Population Genetics Notes

# Population Genetics Notes - 7.03 Genetics Lectures 29-30 TA...

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7.03 Genetics – Lectures 29-30 TA: Yun Song 912-484-2511 | [email protected] Main Concepts Population Genetics: - p: f(A) p = f(AA) + ½ f(Aa) - q: f(a) q = f(aa) + ½ f(Aa) - Total allele frequencies: p + q = 1 - Total genotype frequencies: f(AA) + f(Aa) + f(aa) = 1 Hardy-Weinberg Equilibrium: - Assumptions : random mating, no new mutations, no selection, no migration - Result : allele frequencies stay constant from generation to generation - f(AA) = p 2 f(Aa) = 2pq f(aa) = q 2 - Prove that allele frequencies remain constant Deviation from Hardy-Weinberg Equilibrium: - Assortative mating: preferential mating between like (positive) or unlike (negative) individuals - Selection - New mutations arise - Genetic drift / founder effect: in small populations, chance fluctuations in the alleles that are transmitted can cause changes in allele frequency - Migration of individuals between different populations o In H-W equilibrium after one generation if there is random mating o Out of equilibrium if assortative mating occurs Effect of Mutations and Selection: μ = mutation rate (probability of a mutation per generation) s = selective disadvantage w = fitness = 1-s - Fitness o w = p 2 w AA + 2pqw Aa + q 2 w aa = pw A + qw a o w A = pw AA + qw Aa o w a = qw aa + pw Aa - Selection against rare recessive allele Genotype Frequency After Selection Δ Frequency AA p 2 p 2 0 Aa 2pq 2pq 0 aa q 2 q 2 (1-s) -sq 2 At equilibrium: Δ q sel + Δ q mut = 0 -sq 2 + μ = 0 q eq = sqrt(μ/s)

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7.03 Genetics – Lectures 29-30 TA: Yun Song 912-484-2511 | [email protected] - Selection against rare dominant allele
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Population Genetics Notes - 7.03 Genetics Lectures 29-30 TA...

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