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# Maintaining Genetic Variation (Population Equilibrium) Populations have TWO competing factors: Remaining stable (not evolving) vs Changing (evolving)

## Presentation on theme: "Maintaining Genetic Variation (Population Equilibrium) Populations have TWO competing factors: Remaining stable (not evolving) vs Changing (evolving)"— Presentation transcript:

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

Hardy Weinberg Equilibrium “In the absence of outside forces, the frequency of each allele in a population will NOT change as generations pass. ”

Hardy-Weinberg Principles The following factors will help to keep population gene pools stable, that is, these factors will prevent evolution from occurring: 1.No Selection (natural, artificial or sexual) 2.No Mutation (or any other gene changes) 3.No Gene Flow (no migration) 4.Random mating (no mate selection) 5.Large population size (keeps new genes low in number)

Recall that…. The driving forces or mechanisms of evolution are exactly the opposite, that is, the following factors will cause evolution (changes in gene frequencies) to occur: 1.Selection (natural, artificial or sexual) 2.Mutation (or any other gene changes) 3.Gene Flow (migration) 4.Non-Random mating (mate selection) 5.Small population size (new genes will have a greater chance to be passed on)

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. p 2 + 2 pq + q 2 = 1 Where p = the frequency of the dominant allele Where q = the frequency of the recessive allele Where pq = the frequency of heterozygotes

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: A (0.93)a (0.07) A (0.93) AA 0.8649 Aa 0.0651 a (0.07) Aa 0.0651 aa 0.0049

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

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