Chapter 25__upload_Genetics of Populations

Applies to all diploid sexual organisms how can we

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Unformatted text preview: cal population Theoretical genetic models: genetic Hardy-Weinberg Equilibrium Hardy-Weinberg Hardy-Weinberg Equilibrium Principle Principle Designed as a simple model to account for and estimate how alleles behave in populations Develops a null model for behavior of genes in populations Model specifies what will happen to frequencies of alleles and genotypes Applies to all diploid sexual organisms Hardy-Weinberg model Hardy-Weinberg Assumptions of Hardy-Weinberg There is no selection All members contribute equally to gene pool There is no mutation No new alleles are created There is no migration All alleles stay in gene pool There is a large population size No random events = genetic drift Panmixia Mates are chosen randomly Hardy-Weinberg Equilibrium Principle Principle Population = group of interbreeding individuals and their offspring Life Cycle Adults produce gametes Gametes combine to make zygotes Zygotes grow up to become next generation of adults Track fate of Mendelian genes across generations in a population Find out if particular alleles become more or less common over time Hardy-Weinberg Hardy-Weinberg Example: Imagine that mice have a particular locus A with two alleles: A and a (Could also call them A1 and A2) Track these alleles and follow them through one complete turn of the life cycle to see if frequencies change Hardy-Weinberg Hardy-Weinberg Example: Assume adults choose their mates at random Matings are random within the gene pool Diploid organisms (2N), so each has two alleles for the A locus Meiosis (during gametogenesis) caused one allele (either A or a) to be in each gamete for the A locus Hardy-Weinberg Hardy-Weinberg Example: Imagine 60% of eggs and sperm contain allele A and 40% contain allele a Frequency of A allele in gene pool is 0.6, of a allele is 0.4 When egg and sperm meet, what proportion of genotypes will be AA? 60% egg will be A, 60% sperm will be A: 0.6 X 0.6 = 0.36 36% of zygotes will have genotype AA 60% A, 40% a Hardy-Weinberg Hardy-Weinberg Example: How many would be aa? 0.4 X 0.4 = 0.16 How many would be Aa? 0.6 X 0.4 X 2 = 0.48 Notice that 0.36 + 0.48 + 0.16 = 1 All possible genotype frequencies will add up to one Hardy-Weinberg Equilibrium Principle Principle If zygotes grow up, what will the frequency of A in the next generation be? AA is 36% All gametes carry A Aa is 48% Half will carry A, half will carry a aa is 16% All gametes carry a Frequency of A in next generation will be: 0.36 + (1/2)0.48 = 0.6 Frequency of a will be: 0.16 + (1/2)0.48 = 0.4 Hardy-Weinberg Hardy-Weinberg Example: 0.6 + 0.4 = 1 Allele frequencies are the same as in the first generation Allele frequencies are in equilibrium The population does not evolve If a population is in Hardy-Weinberg Equilibrium it will never evolve (=allele frequencies in pop. will NEVER change) This is true regardless of starting allele frequencies Hardy-Weinberg Equilibrium Principle Principle The General Case Imaginary population Single locus with A and a...
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This document was uploaded on 09/17/2013.

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