PCB 4674 | PCB4674 Exam 3: Evolution - Florida
State University Updated and Latest Questions and
Correct Answers with Rationale
1. Which of the following best defines a monophyletic group in a phylogenetic tree?
A. A group that includes a common ancestor and all of its descendants.
B. A group consisting of multiple unrelated lineages without a common ancestor.
C. A group consisting of an ancestor and some of its descendants.
D. A group of species that share similar morphological traits regardless of ancestry.
Correct Answer: A
Expert Explanation: A monophyletic group, also known as a clade, is defined by sharing a
single common ancestor and all descendants of that ancestor. This classification is the
standard for modern evolutionary biology because it reflects true evolutionary history.
Paraphyletic groups are considered incomplete because they exclude certain descendants
of a common ancestor. Polyphyletic groups are avoided because they include taxa with
different ancestors based on convergent traits. Understanding these distinctions is critical
for accurately reading and interpreting cladograms.
2. In the context of allopatric speciation, what is the primary difference between vicariance
and dispersal?
A. Vicariance occurs within the same geographic area, whereas dispersal requires a large
physical distance.
B. Vicariance involves a physical barrier dividing a population, while dispersal involves
individuals moving to a new area.
C. Dispersal leads to genetic drift, while vicariance only involves natural selection
mechanisms.
D. Vicariance is a form of sympatric speciation, while dispersal is exclusively allopatric.
Correct Answer: B
Expert Explanation: Vicariance occurs when a pre-existing population is split by a newly
formed physical barrier like a mountain range or river. Dispersal happens when a subset of
a population migrates across an existing barrier to colonize a new habitat. Both processes
lead to geographic isolation, which is the hallmark of allopatric speciation. Genetic
divergence follows this isolation as populations adapt to different environments or
experience drift. Differentiating these two mechanisms helps evolutionary biologists
determine the historical biogeography of a species.
,3. Which reproductive isolating mechanism occurs when two species of frogs breed in the
same pond but at different times of the year?
A. Habitat isolation
B. Temporal isolation
C. Behavioral isolation
D. Mechanical isolation
Correct Answer: B
Expert Explanation: Temporal isolation is a prezygotic barrier where species cannot
interbreed because they mate at different times. This can include differences in time of day,
season, or even spanning several years. In this specific scenario, the frogs share a habitat
but are separated by their reproductive calendars. Because no zygote is formed, this
mechanism prevents the waste of metabolic energy on non-viable offspring. It is a common
driver of speciation in sympatric populations that occupy the same ecological niche.
4. On a phylogenetic tree, what does a node represent?
A. The most recent common ancestor of the descendant lineages.
B. The current evolutionary status of a living species.
C. The accumulation of mutations over a specific period of time.
D. The extinction of a specific lineage.
Correct Answer: A
Expert Explanation: Nodes are the branching points on a phylogenetic tree that signify a
speciation event. Each node represents the most recent common ancestor shared by the
lineages that stem from it. This point indicates where one ancestral lineage split into two or
more distinct descendant paths. By analyzing nodes, researchers can determine the relative
timing of evolutionary divergence between taxa. It serves as the fundamental unit for
calculating relatedness and building nested hierarchies of life.
5. What is the primary driver of adaptive radiation, such as that seen in Darwin’s finches?
A. A high rate of mutation across the entire genome.
B. Consistent environmental stability over millions of years.
C. A lack of natural selection allowing all variations to survive.
D. Ecological opportunity provided by new or vacant niches.
Correct Answer: D
Expert Explanation: Adaptive radiation occurs when a single ancestral lineage rapidly
diversifies into a wide variety of forms. This process is typically triggered by ecological
opportunity, such as the colonization of an island chain or the aftermath of a mass
, extinction. New environments provide diverse resources that select for specialized traits in
different sub-populations. Darwin’s finches are a classic example, where beak shapes
evolved to exploit different food sources on the Galápagos. This rapid diversification leads
to the creation of many new species in a relatively short geological timeframe.
6. The shift of Rhagoletis pomonella flies from hawthorn to apple trees is an example of
which speciation type?
A. Vicariant speciation
B. Allopatric speciation
C. Peripatric speciation
D. Sympatric speciation
Correct Answer: D
Expert Explanation: Sympatric speciation occurs when new species evolve from a single
ancestral species while inhabiting the same geographic region. In the case of Rhagoletis
pomonella, the introduction of apple trees created a new niche that some flies began to
exploit. Because apples and hawthorns fruit at different times, the flies became temporally
and behaviorally isolated. This host-plant preference led to reduced gene flow despite the
flies living in the same orchards. It demonstrates that physical barriers are not always
necessary for the process of speciation to occur.
7. A shared derived character that is unique to a particular clade is known as a:
A. Symplesiomorphy
B. Synapomorphy
C. Homoplasy
D. Autapomorphy
Correct Answer: B
Expert Explanation: Synapomorphies are traits that are shared by a group of organisms
and were inherited from their most recent common ancestor. These characters are
‘derived’ because they evolved in the ancestor and were passed down, distinguishing the
clade from other groups. They are the most useful features for reconstructing phylogenetic
relationships and identifying monophyletic groups. In contrast, symplesiomorphies are
shared ancestral traits that do not help define specific sub-clades. Correctly identifying
synapomorphies allows biologists to build more accurate and informative evolutionary
trees.
8. If a horse and a donkey mate to produce a sterile mule, this is an example of which type of
reproductive isolation?
