Rucete ✏ AP Biology In a Nutshell
18. Population Genetics — Practice Questions
This chapter explores the mechanisms that drive genetic variation and allele frequency changes in populations, including Hardy-Weinberg equilibrium, genetic drift, gene flow, and selection.
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(Multiple Choice — Click to Reveal Answer)
1. In which type of population is genetic drift most likely to cause significant allele frequency changes?
(A) Large populations
(B) Small populations
(C) Populations under strong selection
(D) Populations in Hardy-Weinberg equilibrium
Answer
(B) — Genetic drift is more impactful in small populations where random events can drastically alter allele frequencies.
2. The transfer of alleles from one population to another due to the movement of individuals is known as:
(A) Genetic drift
(B) Gene flow
(C) Bottleneck effect
(D) Mutation
Answer
(B) — Gene flow involves the introduction or removal of alleles due to migration, altering allele frequencies in populations.
3. In a Hardy-Weinberg population, 49% of individuals show the recessive phenotype. What is the frequency of the dominant allele?
(A) 0.3
(B) 0.5
(C) 0.7
(D) 0.9
Answer
(C) — q² = 0.49 → q = 0.7 → p = 1 - 0.7 = 0.3; therefore, the frequency of the dominant allele p is 0.3.
4. Which of the following is a condition required for Hardy-Weinberg equilibrium?
(A) Nonrandom mating
(B) Mutations
(C) No selection
(D) Small population size
Answer
(C) — For Hardy-Weinberg equilibrium, no natural selection should occur so that all alleles have equal reproductive success.
5. What happens to the genetic diversity of a population after a bottleneck event?
(A) It increases
(B) It stays the same
(C) It decreases
(D) It becomes unpredictable
Answer
(C) — Bottleneck events drastically reduce population size, causing a loss of genetic diversity due to random survival.
6. Which of the following best describes a population in Hardy-Weinberg equilibrium?
(A) A population experiencing frequent mutations
(B) A population evolving rapidly
(C) A population with constant allele frequencies over generations
(D) A population undergoing directional selection
Answer
(C) — Hardy-Weinberg equilibrium means allele and genotype frequencies remain constant from generation to generation.
7. Which evolutionary force involves the random change in allele frequencies from one generation to the next?
(A) Gene flow
(B) Natural selection
(C) Mutation
(D) Genetic drift
Answer
(D) — Genetic drift is random and most influential in small populations.
8. If two populations have different allele frequencies and individuals from one migrate to the other, what will most likely happen?
(A) The allele frequencies will diverge further
(B) The two populations will become genetically identical
(C) Genetic variation will decrease
(D) The populations will become more genetically similar
Answer
(D) — Gene flow tends to homogenize populations, making them more genetically similar.
9. What is the effect of inbreeding on a population?
(A) It increases heterozygosity
(B) It decreases homozygosity
(C) It increases homozygosity
(D) It promotes gene flow
Answer
(C) — Inbreeding increases the chance of homozygosity and expression of recessive traits.
10. A sudden flood wipes out most of a population, leaving only a few individuals. What is this called?
(A) Founder effect
(B) Gene flow
(C) Bottleneck effect
(D) Disruptive selection
Answer
(C) — A bottleneck effect occurs when a population undergoes a severe size reduction, reducing genetic diversity.
11. What does the Hardy-Weinberg equation calculate?
(A) Growth rate
(B) Population size
(C) Allele and genotype frequencies
(D) Mutation rates
Answer
(C) — The Hardy-Weinberg equation is used to estimate allele and genotype frequencies under ideal conditions.
12. What is the primary source of all new genetic variation?
(A) Genetic drift
(B) Mutation
(C) Natural selection
(D) Sexual reproduction
Answer
(B) — Mutations are the original source of genetic variation that fuels evolution.
13. What does the p² term in the Hardy-Weinberg equation represent?
(A) Frequency of heterozygotes
(B) Frequency of recessive allele
(C) Frequency of homozygous dominant individuals
(D) Frequency of the dominant allele
Answer
(C) — p² represents the proportion of homozygous dominant individuals (AA).
14. Which event is most likely to increase genetic variation in a population?
(A) Bottleneck effect
(B) Nonrandom mating
(C) Mutation
(D) Stabilizing selection
Answer
(C) — Mutation introduces new alleles, increasing variation.
15. What does q² represent in the Hardy-Weinberg formula?
(A) Homozygous dominant individuals
(B) Homozygous recessive individuals
(C) Heterozygous individuals
(D) Total allele frequency
Answer
(B) — q² is the frequency of homozygous recessive individuals (aa).
