Genetic Drift – Wright-Fisher Model

Population N200 Initial freq p₀0.50 Generations200 Replicates10

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Fixed A₁

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Fixed A₂

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Lost

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Segregating

In the Wright-Fisher model, a diploid population of size N is sampled each generation by binomial sampling:

p' ~ Binomial(2N, p) / 2N

Drift variance per generation:

Var(Δp) = p(1−p) / 2N

Expected fixation time for neutral alleles: ~4N generations. Probability of fixation starting at frequency p is simply p (Kimura 1962).

Smaller N → stronger drift → faster fixation/loss.