Genetic Drift Analyzer

Simulate and analyze genetic drift in populations. Understand how random chance affects allele frequencies over generations.

Wright-Fisher Model
Moran Model
10 100 1000
10% 80% 100%
1% 50% 99%
10 100 500
Simulation Speed:
Slow Medium Fast
Simulation Progress 0%
Generation: 0
Allele A:
50.0%
Allele B:
50.0%
100
Population Size
80
Effective Size
0
Current Generation
50.0%
Fixation Probability
50.0%
Heterozygosity
0.25
Variance
-
Time to Fixation
0.005
Drift Strength

Multiple Simulation Results

Understanding Genetic Drift

Genetic drift is the change in the frequency of an existing gene variant (allele) in a population due to random sampling of organisms. The alleles in the offspring generation are a random sample of those in the parent generation, and chance plays a role in determining whether a given individual survives and reproduces.

Key Insight: Genetic drift has a larger effect in small populations and can lead to the loss of genetic variation, fixation of alleles, and divergence between populations.

Population Genetics Models

1

Wright-Fisher Model: The classic model of genetic drift with discrete generations. Each generation is formed by random sampling of alleles from the previous generation. This model assumes constant population size and random mating.

2

Moran Model: A model with overlapping generations where individuals reproduce and die one at a time. This model more closely resembles populations with continuous reproduction rather than discrete generations.

Effective Population Size

The effective population size (Nₑ) is the size of an idealized population that would experience the same amount of genetic drift as the actual population. Real populations often have Nₑ smaller than the census population size due to:

  • Unequal sex ratios
  • Fluctuating population sizes
  • Variation in reproductive success
  • Overlapping generations

Conservation Importance: Effective population size is crucial for conservation genetics. Small Nₑ increases the rate of genetic drift, leading to loss of genetic diversity and increased inbreeding, which can reduce population viability.

Mathematical Properties

Property Formula Explanation
Fixation Probability Pfix = p For a neutral allele, probability of fixation equals its current frequency
Rate of Heterozygosity Loss Ht = H0(1 - 1/(2Ne))t Heterozygosity decreases over time due to genetic drift
Variance in Allele Frequency σ2 = p(1-p)/(2Ne) Variance in allele frequency change per generation
Time to Fixation T ≈ 4Ne generations Average time for a neutral allele to become fixed

Frequently Asked Questions

The Wright-Fisher model assumes discrete generations where the entire population is replaced at once. The Moran model assumes overlapping generations where individuals reproduce and die one at a time. The Moran model has a slower rate of genetic drift (by a factor of 2) compared to the Wright-Fisher model with the same population size.

Effective population size determines the rate of genetic drift and inbreeding. A small Nₑ means faster loss of genetic diversity, increased inbreeding, and higher probability of fixation of deleterious alleles. Conservation efforts often focus on maintaining large effective population sizes to preserve genetic diversity.

Yes, in small populations, genetic drift can overcome natural selection, allowing deleterious alleles to become fixed or beneficial alleles to be lost. The relative strength of selection vs. drift depends on the selection coefficient (s) and effective population size (Nₑ). When |s| < 1/(2Nₑ), genetic drift dominates over selection.