16. Why is Hardy-Weinberg equilibrium rarely found in natural populations?
(A) Populations are always small
(B) Mutations happen constantly
(C) The assumptions of the model are rarely all met
(D) Natural selection only happens in labs
Answer
(C) — The five assumptions are rarely all present in nature, so true equilibrium is uncommon.
17. Which of the following is NOT an assumption of Hardy-Weinberg equilibrium?
(A) No mutations
(B) Random mating
(C) Small population size
(D) No natural selection
Answer
(C) — Large population size is an assumption; small populations are more subject to drift.
18. What is the effect of gene flow on isolated populations?
(A) Increases reproductive isolation
(B) Increases genetic variation
(C) Eliminates genetic drift
(D) Decreases mutation rates
Answer
(B) — Gene flow adds new alleles, increasing diversity in isolated populations.
19. What is true if a population's allele frequencies are changing over time?
(A) The population is in equilibrium
(B) Evolution is not occurring
(C) Evolution is occurring
(D) Gene flow is absent
Answer
(C) — Evolution is defined as a change in allele frequencies over generations.
20. Which situation is most likely to result in the founder effect?
(A) A disease wipes out most of a population
(B) A few individuals start a new colony in isolation
(C) A mutation occurs in one organism
(D) Two populations merge
Answer
(B) — The founder effect occurs when a few individuals establish a new population, carrying only a subset of genetic variation.
21. In a population with two alleles, A and a, if p = 0.6, what is q?
(A) 0.4
(B) 0.6
(C) 1.2
(D) 0.36
Answer
(A) — p + q = 1 → q = 1 - 0.6 = 0.4.
22. What does 2pq represent in the Hardy-Weinberg equation?
(A) Homozygous dominant individuals
(B) Homozygous recessive individuals
(C) Heterozygous individuals
(D) Mutated individuals
Answer
(C) — 2pq is the frequency of heterozygous genotype (Aa).
23. Which factor does NOT cause allele frequency change in populations?
(A) Mutation
(B) Random mating
(C) Genetic drift
(D) Natural selection
Answer
(B) — Random mating does not change allele frequencies; it maintains them under Hardy-Weinberg equilibrium.
24. A population has p = 0.7. What is the frequency of the heterozygous genotype under Hardy-Weinberg conditions?
(A) 0.21
(B) 0.49
(C) 0.42
(D) 0.91
Answer
(C) — 2pq = 2(0.7)(0.3) = 0.42.
25. What term describes the proportion of all copies of a gene that is made up of a specific allele?
(A) Phenotype frequency
(B) Genotype frequency
(C) Allele frequency
(D) Heterozygosity
Answer
(C) — Allele frequency measures how common an allele is in the population’s gene pool.
26. A small group of birds colonizes a remote island. Over time, their allele frequencies differ significantly from the original population. What mechanism most likely explains this change?
(A) Gene flow
(B) Founder effect
(C) Natural selection
(D) Mutation
Answer
(B) — The founder effect occurs when a small group starts a new population with a limited gene pool.
27. In a population in Hardy-Weinberg equilibrium, p = 0.2. What is the expected frequency of heterozygous individuals?
(A) 0.16
(B) 0.32
(C) 0.64
(D) 0.80
Answer
(B) — 2pq = 2(0.2)(0.8) = 0.32.
28. Which of the following best explains why genetic drift can lead to the fixation of harmful alleles in a small population?
(A) Harmful alleles become dominant
(B) Random chance can cause alleles to become more common regardless of effect
(C) Selection always favors harmful traits
(D) Gene flow increases heterozygosity
Answer
(B) — In small populations, random fluctuations can allow even harmful alleles to become fixed by chance.
29. Which of the following scenarios would violate the Hardy-Weinberg assumption of random mating?
(A) Individuals choose mates based on color
(B) Mutations occur at low rates
(C) A disease removes part of the population
(D) The population is large
Answer
(A) — Nonrandom mating, such as mate choice based on phenotype, violates Hardy-Weinberg equilibrium.
30. If p = 0.5 in a population, which of the following statements is true?
(A) q = 0.25
(B) The frequency of heterozygotes is 0.5
(C) The frequency of homozygous recessive individuals is 0.5
(D) The allele frequencies are not in equilibrium
Answer
(B) — If p = 0.5, then q = 0.5, and 2pq = 2(0.5)(0.5) = 0.5.
31. A population’s genetic variation decreases significantly after a natural disaster. What evolutionary force is this an example of?
