Which of the following types of genetic drift involves a dramatic shrinkage in population size followed by a rebound in the population size?

Question

BlackTom AI · Accepted Answer

A population bottleneck describes a sharp reduction in population size followed by a rebound, causing loss of genetic variation.

1. Relevant knowledge points and concepts
- Genetic drift: random changes in allele frequencies due to sampling error in finite populations. Drift is stronger when population size is small.
- Bottleneck effect: an extreme form of genetic drift where a large population is suddenly reduced to a small number (e.g., by natural disaster), then later recovers in numbers. The surviving gene pool may be unrepresentative of the original, so genetic diversity is decreased permanently or for many generations.
- Founder effect: also a form of drift, occurring when a small group establishes a new population; it reduces diversity but is caused by dispersal/founding, not a shrink-and-recover event in an existing population.
- Negative-frequency-dependent selection: a selective process in which rare phenotypes have a fitness advantage; this is selection, not drift.

2. Step-by-step reasoning
- The phrase “dramatic shrinkage in population size followed by a rebound” directly matches the definition of a bottleneck: population crash then recovery.
- Bottlenecks cause random sampling of alleles: survivors’ allele frequencies determine future population frequencies after rebound.

3. Example calculation with intermediate steps
- Suppose initial population = 100 individuals with allele A frequency p = 0.6 and allele B frequency q = 0.4.
- A bottleneck leaves only 5 survivors. If by chance survivors include 4 A and 1 B, new frequencies among survivors: p' = 4/5 = 0.8, q' = 1/5 = 0.2.
- If the population rebounds back to 100 individuals, the allele frequencies will remain near p' = 0.8 and q' = 0.2. B’s representation has dropped, showing loss of original diversity due to the bottleneck.

4. Why the correct answer is correct
- The bottleneck effect explicitly involves a crash and recovery in population size that amplifies drift and alters allele frequencies permanently or long-term. That matches the description in the question.

5. Why other options are incorrect
- Founder effect: reduces diversity but describes a small group starting a new population, not a dramatic shrinkage followed by rebound in the original population.
- Negative-frequency dependent selection: is an adaptive selection mechanism that maintains or promotes diversity based on rarity, not a random shrinkage-and-rebound event.
- “Both a and b” is wrong because only the bottleneck (a) matches the shrinkage-and-rebound scenario; founder effect (b) is different.

6. Conclusion
The correct answer is The bottleneck effect, which matches the provided answer.

Which of the following types of genetic drift involves a dramatic shrinkage in population size followed by a rebound in the population size?Single choice

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