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Maintaining Genetic Variation (Population Equilibrium )

Maintaining Genetic Variation (Population Equilibrium ). Populations have TWO competing factors: Remaining stable (not evolving) or Changing (evolving). Hardy Weinberg Equilibrium. it states that…..

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Maintaining Genetic Variation (Population Equilibrium )

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  1. Maintaining Genetic Variation (Population Equilibrium ) Populations have TWO competing factors: Remaining stable (not evolving) or Changing (evolving)

  2. Hardy Weinberg Equilibrium it states that….. “ In the absence of outside forces, the frequency of each allele in a population will NOT change as generations pass. ” http://www.pbs.org/wgbh/evolution/library/11/1/quicktime/e_m_2.html (school activity with the gene pool shown – 5 min)

  3. Hardy-Weinberg Principle The following factors will help to keep population gene pools stable, that is, these factors will prevent evolution from occurring: • No Selection (natural or artificial) • No Mutation (or any other gene changes) • No Gene Flow (no migration) • Random mating (no mate selection) • Large population size (keeps new genes that may arise, low in number)

  4. Recall that…. The driving forces (mechanisms) of evolution are exactly the opposite, that is, the following factors will cause evolution (changes in gene frequencies) to occur: • Selection (natural, artificial or sexual) • Mutation (or any other gene changes) • Gene Flow (migration) • Non-Random mating (mate selection) • Small population size (new genes will have a greater chance to be passed on)

  5. Hardy Weinberg Equation • A mathematical equation that helps evolutionary biologists figure out if a population gene pool has remained stable or if it has evolved. p2 + 2 pq + q2 = 1 • Where p = the frequency of the dominant allele • Where q = the frequency of the recessive allele • Where pq = the frequency of heterozygotes

  6. Using the Hardy-Weinberg Equation If the frequency of allele “a” is 7%, Find the frequency of: allele “A”, as well as genotypes AA, Aa, and aa. A: 100% - 7% = 93% (1.0 – 0.07 = 0.93) AA, Aa and aa:

  7. Teddy Graham Lab Watch the frequency of Happy vs. Sad Bears change before your eyes!!

  8. Table 1: Phenotypic Frequencies (round % to 1 decimal place) Use this number to start the punnett square

  9. Punnet Squares – Generation 1 (round to 3 decimal places max) Start Here Square root of 0.70 They all add up to 1.0

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