(A) Mutation
(B) Bottleneck effect
(C) Gene flow
(D) Sexual selection
Answer
(B) — The bottleneck effect reduces genetic variation due to random survival following a sharp population decline.
32. What is one consequence of a population not being in Hardy-Weinberg equilibrium?
(A) Allele frequencies remain unchanged
(B) No evolution occurs
(C) Evolution is occurring
(D) The population is becoming larger
Answer
(C) — A deviation from Hardy-Weinberg equilibrium indicates that at least one evolutionary force is acting on the population.
33. If a population has more heterozygotes than predicted under Hardy-Weinberg equilibrium, which force may be acting?
(A) Inbreeding
(B) Disruptive selection
(C) Stabilizing selection
(D) Heterozygote advantage
Answer
(D) — Heterozygote advantage can maintain higher levels of heterozygosity than expected under Hardy-Weinberg equilibrium.
34. Which best describes the effect of directional selection on allele frequencies over time?
(A) Maintains both alleles equally
(B) Increases frequency of both extremes
(C) Shifts the population toward one allele
(D) Removes genetic variation entirely
Answer
(C) — Directional selection increases the frequency of one allele that confers a fitness advantage.
35. In a large, randomly mating population, which of the following will maintain Hardy-Weinberg equilibrium?
(A) Strong natural selection
(B) No gene flow
(C) Mutations occurring at high rates
(D) Small population size
Answer
(B) — Lack of gene flow helps maintain equilibrium, as does the absence of other evolutionary forces.
36. Explain how gene flow can affect the genetic structure of two neighboring populations.
Answer
Gene flow introduces new alleles into a population and reduces genetic differences between populations, making them more genetically similar over time.
37. How does a population bottleneck increase the risk of genetic disorders?
Answer
Bottlenecks drastically reduce genetic diversity and can increase the frequency of harmful alleles by chance, elevating the risk of genetic disorders.
38. Describe how natural selection can alter allele frequencies in a population.
Answer
Natural selection favors alleles that increase fitness, causing those alleles to become more common in the population over generations.
39. Why does nonrandom mating violate Hardy-Weinberg equilibrium?
Answer
Nonrandom mating alters genotype frequencies by favoring specific combinations of alleles, disrupting the expected Hardy-Weinberg proportions.
40. How does the founder effect differ from the bottleneck effect?
Answer
The founder effect occurs when a new population is started by a few individuals, while a bottleneck is a reduction in existing population size; both result in reduced genetic variation.
41. What does it mean if a population is in Hardy-Weinberg equilibrium?
Answer
It means allele and genotype frequencies are stable over generations and no evolutionary forces are acting on the population.
42. Why is mutation necessary for evolution, even though most mutations are neutral or harmful?
Answer
Mutation is the source of all new genetic variation; even if most mutations are neutral or harmful, beneficial ones provide material for natural selection to act on.
43. How can stabilizing selection influence genetic diversity in a population?
Answer
Stabilizing selection favors intermediate traits and reduces variation by eliminating extreme phenotypes, thus narrowing the gene pool.
44. Describe the significance of the Hardy-Weinberg equation in population genetics.
Answer
The Hardy-Weinberg equation provides a baseline model to determine whether a population is evolving by comparing observed and expected genotype frequencies.
45. Explain why small populations are more susceptible to genetic drift.
Answer
In small populations, random events have a larger impact on allele frequencies, making genetic drift more likely to cause significant changes or fixations.
46. What is heterozygote advantage, and how does it maintain genetic diversity?
Answer
Heterozygote advantage occurs when heterozygous individuals have higher fitness than either homozygote, preserving both alleles in the population.
47. How can a deviation from Hardy-Weinberg proportions indicate that evolution is occurring?
Answer
If observed genotype frequencies differ from those predicted by Hardy-Weinberg, it suggests that factors like selection, drift, or gene flow are acting, indicating evolution.
48. Describe how natural disasters can influence genetic diversity through evolutionary mechanisms.
Answer
Natural disasters can cause bottlenecks, randomly eliminating individuals and reducing genetic diversity, potentially changing allele frequencies dramatically by chance.
49. What role does random mating play in maintaining Hardy-Weinberg equilibrium?
Answer
Random mating ensures allele combinations occur by chance, preserving expected genotype frequencies and preventing selection for specific traits.
50. Explain the relationship between allele frequency and genotype frequency in the Hardy-Weinberg model.
Answer
Allele frequencies (p and q) determine genotype frequencies (p², 2pq, q²) under the model’s assumptions; changes in allele frequencies shift genotype proportions.