Estimate how much allele frequency can shift by drift in a finite effective population.
Answer
0.0354
One-generation standard deviation
Approx. 95% range after generations: 0.1973 - 0.8027
Heterozygosity remaining: 90.5%
Eventual fixation probability: 50%
Eventual loss probability: 50%
This is a neutral drift approximation. The expected allele frequency stays p, while variance increases over generations.
Var(p') = p(1 - p) / (2Ne)For multiple generations, heterozygosity is retained by approximately (1 - 1/(2Ne))^t under neutral drift.
| Symbol | Variable | Description |
|---|---|---|
| p | Allele frequency | Starting frequency of the allele. |
| Ne | Effective population size | Population size that determines drift strength. |
| t | Generations | Number of generations over which drift accumulates. |
Enter p
Use the starting allele frequency from 0 to 1.
Enter Ne
Use effective population size, not necessarily census population size.
Read drift spread
The answer area shows one-generation drift and a multi-generation frequency range.
Smaller Ne creates larger random frequency changes and faster loss of heterozygosity.
| Output | Meaning |
|---|---|
| Standard deviation | Expected one-generation random spread |
| 95% range | Approximate multi-generation spread around p |
| Fixation probability | Neutral probability the allele eventually reaches frequency 1 |
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