Genetic drift simulation: the frequency of allele A over eighty generations for a founding population you set, compared with a large population of five hundred, with founder and bottleneck scenarios

Chance alone can delete an allele

Genetic drift is sampling error. Each generation, the alleles of the newborns are a random draw from the parents' gene pool, and a small draw misses things. Lower the founding size and watch one colour take over the chart; raise it and watch the frequency barely move while the generations tick by.

Drift simulator
Gen 0 of 80
Change the founding size and watch the two colours.
N 20 · gen 0 · p 0.50 · 2pq 0.50
Scenario
Founding size N20
10 50 100 200
Allele A frequency p
0.50
Heterozygosity 2pq
0.50

Know This

Genetic drift is sampling error: small populations lose alleles by chance, and large-scale studies need huge samples so real patterns rise above the same noise.