is a collection of alleles in the population
  • Allele frequency is how common that allele in the population
• Evolution of Populations
  • Evolution
  • Change in allele frequencies in a population
  • Non-evolving population
  • Remove all agents of evolutionary change
    • Very large population size
    • No genetic drift
    • No migration
    • No gene flow
    • No mutation
    • No genetic change
    • Random mating
    • No sexual selection
    • No natural selection
    • Everybody is equally fit
• Hardy-Weinberg Equilibrium
  • Hypothetical, non-evolving population
  • Preserves allele frequencies
  • Serves as a model (null hypothesis)
  • Natural populations rarely in H-W equilibrium
  • Useful model to measure if forces are acting on a population
    • Measuring evolutionary change
• Hardy-Weinberg Theorem
  • Counting alleles
  • Assume 2 alleles
    • B,b
  • Frequency of dominant allele
    • Variable p
  • Frequency of recessive allele
    • Variable q
    • Frequencies must ad to 1
    • p+q=1
  • Counting individuals
  • Frequency of homozygous dominant
    • p*p=p^2
  • Frequency of homozygous recessive
    • q*q=q^2
  • Frequency of heterozygotes
    • (p*q)+(q*p)=pq
    • Frequency of all individuals must add up to 1
    • p^2+qp+q^2=1
• Application of H-W Principle
  • Sickle cell anemia
  • Inherit mutation in gene coding for hemoglobin
    • Oxygen-carrying blood protein
  • Low oxygen levels cause RBC to sickle
    • Breakdown of RBC
    • Clogging small blood vessels
    • Damage to organs
  • Often lethal
• Sickle Cell Frequency
  • High frequency of heterozygotes
  • 1 in 5 in Central Africans
  • Unusual for allele with severe detrimental effects in homo zygotes
    • 1 in 100
    • Usually die before reproductive age
• Heterozygote Advantage
  • In tropical Africa, where malaria is common
  • Homozygous dominant (normal)
    • Die or reduced reproduction from malaria
  • Homozygous recessive
    • Die or reduced reproduction from sickle cell anemia
  • Heterozygote carriers
    • Relatively free of both
    • Survive and reproduce more

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