← Genetic variation and change
Population genetics: drift, bottlenecks & founder effect
Small populations lose genetic variation faster than large ones — three named mechanisms, easily confused with each other.| Mechanism | What causes it | Effect on variation |
|---|---|---|
| Genetic drift | Random chance, generation to generation — stronger the smaller the population | Allele frequencies wander randomly; rare alleles can be lost purely by chance |
| Population bottleneck | A sudden, sharp population crash (disaster, over-hunting, disease) | Only the alleles the SURVIVORS happen to carry remain — variation drops sharply |
| Founder effect | A new population starts from a SMALL number of individuals | The new population's gene pool reflects only the founders' alleles, not the source population's full variation |
| Gene flow | Migration of individuals between populations | Can INCREASE variation in the receiving population, or homogenise two populations toward each other |
A bottleneck and a founder effect both shrink genetic variation, but a bottleneck happens to an EXISTING population that crashes, while a founder effect happens when a NEW population is started by a small group that leaves the main population.
✕A small population magnifies genetic drift — say why
In a large population, chance fluctuations in which individuals reproduce average out and allele frequencies stay fairly stable. In a SMALL population, the same random events can eliminate or fix an allele in just a few generations, because each individual is a much larger share of the total gene pool. Always name the population SIZE as the reason drift matters more.Practice for this standard covers the whole topic — flashcards and quiz.