# Genetic drift

Random changes in allele frequencies from one generation to the next, caused by chance. The effect is strongest in small populations. Bottlenecks and founder effects are examples.

Biology (university) · Part 08: Evolution and diversity of life · Card 3 of 8 · Last updated 2026-10-19

## Analogy

Flipping a coin 10 times versus 1,000 times: small samples wander far from 50:50.

## In practice

After a disease cuts a population to a handful, the survivors' alleles may not match the original mix.

## Practice

### Flashcards

- **Which populations are most affected by genetic drift?** Small populations.
- **What is a bottleneck?** A sharp fall in population size that leaves a small, random sample of 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

### What is the founder effect?

The founder effect occurs when a small group leaves a large population to start a new one. The new population has only a sample of the original alleles, and rare alleles may become much more common by chance. Some genetic diseases are unusually frequent in communities that began with a few founders.

### Does drift help or harm a population?

Drift is random, so it is neither. But in small populations it can wipe out useful alleles and fix harmful ones, reducing genetic variation. A population with little variation has less ability to adapt to change, which is a concern for endangered species with small numbers.

## Related concepts

- [Gene flow](https://studyvisually.com/learn/science/biology-university/biology-university-part-8/biology-university-part-8-concept-4)
- [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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