NE

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