10.22.07 - H-W Equib.

10.22.07 - H-W Equib. - Darren Rothberg Biol 105 Evolution...

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Darren Rothberg Biol 105 – Evolution 10.22.07 Hardy-Weinberg Equilibrium (No Evolution) (Genetic Equilibrium) Derived Independently in 1908 by: o Godfrey Hardy o Wilhelm Weinberg No change in: Allele frequencies between generations Genotype frequencies between generations An example of the calculation: o Phenylketonuria A metabolic disorder in which humans are missing an enzyme that breaks down phenylalanine which can cause mental retardation if it accumulates in blood Phenylketonuria is a recessive disorder only exhibited in the homozygous recessive condition Can use H-W theorem to predict the frequency of humans carrying the recessive allele, but not showing the disease (heterozygotes) o U.S. Population Only homozygotes carrying two copies of the recessive allele exhibit the disease – medical records show this is 1:10,000 births Thus, q 2 = 0.0001, and q = 0.01 (1% frequency) If q = 0.01, then p = 0.99 p 2 + 2pq + q 2 = 1 2pq = 2 * 0.99 * 0.01 = 0.0198 (1.98% frequency) a Conditions required for a population to be in Hardy-Weinberg Equilibrium: i No mutation Without mutation there can not be evolution or a new allele for natural selection to act upon ii Random mating XX = ¼ XY = ¼ + ¼ = ½ YY = ¼ Positive assortative mating mating with similar organisms (No change in allele frequency) Negative assortative mating mating with different organisms
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(All heterozygotes) iii Infinitely large population size No genetic drift iv No differential reproductive success No natural selection v No gene flow No immigration from another population with different allele frequencies b What processes can cause evolution i Mutation: creates new variation (only minor change in allele frequency) ii Genetic drift: alters allele frequencies randomly iii Selection (natural or sexual) causes adaptation iv Gene flow (immigration or emigration) changes allele frequencies in ways that can be non-adaptive I) No evolution Hardy-Weinberg Equilibrium II) Evolution 1) Genetic Drift a Random (due entirely to chance) changes in allele frequency within a population across generations b Can lead to random loss of allele = loss of genetic diversity
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10.22.07 - H-W Equib. - Darren Rothberg Biol 105 Evolution...

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