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18. Population Genetics — Practice Questions 2
This chapter explores how genetic variation and evolutionary forces affect allele frequencies, focusing on Hardy-Weinberg equilibrium, genetic drift, gene flow, and founder and bottleneck effects.
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(Multiple Choice — Click to Reveal Answer)
1. What term describes the sum total of all genetic information in a population?
(A) Genotype pool
(B) Phenotype pool
(C) Gene pool
(D) Allele bank
Answer
(C) — The gene pool refers to all the alleles present in a population.
2. Which scenario best illustrates gene flow?
(A) A mutation changes a DNA base in one individual's gamete
(B) Two populations of frogs interbreed after a dam is removed
(C) A new species evolves from a common ancestor
(D) A disease eliminates most individuals with a specific genotype
Answer
(B) — Gene flow occurs when individuals or gametes move between populations, introducing new alleles.
3. In a population of 200 individuals, 50 are homozygous recessive. What is the estimated value of q?
(A) 0.25
(B) 0.50
(C) 0.75
(D) 0.87
Answer
(B) — q² = 50/200 = 0.25 → q = √0.25 = 0.5.
4. What type of selection occurs when individuals with extreme phenotypes are selected against?
(A) Directional selection
(B) Stabilizing selection
(C) Disruptive selection
(D) Balancing selection
Answer
(B) — Stabilizing selection favors intermediate phenotypes, reducing variation.
5. Which of the following would violate the assumption of no selection in Hardy-Weinberg equilibrium?
(A) All individuals have equal fitness
(B) Some genotypes produce more offspring than others
(C) There is no gene flow
(D) Mating is random
Answer
(B) — Selection occurs when individuals with certain genotypes reproduce more successfully than others, violating the assumption.
6. Which condition would maintain Hardy-Weinberg equilibrium?
(A) Frequent mutation
(B) Small population
(C) No migration
(D) Natural selection
Answer
(C) — No migration (gene flow) is one of the required conditions for Hardy-Weinberg equilibrium.
7. What is the expected frequency of heterozygotes if p = 0.6 and q = 0.4?
(A) 0.24
(B) 0.48
(C) 0.16
(D) 0.36
Answer
(B) — 2pq = 2(0.6)(0.4) = 0.48.
8. Which of the following evolutionary forces increases genetic variation?
(A) Genetic drift
(B) Stabilizing selection
(C) Mutation
(D) Inbreeding
Answer
(C) — Mutation introduces new alleles, increasing genetic variation.
9. Which of the following describes a founder effect?
(A) A population recovers from a bottleneck
(B) A small group starts a new population with limited genetic variation
(C) A gene mutates and spreads quickly
(D) A population undergoes stabilizing selection
Answer
(B) — The founder effect happens when a few individuals colonize a new area and represent a limited gene pool.
10. Which statement best reflects the concept of genetic drift?
(A) Random changes in allele frequencies, especially in small populations
(B) Alleles that improve survival always increase
(C) Natural selection acts on all traits equally
(D) Dominant alleles become more common over time
Answer
(A) — Genetic drift is a random process that has more impact in small populations.
11. Which of the following is NOT a mechanism that changes allele frequencies?
(A) Genetic drift
(B) Mutation
(C) Random mating
(D) Gene flow
Answer
(C) — Random mating does not change allele frequencies and is a requirement for Hardy-Weinberg equilibrium.
12. What type of genetic drift occurs after a sharp reduction in population size?
(A) Founder effect
(B) Bottleneck effect
(C) Natural selection
(D) Sexual selection
Answer
(B) — Bottleneck effect reduces population size drastically, leading to reduced genetic diversity.
13. Which factor directly leads to increased homozygosity in a population?
(A) Outbreeding
(B) Mutation
(C) Inbreeding
(D) Gene flow
Answer
(C) — Inbreeding increases the frequency of homozygous genotypes by pairing similar alleles more often.
14. If q = 0.1 in a population, what percentage of individuals are expected to be homozygous recessive?
(A) 1%
(B) 10%
(C) 20%
(D) 90%
Answer
(A) — q² = (0.1)² = 0.01 or 1% of the population.
15. What does it mean if a population has reached Hardy-Weinberg equilibrium?
(A) Evolution is occurring
(B) Allele frequencies are changing rapidly
(C) Allele and genotype frequencies remain constant
(D) The population is declining
Answer
(C) — At Hardy-Weinberg equilibrium, allele and genotype frequencies do not change across generations.
