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Hardy Weinberg Theorem and Equilibrium

Hardy Weinberg Theorem and Equilibrium. IB Topic/Option D4 Campbell Text pages 447-449. HW theorem describes a non-evolving population. 1908

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Hardy Weinberg Theorem and Equilibrium

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  1. Hardy Weinberg Theorem and Equilibrium IB Topic/Option D4 Campbell Text pages 447-449

  2. HW theorem describes a non-evolving population • 1908 • The frequency of alleles and genotypes in a population remain constant over generations unless acted upon by agents other than Mendelian segregation and recombination of alleles • Meiosis and random fertilization has no effect on the overall gene pool of a population

  3. The Hardy Weinberg Equation • If a population is in genetic equilibrium, predictions can be made about genotypic, phenotypic, and allele frequencies • The equation can be used for more than 2 alleles, but we’ll keep it simple

  4. HW Equation • p2 + 2pq + q2 = 1 • p + q = 1 • the sum of both frequencies equals 1 (100%) • p = frequency of dominant allele • The probability of being homozygous dominant (RR) is p x p • q = frequency of recessive allele • The probability of being homozygous recessive (rr) is q x q • 2pq • The probability of having heterozygous genotype • Frequency of Rr plus rR • The dominant and recessive allele can come from either parent

  5. PRACTICE! • In a population with two alleles for a particular locus, B and b, the allele frequency of B is 0.7. What would be the frequency of heterozygotes if the population were in Hardy Weinberg equilibrium? • 0.42

  6. More Practice! • In a population in HW equilibrium, 16% of the individuals show the recessive trait. What is the frequency of the dominant allele in the population? • 0.6

  7. Do people actually use this equation? • Yes! • Population genetics and health science • Can be used to estimate the percentage of the human population that carries the allele for a particular inherited disease • PKU (See page 449)

  8. HW Theorem and Genetic Variation • Important conceptually and historically • Shows how Mendel’s theory of inheritance “plugs a hole” in Darwin’s theory of natural selection • Natural selection requires genetic variation • HW theorem explains how Mendelian inheritance preserves genetic variation from one generation to the next • Remember Punnett squares? (See page 448)

  9. Assumptions of the HW Theorem • In order for a population to be in HW equilibrium, 5 conditions must be met: • 1. Very large population • 2. No migration • 3. No net mutations • 4. Random mating • 5. No natural selection

  10. Therefore, … • We do not really expect a natural population to be in Hardy Weinberg equilibrium • Deviation from a stable gene pool and HW equilibrium usually results in evolution

  11. Animations and tutorial • http://science.nhmccd.edu/BioL/hwe.html

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