PCB 4674 | PCB4674 Exam 4: Evolution - Florida
State University Updated and Latest Questions and
Correct Answers with Rationale
1. Which mechanism of evolutionary change is most specifically addressed by the study of
‘evo-devo’?
A. Changes in the frequency of alleles due to genetic drift.
B. The calculation of molecular clock rates using mitochondrial DNA.
C. The impact of horizontal gene transfer in prokaryotic populations.
D. Modifications in the spatial and temporal expression of developmental genes.
Correct Answer: D
Expert Explanation: Evolutionary developmental biology focuses on how changes in the
processes of development lead to morphological evolution. These changes often occur in
regulatory genes that control where and when other genes are turned on. This field
highlights the conservation of a genetic toolkit across diverse animal phyla. By altering the
timing or location of gene expression, evolution can produce vast phenotypic variation.
Understanding these developmental constraints is essential for explaining the origins of
complex biological structures.
2. In molecular evolution, what does a dN/dS ratio significantly greater than 1 typically
indicate?
A. The gene is undergoing strong purifying selection.
B. The gene is evolving neutrally without any selective pressure.
C. The gene has become a pseudogene and is no longer functional.
D. The gene is experiencing positive or diversifying selection.
Correct Answer: D
Expert Explanation: The dN/dS ratio compares non-synonymous substitutions to
synonymous substitutions in a coding sequence. When this ratio exceeds one, it suggests
that amino acid changes are being actively promoted by natural selection. This pattern is
common in genes involved in immune response or reproductive competition where
adaptation is rapid. Conversely, a ratio less than one implies that selection is acting to
preserve the existing protein structure. Scientists use this metric to identify genomic
regions that are undergoing adaptive evolution.
3. How do homeotic (Hox) genes determine the identity of body segments in bilaterian
animals?
A. By directly synthesizing the chitin required for exoskeletons.
,B. By increasing the rate of mutation during embryonic cleavage.
C. By acting as structural proteins within the cell membrane.
D. By encoding transcription factors that regulate downstream target genes.
Correct Answer: D
Expert Explanation: Hox genes are a group of related genes that control the body plan of
an embryo along the head-tail axis. They function by producing transcription factors which
bind to specific DNA sequences to control gene batteries. This hierarchical control ensures
that organs like wings or legs develop in the correct anatomical locations. A mutation in a
Hox gene can result in dramatic homeotic transformations, such as legs growing where
antennae should be. Their high degree of conservation across species underscores their
fundamental role in animal architecture.
4. Which term describes the evolution of different phenotypic traits from a single genotype in
response to varying environmental conditions?
A. Phenotypic plasticity
B. Genetic canalization
C. Muller’s Ratchet
D. Homoplasy
Correct Answer: A
Expert Explanation: Phenotypic plasticity allows organisms to adapt their morphology or
behavior based on environmental cues without changing their DNA sequence. This
mechanism provides a buffer against environmental variability and can lead to immediate
fitness benefits. For example, some aquatic invertebrates develop defensive spines only in
the presence of predator chemicals. While the capacity for plasticity is genetically
determined, the specific outcome depends on the external context. Over evolutionary time,
plastic responses can sometimes become genetically fixed through a process called genetic
assimilation.
5. Gene duplication is a major source of evolutionary novelty. What is ‘neofunctionalization’?
A. Both gene copies retain the original function perfectly.
B. Both copies accumulate mutations and eventually become pseudogenes.
C. One gene copy acquires a completely new and beneficial function.
D. The original function is split between the two duplicated copies.
Correct Answer: C
Expert Explanation: Following a gene duplication event, the redundant copy is often free
from the constraints of purifying selection. Neofunctionalization occurs when one of these
, copies accumulates mutations that give rise to a novel biological role. This process allows
for the expansion of gene families and the emergence of complex new traits. The other copy
typically maintains the ancestral function to ensure the organism’s survival. This
mechanism is considered a primary driver of genomic complexity and metabolic diversity
in eukaryotes.
6. The ‘Neutral Theory of Molecular Evolution’ suggests that most evolutionary changes at
the molecular level are caused by:
A. Intense natural selection favoring beneficial mutations.
B. Random genetic drift of alleles that are selectively neutral.
C. Environmental changes forcing immediate adaptation.
D. High rates of recombination in sexual populations.
Correct Answer: B
Expert Explanation: Motoo Kimura’s Neutral Theory proposes that the majority of
molecular variation within and between species is not due to selection. Instead, these
changes result from the random fixation of mutations that do not significantly affect fitness.
This theory provides a null model for molecular evolution and is the basis for the molecular
clock. It implies that the rate of molecular evolution can be relatively constant over long
periods. While adaptive evolution occurs, it is statistically less frequent at the nucleotide
level than neutral changes.
7. Which evolutionary ecology concept explains why organisms often face a trade-off
between offspring number and offspring size?
A. Kin selection
B. The Red Queen hypothesis
C. Life history theory
D. Competitive exclusion principle
Correct Answer: C
Expert Explanation: Life history theory examines how natural selection shapes the timing
and energy allocation of reproduction and growth. Since resources are finite, an organism
cannot maximize all fitness components simultaneously. Investing heavily in a large
number of offspring typically reduces the energy available for each individual offspring’s
development. This results in a fundamental trade-off that is influenced by environmental
stability and mortality rates. Evolution optimizes these strategies to maximize the total
number of surviving descendants in a given habitat.
8. Heterochrony refers to an evolutionary change in the timing or rate of developmental
events. What is ‘paedomorphosis’?
