Wright-Fisher Drift Variance

Problem

One step of Wright-Fisher drift changes an allele frequency p by an amount with mean 0 and variance:

Var(delta p) = p * (1 - p) / (2N).

Return 0.0 for N <= 0.

Hint

The next count is Binomial(2N, p), so the frequency variance is p(1 - p) / (2N).

case 1

in: [0.5,100]

expected: 0.00125

case 2

in: [0.5,10]

expected: 0.0125

case 3

in: [0.2,50]

expected: 0.0016000000000000003

case 4

in: [0.5,0]

expected: 0

Starter codePython

def wright_fisher_drift_variance(p, N):
    # Your code here
    pass

4 test cases · run your code against them in the editor