16. Which of the following is an example of gene flow?
(A) A neutral mutation occurs in a gene
(B) A new trait is selected for over time
(C) Individuals migrate between populations and reproduce
(D) A founder effect reduces genetic diversity
Answer
(C) — Gene flow results from the movement of individuals and their alleles between populations.
17. What happens to recessive alleles under Hardy-Weinberg equilibrium?
(A) They are eliminated
(B) They increase rapidly
(C) Their frequency remains constant
(D) They mutate to dominant forms
Answer
(C) — Without selection or other forces, allele frequencies—including recessive ones—remain unchanged.
18. Which equation represents Hardy-Weinberg equilibrium?
(A) p² + 2pq + q² = 1
(B) p + q = 2
(C) p × q = 1
(D) p - q = 0
Answer
(A) — This equation describes genotype frequencies in Hardy-Weinberg equilibrium.
19. Which of the following would likely increase genetic variation in a population?
(A) Inbreeding
(B) Founder effect
(C) Mutation
(D) Genetic drift
Answer
(C) — Only mutation introduces new genetic material, increasing variation.
20. A population with p = 0.3 and q = 0.7 will have what frequency of heterozygotes?
(A) 0.91
(B) 0.49
(C) 0.42
(D) 0.21
Answer
(C) — 2pq = 2(0.3)(0.7) = 0.42.
21. Which of the following would likely reduce genetic variation?
(A) Gene flow
(B) Mutation
(C) Bottleneck event
(D) Random mating
Answer
(C) — Bottlenecks decrease population size and genetic variation due to random survival.
22. Why is a large population size important in maintaining Hardy-Weinberg equilibrium?
(A) It promotes mutation
(B) It minimizes selection pressure
(C) It reduces genetic drift
(D) It increases allele frequency
Answer
(C) — Large populations are less affected by random events, minimizing the impact of genetic drift.
23. What is the term for the percentage of individuals in a population carrying a particular allele?
(A) Genotype frequency
(B) Genetic drift
(C) Allele frequency
(D) Recombination rate
Answer
(C) — Allele frequency measures how common a specific allele is in the gene pool.
24. Which of these would cause allele frequencies to shift significantly over a short period?
(A) Bottleneck effect
(B) Random mating
(C) Large population size
(D) No mutation
Answer
(A) — A bottleneck causes a rapid change in allele frequencies due to population reduction and random survival.
25. What is the consequence of continued inbreeding over many generations?
(A) Increased genetic diversity
(B) Increased heterozygosity
(C) Increased expression of recessive traits
(D) Elimination of recessive alleles
Answer
(C) — Inbreeding increases homozygosity, making recessive traits more likely to be expressed.
26. A population is evolving if:
(A) Allele frequencies remain constant
(B) Mating is completely random
(C) There is a consistent change in allele frequencies over generations
(D) The population is in Hardy-Weinberg equilibrium
Answer
(C) — Evolution is defined as a change in allele frequencies in a population over time.
27. A scientist observes that individuals with heterozygous genotypes have a survival advantage in a population. What mechanism is most likely maintaining both alleles in the population?
(A) Bottleneck effect
(B) Gene flow
(C) Heterozygote advantage
(D) Founder effect
Answer
(C) — Heterozygote advantage preserves both alleles by giving heterozygotes higher fitness than either homozygote.
28. A gene in a population has two alleles, B and b. If 36% of individuals are homozygous recessive, what is the frequency of the dominant allele B?
(A) 0.6
(B) 0.4
(C) 0.2
(D) 0.8
Answer
(A) — q² = 0.36 → q = 0.6 → p = 1 - 0.6 = 0.4 (Check: this question actually asks for B, so it’s 0.4).
29. Which of the following would be considered a violation of Hardy-Weinberg equilibrium?
(A) No mutation
(B) Natural selection occurs
(C) Very large population
(D) Random mating
Answer
(B) — Natural selection changes allele frequencies and violates equilibrium assumptions.
30. In a population of 1,000 individuals, 160 are homozygous recessive for a particular gene. What is the frequency of the dominant allele?
(A) 0.2
(B) 0.4
(C) 0.6
(D) 0.8
Answer
(D) — q² = 160/1000 = 0.16 → q = 0.4 → p = 1 - 0.4 = 0.6
31. Which statement best explains why Hardy-Weinberg equilibrium is used as a null model in population genetics?
(A) It shows how alleles disappear from a population
(B) It predicts mutation rates
(C) It provides a baseline for detecting evolutionary change
(D) It proves that evolution does not occur
Answer
(C) — Deviations from Hardy-Weinberg equilibrium indicate that evolutionary forces are acting on the population.
