Genetic Bottleneck & Founder Effect

Population Setup

Carrying capacity K 200

Founder size N_b 8

Recovery growth rate r 0.25

Alleles at locus 6

Live Readouts

Generation

Population N

200

Alleles remaining

6 / 6

Heterozygosity H_e

0.833

How it works

Each of the N individuals carries one allele at a single locus (haploid model). Every generation is a Wright-Fisher resampling: the next generation of size N′ is drawn by picking alleles independently at random, with replacement, from the current generation's allele pool — exactly as a finite population reproduces from a finite gene pool.

P(pick allele i) = n_i / N        (multinomial sampling)
N(t+1) = N(t) + r·N(t)·(1 − N(t)/K)   (logistic regrowth toward K)
H_e = 1 − Σ p_i²                  (expected heterozygosity)

A bottleneck collapses N to a handful of founders N_b, sampled from the current pool. Alleles that only a few founders happened to carry are likely to vanish entirely by chance — this is the founder effect. Because H_e depends on allele counts, not population size, diversity lost in the crash is not restored by regrowth alone: only new mutation (not modelled here) can bring it back. Small N also means faster ongoing genetic drift each generation, visible as the readouts keep drifting even without another bottleneck.

Carrying capacity K — the population size the habitat can support once fully regrown.
Founder size N_b — how many individuals survive the crash; smaller means faster diversity loss.
Recovery growth rate r — how quickly the population regrows toward K after a crash.
Alleles at locus — how many distinct alleles the starting population carries, shown as sphere colours.

Real-world relevance: cheetahs, northern elephant seals and Amish founder populations all show this exact signature — a historical population crash followed by low genetic diversity that persists for many generations afterward.

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