Gene Flow Calculators

0 calculators tagged with “Gene Flow”

Gene flow (migration) is the movement of alleles between populations through the physical movement of individuals or gametes. Gene flow homogenizes allele frequencies between populations — counteracting the divergence caused by genetic drift and local adaptation. Gene flow and genetic drift act in opposition: strong gene flow (high migration rate m) keeps populations genetically similar; strong drift (small population size Ne) causes divergence. The equilibrium between drift and gene flow determines population differentiation measured by FST ≈ 1/(1 + 4Nem), where Ne is effective population size and m is migration rate. FST = 0.1 implies Nem ≈ 2.25 migrants per generation.

All Calculators

No calculators found for this topic.

Wright's Island Model

Equilibrium FST ≈ 1/(1 + 4Nem). Nem = effective number of migrants per generation. Nem = 1: FST ≈ 0.20 (moderate differentiation). Nem = 5: FST ≈ 0.05 (little differentiation). Nem = 10: FST ≈ 0.024. Higher gene flow → lower FST → populations more similar. Solve for Nem: Nem = (1/FST − 1)/4.

Effects of Gene Flow

  • Homogenizes allele frequencies between populations
  • Counteracts local adaptation (maladaptive gene flow)
  • Introduces new alleles → increases within-population genetic diversity
  • Reduces inbreeding depression in small populations (genetic rescue)
  • Spreads advantageous alleles between populations

Measuring Gene Flow

FST: indirect estimate; assumes island model at equilibrium. Direct methods: mark-recapture; telemetry; parentage analysis (assign individual parents using microsatellites or SNPs). Landscape genetics: correlate gene flow with habitat features; circuit theory models connectivity.

Human-Mediated Consequences

Habitat fragmentation reduces gene flow → increases drift → inbreeding. Corridors and translocation programs restore gene flow to isolated populations. Invasive species gene flow: hybridization with native species.

Glossary

Gene Flow (Migration)
Movement of alleles between populations through individual migration or gamete dispersal; homogenizes allele frequencies; FST ≈ 1/(1+4Nem); counteracts drift-driven differentiation.
Wright's Island Model
Population genetics model where FST ≈ 1/(1+4Nem); Nem = effective migrants per generation; Nem = 1 → FST ≈ 0.2; Nem = 5 → FST ≈ 0.05; Nem > 4 prevents substantial differentiation.
Genetic Rescue
Fitness improvement in an inbred population from introduction of migrants; breaks up deleterious homozygosity; examples: Florida panther, Isle Royale wolves; Nem as low as 1–2 migrants/generation may suffice.

Frequently Asked Questions

Gene flow = transfer of alleles between populations through migration of individuals or dispersal of gametes (pollen, seeds, spores). Effects: Homogenization: gene flow equalizes allele frequencies between populations → reduces FST. Diversity: introduces new alleles from outside → can increase within-population genetic diversity. Counteracts local adaptation: maladaptive gene flow introduces alleles that are not beneficial in the local environment → reduces fitness. Genetic rescue: introducing migrants to a small, inbred population → reduces inbreeding depression → increases fitness. Evolutionary constraint: high gene flow prevents populations from independently adapting to local conditions.

Wright's island model: at migration-drift equilibrium, FST ≈ 1/(1 + 4Nem). Nem = effective number of migrants per generation. Rearranging: Nem = (1/FST − 1)/4. Example: FST = 0.10 between two bird populations: Nem = (1/0.10 − 1)/4 = (10−1)/4 = 9/4 = 2.25 effective migrants per generation. Interpretation: just 2–3 migrants per generation is sufficient to prevent significant differentiation (FST stays low). Limitations: FST-based Nem assumes island model (random mating within populations; symmetric migration); violation of these assumptions biases estimates. Direct methods (parentage analysis, assignment tests) are more accurate.

Genetic rescue: introduction of migrants from a genetically diverse source population to a small, isolated, inbred population → increases genetic diversity → improves fitness. Mechanism: small isolated populations accumulate deleterious recessive mutations through genetic drift; inbreeding causes homozygosity → recessive alleles expressed → reduced fitness (inbreeding depression). Gene flow from outside: breaks up homozygosity at deleterious loci → recessive deleterious alleles are masked by wild-type alleles → fitness restored. Examples: Florida panther (Felis concolor coryi): critically inbred by 1990s → 8 Texas pumas introduced 1995 → survival, litter size, and health improved dramatically. Isle Royale wolves: isolated island population → severe inbreeding → single migrant wolf introduced 2018 significantly improved genetic diversity.

Habitat fragmentation divides continuous habitat into isolated patches → reduces dispersal between patches → reduces gene flow → populations become more isolated. Consequences: increased genetic drift in small fragments; allele frequency divergence (rising FST); inbreeding → reduced fitness; local extinctions not recolonized. Conservation measures: wildlife corridors: strips of habitat connecting fragments → allow animal movement → maintain gene flow. Example: Florida Wildlife Corridor; highway underpasses/overpasses for wildlife crossing. Translocation: deliberate movement of individuals between populations → supplements or replaces natural gene flow. Landscape genetics: models how habitat features (roads, land cover, topography) impede or facilitate gene flow → guides corridor design.