6_EvolMech2

6_EvolMech2 - 1 1 Evolutionary Mechanisms 2 23.3-23.4 2...

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Unformatted text preview: 1 1 Evolutionary Mechanisms 2 23.3-23.4 2 Evolutionary Processes Mutation and sexual recombination produce new variation Selection, drift and gene flow alter a populations genetic composition 3 Evolutionary Processes Mutation and sexual recombination produce new variation Selection, drift and gene flow alter a populations genetic composition 4 Natural Selection Differential survival and/or reproduction results in certain alleles being passed to the next generation in greater proportions 5 How does selection affect HWE? Population size: 1000 individuals Alleles: A 1 A 2 Frequencies: 0.5 0.5 Genotypes: A 1 A 1 A 1 A 2 A 2 A 2 Frequencies: 0.25 0.50 0.25 Count: 250 500 250 Fitness (w) 0.6 0.8 1.0 6 What are the allele frequencies after selection? First, calculate the new genotype counts (= old genotype counts * w): A 1 A 1 A 1 A 2 A 2 A 2 Total 250(0.6) 500(0.8) 250(1.0) 150 400 250 800 Now calculate the new allele frequencies: A 1 : (2*150 + 400)/ 1600 = 700/1600 = 0.438 A 2 : (400 + 2*250)/ 1600 = 900/1600 = 0.562 The frequency of A 2 has increased! 2 7 Strength of selection is proportional to population size 8 Evolutionary Processes Mutation and sexual recombination produce new variation Selection, drift and gene flow alter a populations genetic composition 9 Random Genetic Drift Changes in allele frequencies within populations which result from chance...
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This note was uploaded on 03/27/2008 for the course BISC 120Lg taught by Professor 11:00-01:50pm during the Fall '06 term at USC.

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6_EvolMech2 - 1 1 Evolutionary Mechanisms 2 23.3-23.4 2...

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