PCB4674 Exam 2: Evolution 2026 – FSU
1. Which of the following is the primary source of new genetic variation in a
population?
A. Genetic drift
B. Natural selection
C. Mutation
D. Gene flow
Answer: C
Rationale: Mutation is the ultimate source of all new alleles and genetic variation upon
which other evolutionary forces act.
2. In a population in Hardy-Weinberg equilibrium, if the frequency of the
recessive allele (q) is 0.3, what is the frequency of the heterozygous genotype?
A. 0.49
B. 0.21
C. 0.09
D. 0.42
Answer: D
Rationale: The frequency of heterozygotes is 2pq. If q = 0.3, then p = 0.7. 2 * 0.7 * 0.3 =
0.42.
,3. Which mode of selection favors individuals at both extremes of a trait’s
distribution while selecting against intermediate phenotypes?
A. Stabilizing selection
B. Directional selection
C. Disruptive selection
D. Negative frequency-dependent selection
Answer: C
Rationale: Disruptive selection favors the extremes and can lead to a bimodal distribution
of traits.
4. Genetic drift has the strongest effect on evolution in which type of
population?
A. Large, panmictic populations
B. Populations with high mutation rates
C. Populations undergoing intense sexual selection
D. Small, isolated populations
Answer: D
Rationale: Genetic drift is a stochastic process that causes random changes in allele
frequencies, and its effects are much more pronounced in small populations.
5. A monophyletic group is defined as:
A. An ancestor and all of its descendants
B. An ancestor and some, but not all, of its descendants
C. A group of organisms with similar traits but different ancestors
D. The most recent common ancestor only
Answer: A
Rationale: A monophyletic group (or clade) includes the common ancestor and every
single descendant that has branched off from it.
, 6. Which of the following describes the Biological Species Concept?
A. Species are defined by their ecological niche.
B. Species are defined by shared morphological characteristics.
C. Species are defined as the smallest monophyletic group on a phylogenetic tree.
D. Species are groups of interbreeding natural populations that are reproductively isolated from other such
groups.
Answer: D
Rationale: Ernst Mayr’s Biological Species Concept emphasizes reproductive isolation as
the key to defining species boundaries.
7. What is the term for a shared derived character state that defines a clade?
A. Symplesiomorphy
B. Autapomorphy
C. Homoplasy
D. Synapomorphy
Answer: D
Rationale: A synapomorphy is a trait that is unique to a specific clade and its common
ancestor, distinguishing it from other groups.
8. Which mechanism of evolution is most likely to reduce genetic differences
between two populations?
A. Natural selection
B. Mutation
C. Genetic drift
D. Gene flow
Answer: D
Rationale: Gene flow (migration) moves alleles between populations, making their gene
pools more similar over time.
1. Which of the following is the primary source of new genetic variation in a
population?
A. Genetic drift
B. Natural selection
C. Mutation
D. Gene flow
Answer: C
Rationale: Mutation is the ultimate source of all new alleles and genetic variation upon
which other evolutionary forces act.
2. In a population in Hardy-Weinberg equilibrium, if the frequency of the
recessive allele (q) is 0.3, what is the frequency of the heterozygous genotype?
A. 0.49
B. 0.21
C. 0.09
D. 0.42
Answer: D
Rationale: The frequency of heterozygotes is 2pq. If q = 0.3, then p = 0.7. 2 * 0.7 * 0.3 =
0.42.
,3. Which mode of selection favors individuals at both extremes of a trait’s
distribution while selecting against intermediate phenotypes?
A. Stabilizing selection
B. Directional selection
C. Disruptive selection
D. Negative frequency-dependent selection
Answer: C
Rationale: Disruptive selection favors the extremes and can lead to a bimodal distribution
of traits.
4. Genetic drift has the strongest effect on evolution in which type of
population?
A. Large, panmictic populations
B. Populations with high mutation rates
C. Populations undergoing intense sexual selection
D. Small, isolated populations
Answer: D
Rationale: Genetic drift is a stochastic process that causes random changes in allele
frequencies, and its effects are much more pronounced in small populations.
5. A monophyletic group is defined as:
A. An ancestor and all of its descendants
B. An ancestor and some, but not all, of its descendants
C. A group of organisms with similar traits but different ancestors
D. The most recent common ancestor only
Answer: A
Rationale: A monophyletic group (or clade) includes the common ancestor and every
single descendant that has branched off from it.
, 6. Which of the following describes the Biological Species Concept?
A. Species are defined by their ecological niche.
B. Species are defined by shared morphological characteristics.
C. Species are defined as the smallest monophyletic group on a phylogenetic tree.
D. Species are groups of interbreeding natural populations that are reproductively isolated from other such
groups.
Answer: D
Rationale: Ernst Mayr’s Biological Species Concept emphasizes reproductive isolation as
the key to defining species boundaries.
7. What is the term for a shared derived character state that defines a clade?
A. Symplesiomorphy
B. Autapomorphy
C. Homoplasy
D. Synapomorphy
Answer: D
Rationale: A synapomorphy is a trait that is unique to a specific clade and its common
ancestor, distinguishing it from other groups.
8. Which mechanism of evolution is most likely to reduce genetic differences
between two populations?
A. Natural selection
B. Mutation
C. Genetic drift
D. Gene flow
Answer: D
Rationale: Gene flow (migration) moves alleles between populations, making their gene
pools more similar over time.