A. Retention of juvenile traits in the adult form of an organism.
State University Updated and Latest Questions and
Correct Answers with Rationale
1. Which mechanism of evolutionary change is most specifically addressed by the study of
‘evo-devo’?
A. Changes in the frequency of alleles due to genetic drift.
B. The calculation of molecular clock rates using mitochondrial DNA.
C. The impact of horizontal gene transfer in prokaryotic populations.
D. Modifications in the spatial and temporal expression of developmental genes.
Correct Answer: D
Expert Explanation: Evolutionary developmental biology focuses on how changes in the
processes of development lead to morphological evolution. These changes often occur in
regulatory genes that control where and when other genes are turned on. This field
highlights the conservation of a genetic toolkit across diverse animal phyla. By altering the
timing or location of gene expression, evolution can produce vast phenotypic variation.
Understanding these developmental constraints is essential for explaining the origins of
complex biological structures.
2. In molecular evolution, what does a dN/dS ratio significantly greater than 1 typically
indicate?
A. The gene is undergoing strong purifying selection.
B. The gene is evolving neutrally without any selective pressure.
C. The gene has become a pseudogene and is no longer functional.
D. The gene is experiencing positive or diversifying selection.
Correct Answer: D
Expert Explanation: The dN/dS ratio compares non-synonymous substitutions to
synonymous substitutions in a coding sequence. When this ratio exceeds one, it suggests
that amino acid changes are being actively promoted by natural selection. This pattern is
common in genes involved in immune response or reproductive competition where
adaptation is rapid. Conversely, a ratio less than one implies that selection is acting to
preserve the existing protein structure. Scientists use this metric to identify genomic
regions that are undergoing adaptive evolution.
3. How do homeotic (Hox) genes determine the identity of body segments in bilaterian
animals?
A. By directly synthesizing the chitin required for exoskeletons.
,B. By increasing the rate of mutation during embryonic cleavage.
C. By acting as structural proteins within the cell membrane.
D. By encoding transcription factors that regulate downstream target genes.
Correct Answer: D
Expert Explanation: Hox genes are a group of related genes that control the body plan of
an embryo along the head-tail axis. They function by producing transcription factors which
bind to specific DNA sequences to control gene batteries. This hierarchical control ensures
that organs like wings or legs develop in the correct anatomical locations. A mutation in a
Hox gene can result in dramatic homeotic transformations, such as legs growing where
antennae should be. Their high degree of conservation across species underscores their
fundamental role in animal architecture.
4. Which term describes the evolution of different phenotypic traits from a single genotype in
response to varying environmental conditions?
A. Phenotypic plasticity
B. Genetic canalization
C. Muller’s Ratchet
D. Homoplasy
Correct Answer: A
Expert Explanation: Phenotypic plasticity allows organisms to adapt their morphology or
behavior based on environmental cues without changing their DNA sequence. This
mechanism provides a buffer against environmental variability and can lead to immediate
fitness benefits. For example, some aquatic invertebrates develop defensive spines only in
the presence of predator chemicals. While the capacity for plasticity is genetically
determined, the specific outcome depends on the external context. Over evolutionary time,
plastic responses can sometimes become genetically fixed through a process called genetic
assimilation.
5. Gene duplication is a major source of evolutionary novelty. What is ‘neofunctionalization’?
A. Both gene copies retain the original function perfectly.
B. Both copies accumulate mutations and eventually become pseudogenes.
C. One gene copy acquires a completely new and beneficial function.
D. The original function is split between the two duplicated copies.
Correct Answer: C
Expert Explanation: Following a gene duplication event, the redundant copy is often free
from the constraints of purifying selection. Neofunctionalization occurs when one of these
, copies accumulates mutations that give rise to a novel biological role. This process allows
for the expansion of gene families and the emergence of complex new traits. The other copy
typically maintains the ancestral function to ensure the organism’s survival. This
mechanism is considered a primary driver of genomic complexity and metabolic diversity
in eukaryotes.
6. The ‘Neutral Theory of Molecular Evolution’ suggests that most evolutionary changes at
the molecular level are caused by:
A. Intense natural selection favoring beneficial mutations.
B. Random genetic drift of alleles that are selectively neutral.
C. Environmental changes forcing immediate adaptation.
D. High rates of recombination in sexual populations.
Correct Answer: B
Expert Explanation: Motoo Kimura’s Neutral Theory proposes that the majority of
molecular variation within and between species is not due to selection. Instead, these
changes result from the random fixation of mutations that do not significantly affect fitness.
This theory provides a null model for molecular evolution and is the basis for the molecular
clock. It implies that the rate of molecular evolution can be relatively constant over long
periods. While adaptive evolution occurs, it is statistically less frequent at the nucleotide
level than neutral changes.
7. Which evolutionary ecology concept explains why organisms often face a trade-off
between offspring number and offspring size?
A. Kin selection
B. The Red Queen hypothesis
C. Life history theory
D. Competitive exclusion principle
Correct Answer: C
Expert Explanation: Life history theory examines how natural selection shapes the timing
and energy allocation of reproduction and growth. Since resources are finite, an organism
cannot maximize all fitness components simultaneously. Investing heavily in a large
number of offspring typically reduces the energy available for each individual offspring’s
development. This results in a fundamental trade-off that is influenced by environmental
stability and mortality rates. Evolution optimizes these strategies to maximize the total
number of surviving descendants in a given habitat.
8. Heterochrony refers to an evolutionary change in the timing or rate of developmental
events. What is ‘paedomorphosis’?
A. Retention of juvenile traits in the adult form of an organism.
