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Hardy-Weinberg Equilibrium�AP Topic 7.5

  • Learning Objectives
    • Describe the conditions under which allele and genotype frequencies will change in populations.
    • Explain the impact on the population if any of the conditions of Hardy Weinberg are not met.

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Population Genetics

  • studies how genetic variation shifts over time
    • evolution occurs when allele frequencies change over generations
    • driven by multiple factors:
      • natural selection, genetic drift, gene flow, and mutation

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Evolution is also driven by random occurrences

  • Evolution is not solely driven by natural selection
  • Random events can shape allele frequencies in a population
    • These events may be unrelated to an organism’s fitness

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The Genetic Basis of Body Color in the Peppered Moth

  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
  • Jump to Long image Description

The genetic basis of body color in the peppered moth. Light or dark body color in the peppered moth is determined by a gene with two alleles, D and d. Genotypes DD and Dd produce dark body color, and dd produces light body color. The D and d alleles are variants of a gene at a particular locus on a chromosome.

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Hardy-Weinberg Principle Explored in detail Topic 7.5

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Allele Frequencies

  • measure of alleles in a population

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Calculation of Hardy-Weinberg equilibrium from gamete frequencies. Notice that the results of the Punnett square match those shown in the figure.

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Hardy-Weinberg Equilibrium � - A Non-Evolving Population

  • Used as a model to measure evolutionary change
  • No evolution occurs if these five conditions are met
    • No mutations
    • No natural selection
    • No genetic drift (large population size)
    • No gene flow (no migration)
    • Random mating (no sexual selection)
  • If allele frequencies change over generations, evolution is occurring.

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This Photo by Unknown Author is licensed under CC BY-SA

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Why Hardy-Weinberg �Equilibrium & Formulas?

  • Conditions for a population or an allele to be in Hardy-Weinberg equilibrium
    • These processes, and/or models in applied contexts
    • These conditions are seldom met, but they provide a valuable null hypothesis
    • Allele frequencies in a population can be calculated from genotype frequencies
    • Changes in allele frequencies provide evidence for the occurrence of evolution in a population

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Observing Allele and �Genotype Frequencies

  • Small populations are more susceptible to random environmental impact than large populations
    • observations of large populations
    • observe the change in alleles over successive generations

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Hardy-Weinberg �Formulas

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Allele Frequencies

Genotypes

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Calculating Allele �Frequencies

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Calculating Genotype Frequencies

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Sample Problem using �Hardy-Weinberg Equilibrium

  • A research team is looking at a random-mating population of laboratory mice. Out of the 1000 individuals 180 mice have the recessive white fur color (aa). Calculate the allele and genotype frequencies.

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Sample Problem using �Hardy-Weinberg Equilibrium

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Sample Problem using �Hardy-Weinberg Equilibrium

  • A research team is looking at a random-mating population of laboratory mice. Out of the 1000 individuals 180 mice have the recessive white fur color (aa). Calculate the allele and genotype frequencies.

Continue by determining dominant allele frequency

p + 0.42 = 1

p = 1 – 0.42

p = 0.58

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Sample Problem using �Hardy-Weinberg Equilibrium

  • A research team is looking at a random-mating population of laboratory mice. Out of the 1000 individuals 180 mice have the recessive white fur color (aa). Calculate the allele and genotype frequencies.

Allele Frequencies Determined – move on to genotypes

q = 0.42

p = 0.58

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Sample Problem using �Hardy-Weinberg Equilibrium

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Sample Problem using �Hardy-Weinberg Equilibrium

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What are the applications�of the Hardy-Weinberg Equilibrium?

  • Predicting genetic variation in populations
    • creates estimates
    • shows shifts in alleles if equilibrium is not observed
  • Understanding evolutionary processes
  • Implications for conservation biology
    • supports research and identifying endangered species

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Summary Hardy-Weinberg Equilibrium (Topic 7.5)

  • a principle in population genetics that describes the genetic variation in a population that remains constant from one generation to the next in the absence of disturbing factors
  • provides a baseline for studying evolutionary processes
  • helps identify factors that may affect population genetics

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