MIGRATION - the A allele in population x in the next...

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MIGRATION In population genetics, the term "migration" is really meant to describe Gene flow , defined as the movement of alleles from one area (deme, population, region) to another. Gene flow assumes some form of dispersal or migration (wind pollination, seed dispersal, birds flying, etc.) but dispersal is not gene flow (genes must be transferred, not just their carriers) We can describe gene flow (migration) in a manner similar to mutation. Consider two populations, x and y with frequencies of the A allele of p x and p y . Now consider that some individuals from population y migrate into population x. The proportion of these y individuals that become parents in population x in the next generation = m . After the migration event, population x can be considered to consist of migrant individuals (proportion m) and non-migrant individuals (proportion [1-m]). Thus the frequency of
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Unformatted text preview: the A allele in population x in the next generation (p x t+1 ) is just the frequency in the non-migrant portion (= p x [1-m]) plus the frequency in the migrant portion (p y m). Thus: p x t+1 = p x t [1-m] + p y m . The change in allele frequency due to gene flow is p = (p x t+1 ) - p x t which is just; [p x t [1-m] + p y m] - p x t Multiplying through and canceling terms leaves us with: p = -m(p x t- p y t ) . This makes intuitive sense: the change in p depends on the migration rate and the difference in p between the two populations. If we considered a grid or array of populations and focus on one of those populations as the recipient population with all other populations contributing equally to it, then p y would be replaced by the average p for all the other populations. Many scenarios are possible....
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