g640chp24 - finite population allele frequencies subject to...

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FINITE POPULATION SIZE II finite population allele frequencies subject to random change average change predictable over many replicate populations AVERAGE CHANGE = 0 finite population allele frequencies subject to random change variance of change predictable from population size variance increases as population size decreases VARIANCE OF ALLELE FREQUENCY CHANGE = pq / 2N finite population allele frequencies subject to random change future change independent of past behavior finite population allele frequencies subject to random change genetic variation decreases each generation decrease in heterozygosity increasing probability of fixation or loss PROPORTION OF REPLICATE POPULATIONS WHICH SEGREGATE FOR MORE THAN ONE ALLELE DECREASES how fast is variation lost? consider a population of size 2N genes at generation zero - mark all copies as different
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how fast is variation lost? choose a pair of genes what is the probability that the two genes are identical? how fast is variation lost? 1/2N x 1/2N = (1/2N) 2 how fast is variation lost? TOTAL PROBABILITY OF HOMOZYGOSITY = 1/2N 1/2N x 1/2N = (1/2N) 2 BUT THERE ARE 2N POSSIBLE ALLELES THAT COULD HAVE BEEN CHOSEN AS THE FIRST COPY how fast is variation lost? At the first generation: H 1 = (1 - 1/2N) H 0 how fast is variation lost? At the first generation: H 1 = (1 - 1/2N) H 0 At second generation: H 2 = (1 - 1/2N) H 1 = (1 - 1/2N) 2 H 0 how fast is variation lost? At the first generation: H 1 = (1 - 1/2N) H 0 At second generation: H 2 = (1 - 1/2N) H 1 = (1 - 1/2N) 2 H 0 At any future generation: H t = (1 - 1/2N) t H 0
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how fast is variation lost? heterozygosity declines at a rate 1/2N e per generation Loss of variation in populations of different size Lacy, 1987 Loss of variation in populations of different size loss of variability by genetic drift how fast is variation lost? calculating loss of alleles is not as easy evaluated using computer simulation loss of rare alleles as a function of population size Ne #of alleles remaining after one generation ----------------------------------------------------------- 1000 ~8.00 100 7.81 10 3.86 5 2.69 1 1.35 population has 8 alleles to start: at frequencies: .80,.07,.03,.03,.02,.02,.02,.01
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effective population size rate of change of gene frequency, p, depends on several factors which effectively change (usually decrease)
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g640chp24 - finite population allele frequencies subject to...

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