5_EvolMech1

5_EvolMech1 - Evolutionary Mechanisms I 22.1-22.2...

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1 Evolutionary Mechanisms I 22.1-22.2 2 Populations evolve, individuals do not Simpson video 3 The Modern Synthesis • Established in the 1930s and 1940s • Connected the units of evolution (genes) with the mechanism of evolution (selection on populations) • Integrated Darwinian evolution with Mendelian genetics + 4 Architects of the modern synthesis JBS Haldane G Ledyard Stebbins Theodosius Dobzhansky Sewall Wright 5 Hardy Weinberg principle • Given a series of assumptions, allele frequencies and genotype frequencies will not change between generations • The assumptions are: No selection No mutation No migration Infinitely large population Random mating AA Aa aa AA Aa aa aa Generation 1, “Gene pool” Generation 2, allele freq p and q allele freq p and q AA Aa aa AA Aa aa aa A a a A A a a A a If these assumptions are met, allele and genotype frequencies will not change between generations
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2 7 Some terminology • Imagine a populations made up of 100 diploid individuals: 40AA, 40Aa and 20aa • The genotype frequencies are?………. • The allele frequencies are?……. • The genotype numbers are?……. • The allele numbers are…. . 8 Remember the multiplication and addition rules? If you just roll one die, what’s the chance of getting a 4? What’s the chance of getting 4 twice in a row? The combined probability of independent events occurring together is the product of their individual probabilities 9 If you just roll one die, what’s the probability of getting either a 4 or a 6? The combined probability of 2 mutually exclusive events is the sum of their individual probabilities 10 A A a a 0.5 0.5 Eggs Sperm Under Hardy-Weinberg equilibrium, allele frequencies predict genotype frequencies Here’s a numerical example using Punnett squares: 0.5 0.5 0.25 AA 0.50 Aa 0.25 aa Freq A = p = 0.5 Freq a = q = 0.5 .25 AA .25 aA .25 Aa .25 aa 11 A A a a p q Eggs Sperm Here’s the same thing using symbols. .. p q p 2 AA 2pq Aa q 2 aa Always check your work: p + q = 1 p 2 + 2pq + q 2 = 1 p 2 AA pq aA pq Aa q 2 aa 12 The same principle applies when there are more than 2 alleles (although we’ll need to use more than p and q) Alleles: A 1 A 2 A 3 A 4 A 5 A 6 ...
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5_EvolMech1 - Evolutionary Mechanisms I 22.1-22.2...

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