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Population Genetics Hardy Weinberg Equilibrium

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Population Genetics Hardy-Weinberg Principle/equilibrium –G. H. Hardy (1877- 1947) English mathematician –Wilhelm Weinberg (1862-1937) German physician & geneticist

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Population Genetics Essential concept: Gene pool –“Collection” of all alleles of all individuals in a population –Within a gene pool, alleles have frequencies –Allele frequency = proportion of an allele among all alleles of a given gene.

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Allele Frequency There are 2015 individuals in a population. –How many alleles exist for a specific trait that follows mendelian inheritance? 4030

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Allele Frequency There are 2015 individuals (4030 alleles) in a population. –If 172 of those alleles are recessive, what is the frequency of the recessive allele? –What is the frequency of the dominant allele? 172/4030 = 0.04, so 4% 3858/4030 = 0.96, so 96%

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Allele Frequency There are 312 individuals in a population. –If 172 of those alleles are recessive, what is the frequency of the recessive allele? 28%(172/624) –What is the frequency of the dominant allele? 72% (624-172)/624

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Allele Frequency By convention, we use p to represent the dominant allele. By convention, we use q to represent the recessive allele. p + q = 1

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Allele Frequency There are 312 individuals in a population. –If 172 of those alleles are recessive, what is the frequency of the recessive allele? 28%(172/624) –What is the frequency of the dominant allele? 72% (624-172)/624

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Population Genetics If we know allele frequencies, we can calculate genotypic and phenotypic frequencies.

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Population Genetics Let’s say a population contains 70% dominant and 30% recessive alleles…

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Hardy Weinberg Equilibrium p 2 + 2pq + q 2 = 1

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Population Genetics Hardy-Weinberg Principle/equilibrium –Allele frequencies remain unchanged generation to generation

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Population Genetics Hardy-Weinberg Principle/equilibrium –Mathematical model –Assumptions/conditions Large population Random interbreeding No mutation No gene flow (migration among populations) No selection

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Hardy Weinberg Conditions MUST be a large population –Founder effect –Bottleneck effect

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Bottleneck

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Hardy Weinberg Conditions MUST be a large population –Founder effect –Bottleneck effect –Genetic drift

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Genetic Drift

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Hardy Weinberg Conditions Must have Random breeding Violations of conditions: Sexual selection & female choice –Pea-fowl Male dominance, combat –Big-horn sheep

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Hardy Weinberg Conditions No immigration / emigration

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Hardy Weinberg Conditions No migration between populations

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Hardy Weinberg Conditions No selective pressure Heterozygote advantage

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There are two color morphs of tigers. The gene that results in the white color morph is recessive. Let’s say white tigers make up 10% of a population. How do we calculate genotype frequencies?

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Calculations: If 10% of the population is white, q 2 =.10 If q 2 =.10, q =.32 If q =.32, p =.68 If p =.68, p 2 =.46 2pq =.44 Genotype Frequencies p 2 =.46 2pq =.44 q 2 =.10

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