6_EvolMech2

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

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1 Evolutionary Mechanisms 2 23.3-23.4
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2 Evolutionary Processes Mutation and sexual recombination produce new variation Selection, drift and gene flow alter a population’s genetic composition
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3 Evolutionary Processes Mutation and sexual recombination produce new variation Selection, drift and gene flow alter a population’s genetic composition
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4 Natural Selection Differential survival and/or reproduction results in certain alleles being passed to the next generation in greater proportions
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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
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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!
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7 Strength of selection is proportional to population size QuickTime Q and a TIFF (Uncompressed) decompressor are needed to see this picture.
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8 Evolutionary Processes Mutation and sexual recombination produce new variation Selection, drift and gene flow alter a population’s genetic composition
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9 Random Genetic Drift Changes in allele frequencies within populations which result from chance variation in individual survival and reproduction Most important in small populations Can result in maladaptive evolution
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This note was uploaded on 02/19/2008 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 - Evolutionary Mechanisms 2 23.3-23.4 1...

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