What is genetic drift?

Genetic drift is the random change in allele frequency from generation to generation caused by chance sampling. In a small population, a few individuals may by luck fail to reproduce, so their alleles are lost even if they were not harmful. Drift is stronger in smaller populations.

What is the Wright-Fisher model?

The Wright-Fisher model assumes each new generation of 2N gene copies is formed by sampling independently and with replacement from the previous generation. Each copy independently has probability p (current allele frequency) of being the focal allele. This gives a binomial sampling process.

What does fixation mean?

Fixation occurs when an allele reaches a frequency of 1.0 (100%), meaning every individual in the population carries it. Once fixed, the allele cannot be lost without new mutation. The probability of fixation for a neutral allele starting at frequency p is exactly p.

Why do different runs end differently?

Each run uses independent random sampling, so outcomes differ by chance. This captures the stochastic nature of drift. Running many replicates (e.g., 20) shows the full range of possible trajectories from the same starting conditions.

How does population size affect drift?

Larger populations experience weaker drift because random sampling error averages out across more individuals. Smaller populations drift faster, reaching fixation or loss in fewer generations. Try N=10 versus N=500 to see the difference.

Is mutation or selection modeled here?

No. This simulator models pure neutral drift with no selection, mutation, migration, or non-random mating. It isolates the effect of finite population size on allele frequency change.

Genetic Drift Simulator

Name: Genetic Drift Simulator
Availability: InStock
Author: Nham Vu

Simulate how random sampling causes allele frequencies to drift over generations in a finite population, showing fixation and loss events.

Simulation Parameters

Population size (N)

Number of diploid individuals (2–2000)

Initial allele frequency (p)

Starting frequency of allele A (0.01 – 0.99)

Number of generations

Simulation length (10 – 500)

Number of runs

Independent simulation lineages (1 – 30)

Quick Presets

Allele Frequency Over Generations

Each line is an independent simulation run. Dashed lines mark fixation (p=1) and loss (p=0).

Set parameters and click Run Simulation.

Summary