Genetic drift — Science definition
Random, chance changes in allele frequencies from one generation to the next; its effect is strongest in small populations, as in the bottleneck and founder effects.
Where it is taught
- Speciation & Mechanisms of Evolution — Evolution, Ancestry & Biodiversity, Life Science: Biology, Grade 10
In use
Genetic drift changes frequencies through chance sampling, especially in small populations.
Speciation & Mechanisms of Evolution
Questions using genetic drift
Problem 1
- small populations
- very large populations
- populations with high gene flow
- populations under strong natural selection
Answer and explanation
small populations
Drift is random change in allele frequencies. In small populations, chance events (like which few individuals happen to reproduce) can swing allele frequencies dramatically; in large populations these chance effects average out.
Problem 2
- very large populations
- small populations
- populations with high gene flow
- populations with no mutation
Answer and explanation
small populations
Chance variation in which individuals reproduce has proportionally larger effects when the population is small, so frequencies can shift substantially without selection.
Problem 3
Answer and explanation
Natural selection changes frequencies because particular heritable variants raise their bearers' reproductive success, so the change is related to the alleles' effects. Genetic drift changes frequencies through chance in which individuals happen to reproduce, so the change is unrelated to the alleles' effects and can even reduce the frequency of a beneficial allele. Both alter populations, but only selection produces a consistent relationship between an allele's effect and its fate.
Response criteria
- State a biologically accurate conclusion.
- Show the data, mechanism, or calculation that supports it.
- Include units, conditions, or limits where relevant.