0.00125
0.035355
0.5
0.475555
95.11
%
4.89
%
0.04889
99.5
%
0.00125
0.035355
0.5
0.475555
95.11
%
4.89
%
0.04889
99.5
%
The Genetic Drift Calculator quantifies the expected magnitude of random allele frequency change in a finite population. Genetic drift is the stochastic change in allele frequencies due to random sampling of gametes during reproduction. Its effects are strongest in small populations and can lead to allele fixation or loss independent of natural selection.
Enter the initial allele frequency, effective population size, and number of generations to estimate drift variance and heterozygosity loss over time.
The variance in allele frequency due to drift in one generation is:
Var(Δp) = p × q / (2 × Ne)
Where p and q are the allele frequencies and Ne is the effective population size. Heterozygosity decays geometrically over generations:
H(t) = H(0) × (1 − 1/(2Ne))^t
Where H(0) = 2pq is the initial heterozygosity and t is the number of generations. The fraction of heterozygosity lost after t generations is 1 − (1 − 1/(2Ne))^t.
Inputs
Results
With Ne of only 20, after 50 generations about 71.4% of heterozygosity is lost. The initial H=0.5 has declined to 0.286, showing severe genetic erosion.
Inputs
Results
With Ne of 10,000, drift is negligible: only 0.5% of heterozygosity is lost after 100 generations, and allele frequencies remain very stable.
Natural selection is directional, favoring alleles that increase fitness, and is more effective in large populations. Genetic drift is random, affecting all alleles regardless of fitness, and is strongest in small populations. In very small populations, drift can overpower selection, causing harmful alleles to become fixed or beneficial alleles to be lost by chance.
Each generation, approximately 1/(2Ne) of the remaining heterozygosity is lost to drift. This means smaller populations lose diversity faster. After 2Ne generations, about 63% of original heterozygosity is lost. This simple rule helps conservation biologists quickly assess the vulnerability of small populations.
Once alleles are lost from a population, they can only return through mutation (very slow) or gene flow from other populations. This is why maintaining large effective population sizes and connectivity between populations is crucial for conservation. Bottleneck events can permanently reduce diversity.
Roboculator Team
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