Founder Effect Calculator

The founder effect describes how a small group breaking away from a larger population can dramatically shift gene frequencies — sometimes causing rare traits to become common or disappear entirely. Enter the initial frequency of allele A, number of founders, generations to simulate, and population growth rate into the Founder Effect Calculator to see the final allele A frequency and frequency change. Optionally add a bottleneck generation and selection coefficient to model more complex scenarios — outputs also include genetic diversity (2pq), drift variance, and final effective population size.

Frequency of dominant allele in source population

Total number of founding individuals

Per generation growth multiplier (1.0 = constant size)

Generation when bottleneck occurs (0 = no bottleneck)

Population size during bottleneck

Selection against allele A (negative = disadvantage)

Results

Final Allele A Frequency

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Frequency Change

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Final Effective Population Size

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Genetic Diversity (2pq)

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Drift Variance

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Results Table

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Frequently Asked Questions

What is the founder effect in population genetics?

The founder effect occurs when a new population is established by a small number of individuals from a larger population, resulting in reduced genetic diversity and altered allele frequencies due to genetic drift.

How does population size affect genetic drift?

Smaller populations experience stronger genetic drift. The variance in allele frequency change per generation is inversely proportional to the effective population size (variance ≈ pq/2Ne).

What is effective population size and why does it matter?

Effective population size (Ne) is the number of individuals contributing genes to the next generation. It's often smaller than the census population and determines the strength of genetic drift and loss of genetic diversity.

How do bottleneck events affect allele frequencies?

Population bottlenecks dramatically reduce population size temporarily, causing strong genetic drift that can significantly alter allele frequencies and reduce genetic diversity permanently.

What role does selection play in founder populations?

Natural selection can counteract or enhance genetic drift effects. In small founder populations, drift may overpower weak selection, but strong selection can still maintain beneficial alleles.

How is genetic diversity calculated and why does it decrease?

Genetic diversity is measured as 2pq (heterozygote frequency under Hardy-Weinberg). It decreases in small populations due to genetic drift causing allele frequencies to move toward fixation (0 or 1).

Can founder effects lead to increased disease frequencies?

Yes, if founders carry disease alleles at higher frequencies than the source population, or if genetic drift randomly increases disease allele frequencies in the small founding population.