GEEslidesSet5 23March2010

GEEslidesSet5 23March2010 - Ch 11 Sexual Selection...

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Ch 11 Sexual Selection
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MUTATION SELECTION DRIFT MIGRATION POPULATIONS Phenotypic Evolution: Process + + +/- -
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HOW DOES MUTATION CHANGE ALLELE FREQUENCIES? Assume: a single autosomal locus with 2 alleles. Frequency (A) = p Frequency (a) = q Suppose that A mutates to a at rate u : A a = u And a mutates to A at a rate v : a A = v
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Change in p by mutation from generation t t + 1: p t+1 = p t (1-u) + q t (v) Since p + q = 1, q = 1 - p we can substitute (1-p) for q: p t+1 = p t (1-u) + (1-p t ) (v) A alleles remaining as A a alleles mutating to A Original allele Next generation How fast mutation can substitude
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Example: If p and q = 0.5, And u = 0.0001 and v = 0.00001 p t+1 = p t (1-u) + (1-p t ) (v) p t+1 = 0.5 (1 - 0.0001) + (1 - 0.5) (0.00001) = 0.499955 After one generation to the next
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At Equilibrium: p x u = q x v , And p = v / ( u + v ) , q = u / ( u + v ) If u = 0.0001 and v = 0.00001, p = 0.091 and q = 0.909 However, if p starts out at 1.0, it would take about 40,000 generations to reach p = 0.091!!! Forth mutaion has to = back mutation rate The direction from A to a is higher than reverse b/c p=0.091 that mean only 0.091 is still A.
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GENETIC DRIFT Alteration of gene frequencies due to chance ( stochastic U & & =random ) effects. Most important in small populations. Tends to reduce genetic variation as the result of extinction of alleles. Generally does not produce a fit between organism and environment; can, in fact, result in nonadaptive or maladaptive changes.=>not advantageous Random changes in the frequencies of existing alleles over time in a population
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COALESCENCE THEORY-gene specific Time coalescence U &   =maternal mitochondria DNA =>mito evolution-doesn’t go through recombinations If all have boys, then stop passing mitochondria DNA Trace back from now to anscestor
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COALESCENCE THEORY We can trace the descendents of a gene just like a haploid organism. If we look back in time, all of the current gene copies shared a single common ancestor. THE GENEALOGY OF THE PRESENT SEQUENCES COALESCES TO A SINGLE COMMON ANCESTOR.
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GEEslidesSet5 23March2010 - Ch 11 Sexual Selection...

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