# Gene flow

The movement of alleles between populations when individuals or gametes move. It makes populations more similar and adds new variation.

Biology (university) · Part 08: Evolution and diversity of life · Card 4 of 8 · Last updated 2026-10-19

## Analogy

Seeds blown across a fence into a neighbour's garden.

## In practice

Pollen carried by wind between two meadows brings alleles from one to the other.

## Practice

### Flashcards

- **How does gene flow affect populations?** It makes them more genetically similar and can add new alleles.

### Interview questions

**List the conditions for Hardy-Weinberg equilibrium and explain why real populations rarely meet them.**

- No mutation
- No selection
- No gene flow
- Large population, no drift
- Random mating

## Questions people ask

### How does gene flow affect speciation?

Gene flow keeps populations genetically similar, so it works against the splitting of one species into two. When a barrier stops gene flow, the populations can diverge through selection and drift. This is why isolation is a key step in forming new species.

### Can gene flow happen between species?

Occasionally. When closely related species hybridise and the hybrids can reproduce, alleles move between them. This is called introgression. Modern humans, for example, carry a small percentage of Neanderthal DNA from interbreeding. It is much more common in plants than animals.

## Related concepts

- [Genetic drift](https://studyvisually.com/learn/science/biology-university/biology-university-part-8/biology-university-part-8-concept-3)
- [Hardy-Weinberg equilibrium](https://studyvisually.com/learn/science/biology-university/biology-university-part-8/biology-university-part-8-concept-5)
- [Natural selection](https://studyvisually.com/learn/science/biology-university/biology-university-part-8/biology-university-part-8-concept-1)
- [Fitness](https://studyvisually.com/learn/science/biology-university/biology-university-part-8/biology-university-part-8-concept-2)

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