A. Gametic isolation
B. Hybrid inviability
State University Updated and Latest Questions and
Correct Answers with Rationale
1. Which of the following best defines a monophyletic group in a phylogenetic tree?
A. A group that includes a common ancestor and all of its descendants.
B. A group consisting of multiple unrelated lineages without a common ancestor.
C. A group consisting of an ancestor and some of its descendants.
D. A group of species that share similar morphological traits regardless of ancestry.
Correct Answer: A
Expert Explanation: A monophyletic group, also known as a clade, is defined by sharing a
single common ancestor and all descendants of that ancestor. This classification is the
standard for modern evolutionary biology because it reflects true evolutionary history.
Paraphyletic groups are considered incomplete because they exclude certain descendants
of a common ancestor. Polyphyletic groups are avoided because they include taxa with
different ancestors based on convergent traits. Understanding these distinctions is critical
for accurately reading and interpreting cladograms.
2. In the context of allopatric speciation, what is the primary difference between vicariance
and dispersal?
A. Vicariance occurs within the same geographic area, whereas dispersal requires a large
physical distance.
B. Vicariance involves a physical barrier dividing a population, while dispersal involves
individuals moving to a new area.
C. Dispersal leads to genetic drift, while vicariance only involves natural selection
mechanisms.
D. Vicariance is a form of sympatric speciation, while dispersal is exclusively allopatric.
Correct Answer: B
Expert Explanation: Vicariance occurs when a pre-existing population is split by a newly
formed physical barrier like a mountain range or river. Dispersal happens when a subset of
a population migrates across an existing barrier to colonize a new habitat. Both processes
lead to geographic isolation, which is the hallmark of allopatric speciation. Genetic
divergence follows this isolation as populations adapt to different environments or
experience drift. Differentiating these two mechanisms helps evolutionary biologists
determine the historical biogeography of a species.
,3. Which reproductive isolating mechanism occurs when two species of frogs breed in the
same pond but at different times of the year?
A. Habitat isolation
B. Temporal isolation
C. Behavioral isolation
D. Mechanical isolation
Correct Answer: B
Expert Explanation: Temporal isolation is a prezygotic barrier where species cannot
interbreed because they mate at different times. This can include differences in time of day,
season, or even spanning several years. In this specific scenario, the frogs share a habitat
but are separated by their reproductive calendars. Because no zygote is formed, this
mechanism prevents the waste of metabolic energy on non-viable offspring. It is a common
driver of speciation in sympatric populations that occupy the same ecological niche.
4. On a phylogenetic tree, what does a node represent?
A. The most recent common ancestor of the descendant lineages.
B. The current evolutionary status of a living species.
C. The accumulation of mutations over a specific period of time.
D. The extinction of a specific lineage.
Correct Answer: A
Expert Explanation: Nodes are the branching points on a phylogenetic tree that signify a
speciation event. Each node represents the most recent common ancestor shared by the
lineages that stem from it. This point indicates where one ancestral lineage split into two or
more distinct descendant paths. By analyzing nodes, researchers can determine the relative
timing of evolutionary divergence between taxa. It serves as the fundamental unit for
calculating relatedness and building nested hierarchies of life.
5. What is the primary driver of adaptive radiation, such as that seen in Darwin’s finches?
A. A high rate of mutation across the entire genome.
B. Consistent environmental stability over millions of years.
C. A lack of natural selection allowing all variations to survive.
D. Ecological opportunity provided by new or vacant niches.
Correct Answer: D
Expert Explanation: Adaptive radiation occurs when a single ancestral lineage rapidly
diversifies into a wide variety of forms. This process is typically triggered by ecological
opportunity, such as the colonization of an island chain or the aftermath of a mass
, extinction. New environments provide diverse resources that select for specialized traits in
different sub-populations. Darwin’s finches are a classic example, where beak shapes
evolved to exploit different food sources on the Galápagos. This rapid diversification leads
to the creation of many new species in a relatively short geological timeframe.
6. The shift of Rhagoletis pomonella flies from hawthorn to apple trees is an example of
which speciation type?
A. Vicariant speciation
B. Allopatric speciation
C. Peripatric speciation
D. Sympatric speciation
Correct Answer: D
Expert Explanation: Sympatric speciation occurs when new species evolve from a single
ancestral species while inhabiting the same geographic region. In the case of Rhagoletis
pomonella, the introduction of apple trees created a new niche that some flies began to
exploit. Because apples and hawthorns fruit at different times, the flies became temporally
and behaviorally isolated. This host-plant preference led to reduced gene flow despite the
flies living in the same orchards. It demonstrates that physical barriers are not always
necessary for the process of speciation to occur.
7. A shared derived character that is unique to a particular clade is known as a:
A. Symplesiomorphy
B. Synapomorphy
C. Homoplasy
D. Autapomorphy
Correct Answer: B
Expert Explanation: Synapomorphies are traits that are shared by a group of organisms
and were inherited from their most recent common ancestor. These characters are
‘derived’ because they evolved in the ancestor and were passed down, distinguishing the
clade from other groups. They are the most useful features for reconstructing phylogenetic
relationships and identifying monophyletic groups. In contrast, symplesiomorphies are
shared ancestral traits that do not help define specific sub-clades. Correctly identifying
synapomorphies allows biologists to build more accurate and informative evolutionary
trees.
8. If a horse and a donkey mate to produce a sterile mule, this is an example of which type of
reproductive isolation?
A. Gametic isolation
B. Hybrid inviability