32. Which of the following would most likely cause a population to shift away from Hardy-Weinberg proportions?
(A) Random mating
(B) Mutations that do not affect phenotype
(C) Immigration of individuals with different allele frequencies
(D) Large population size
Answer
(C) — Gene flow introduces new alleles, disrupting existing allele frequencies.
33. In a population with three genotypes (AA, Aa, and aa), the frequency of Aa is higher than expected under Hardy-Weinberg. What might this suggest?
(A) Natural selection favors homozygotes
(B) Nonrandom mating is occurring
(C) There may be a heterozygote advantage
(D) Genetic drift is eliminating variation
Answer
(C) — Excess heterozygosity often indicates that heterozygotes have greater fitness.
34. What would you expect in a population that recently experienced a bottleneck event?
(A) High levels of genetic variation
(B) Many new mutations
(C) Rapid return to Hardy-Weinberg equilibrium
(D) Reduced allele diversity
Answer
(D) — Bottlenecks drastically reduce genetic variation due to random loss of alleles.
35. In a population with allele frequencies p = 0.9 and q = 0.1, which genotype is expected to be the most frequent?
(A) Homozygous dominant
(B) Heterozygous
(C) Homozygous recessive
(D) All genotypes are equally common
Answer
(A) — p² = 0.81, so homozygous dominant genotype is the most common.
36. Explain how the bottleneck effect can lead to a decrease in genetic variation.
Answer
When a large population is drastically reduced in size due to a random event, many alleles may be lost simply by chance, resulting in decreased genetic variation among the survivors.
37. Why is mutation considered the ultimate source of genetic variation?
Answer
Mutations introduce new alleles into a population’s gene pool, providing the raw material upon which natural selection and other forces can act, driving evolution.
38. Describe one real-world example where gene flow has altered allele frequencies in a population.
Answer
Gene flow occurred when European and African populations interbred during migration events, introducing new alleles and changing genetic diversity in both populations.
39. What are the five conditions required for Hardy-Weinberg equilibrium?
Answer
1) No mutations, 2) Random mating, 3) No natural selection, 4) Extremely large population size, 5) No gene flow (migration).
40. How can natural selection disrupt Hardy-Weinberg equilibrium?
Answer
Natural selection changes allele frequencies by favoring individuals with traits that increase fitness, causing those alleles to become more common in the next generation.
41. Explain the concept of heterozygote advantage using sickle cell anemia as an example.
Answer
In regions with malaria, individuals with one sickle cell allele (heterozygotes) have resistance to malaria without suffering severe symptoms of sickle cell disease, so both alleles persist in the population.
42. How does random genetic drift differ from natural selection?
Answer
Genetic drift is random and affects allele frequencies by chance, especially in small populations, while natural selection is non-random and favors alleles that enhance survival and reproduction.
43. Why might a small population not conform to Hardy-Weinberg expectations?
Answer
In small populations, allele frequencies can change drastically due to random sampling effects (genetic drift), leading to deviations from expected Hardy-Weinberg proportions.
44. A population is observed to have more homozygous individuals than expected under Hardy-Weinberg equilibrium. What could explain this?
Answer
Nonrandom mating (e.g., inbreeding) or a recent bottleneck could cause excess homozygosity by increasing the likelihood that individuals inherit identical alleles from common ancestors.
45. How can gene flow introduce new traits into a population?
Answer
When individuals migrate into a population and successfully reproduce, they bring new alleles that may introduce new traits or increase variation within the gene pool.
46. How does the Hardy-Weinberg model help scientists identify when evolution is occurring?
Answer
By comparing observed genotype frequencies to those predicted by the model, scientists can detect deviations that suggest evolutionary forces like selection or drift are acting.
47. What happens to rare alleles in small populations affected by genetic drift?
Answer
Rare alleles may be lost entirely or become fixed purely by chance, even if they have no effect on fitness.
48. How can a mutation become common in a population?
Answer
If a mutation provides a selective advantage or becomes fixed by chance (especially in small populations), it can increase in frequency and spread through the population.
49. Why might allele frequencies remain constant even when genotype frequencies change?
Answer
Allele frequencies can remain stable under Hardy-Weinberg conditions even if the ratio of heterozygotes to homozygotes changes due to factors like nonrandom mating.
50. How does the founder effect impact evolutionary potential in a new population?
Answer
The limited genetic diversity in a founding population restricts the range of traits available for selection, potentially reducing adaptability and increasing the impact of genetic drift.