AP Biology: Genetic Drift and Bottlenecks Practice Questions
Practice genetic drift and bottleneck effects with original AP Biology multiple-choice questions. Each item focuses on chance events, small population size, and how random sampling can change allele frequencies.
Free original practice questions for study purposes. Open Exam Prep is an independent study resource and is not affiliated with, endorsed by, or sponsored by the makers of AP Exams.
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Answer the questions below — you get instant feedback and a full explanation for each.
1. A storm randomly kills most individuals in a small island beetle population. The survivors happen to carry allele B at a much lower frequency than before the storm. Which mechanism best explains the change?
Explanation. A bottleneck is a sharp, chance reduction in population size. Because the survivors are a random sample, allele frequencies can shift even if the alleles do not affect survival.
2. Why does genetic drift usually have a stronger effect in small populations than in large populations?
Explanation. In small populations, chance differences in which individuals reproduce can noticeably change allele frequencies from one generation to the next.
3. A few birds colonize an empty island. By chance, the colonists carry only a subset of the alleles found in the mainland population. This is an example of which process?
Explanation. The founder effect is genetic drift that occurs when a new population starts from a small, nonrepresentative sample of a larger population.
4. After a bottleneck, which outcome is most likely even if the population later grows back to its original size?
Explanation. If alleles are lost during the bottleneck, population growth alone does not recreate them. New mutation or gene flow would be needed to restore lost variation.
5. A neutral allele rises from 0.12 to 0.70 in a small isolated population over several generations. The allele does not affect survival or reproduction. Which explanation is most consistent?
Explanation. Genetic drift can make neutral alleles increase or decrease in frequency by chance, especially in small isolated populations.
6. Which comparison best distinguishes a bottleneck effect from a founder effect?
Explanation. Both are forms of genetic drift, but bottlenecks involve survival after a major reduction, while founder effects involve colonization by a small group.
7. A class simulates allele frequencies by drawing colored beads from a bag. Which setup would show the strongest drift from one generation to the next?
Explanation. A smaller draw has greater sampling error, so allele frequencies are more likely to shift by chance.
8. Which observation would most directly support the idea that a population experienced a recent bottleneck?
Explanation. A severe bottleneck can remove alleles across the genome, leaving unusually low genetic variation relative to populations that did not shrink.
9. Which statement about genetic drift is accurate?
Explanation. Genetic drift is a chance process. It is not directed by fitness and can move allele frequencies up or down.
10. A rare allele is present in 2 of 20 individuals before a flood. None of the 5 survivors carry it. What happened to the allele in the surviving population?
Explanation. If no survivors carry the rare allele, it is absent from the post-bottleneck population. This can happen by random sampling.
11. Why can genetic drift make two isolated populations diverge even if they live in similar environments?
Explanation. When populations are isolated, chance changes in each population can accumulate independently, causing divergence without different selection pressures.
12. Which conservation strategy would most directly reduce future genetic drift in a small endangered population?
Explanation. Larger effective population size reduces random sampling effects, and gene flow can add variation that small isolated populations may lose.
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FAQ
What is genetic drift in AP Biology?
Genetic drift is random change in allele frequencies caused by chance sampling of which individuals survive or reproduce, with the strongest effects in small populations.
How are bottlenecks and founder effects related?
Both are forms of genetic drift. A bottleneck happens when an existing population is sharply reduced, while a founder effect happens when a new population begins from a small sample.
Does genetic drift always make populations better adapted?
No. Genetic drift is random with respect to fitness, so it can remove useful alleles, fix neutral or harmful alleles, or reduce genetic variation by chance.