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Unformatted text preview: 2/1/10 1 194 194 Genetic drift •Genotypic variation is “neutral” •Fate determined by sampling error - ¡nite populations •Theory applied primarily to molecular data A simple example of genetic drift in a population of one sel¡ng individual Gen 1 Aa Gametes AaaaAAaaAAaAAAA AaaAAaaAAAaAaAa aaAAaaaaAaaaA Gen 2 Prob AA = 0.25 Prob Aa = 0.5 Prob aa = 0.25 50% prob that individual (population) is homozygous 195 195 Genetic drift Consider a fair coin that we ¢ip 100 times Expect 50 heads and 50 tails However, there is a distribution of outcomes - binomial sampling dist. Prob of i heads in n trials = n p i (1-p) n-i i This is analagous to a population of size 2N gene copies (50 diploids) and two alleles with frequency p and q (freq 0.5). 2N gametes are sampled each gen. to create a new group of N zygotes Expected freq in the next gen is p (and q), but variance is pq/(2N) “n choose i” 2/1/10 2 196 196 Genetic drift Alternatively, consider a new mutation (the “a” allele) in a population...
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- Winter '10
- Population Genetics, effective population size, Population bottleneck, Ridley