BIO111 Exam 4 Actual Exam V2 | BIO111 General Biology (BIO111
Exam 4) | UCLA
1. Which of the following best describes the process of natural selection?
A. Individual organisms change their genetic makeup in response to environmental
pressure.
B. Organisms with traits well-suited to their environment survive and reproduce at higher
rates.
C. The environment causes mutations to occur so that organisms can survive better.
D. Evolution occurs because organisms strive to become more complex over time.
Answer: B
Rationale: Natural selection is based on the differential reproductive success of individuals
with heritable traits. It requires pre-existing genetic variation within a population to act
upon. Over generations, this leads to an increase in the frequency of advantageous alleles.
2. In a population at Hardy-Weinberg equilibrium, what does the term ‘2pq’ represent?
A. The frequency of the dominant allele.
B. The frequency of the homozygous recessive genotype.
C. The frequency of the heterozygous genotype.
D. The total number of individuals in the population.
Answer: C
Rationale: The Hardy-Weinberg equation p^2 + 2pq + q^2 = 1 describes genotype
frequencies in a non-evolving population. Here, p and q represent allele frequencies, while
2pq specifically denotes the proportion of heterozygotes. This mathematical model serves
as a null hypothesis for detecting evolutionary change.
3. Which evolutionary mechanism is most likely to lead to a loss of genetic variation in small,
isolated populations?
A. Gene flow
B. Natural selection
C. Random mating
D. Genetic drift
Answer: D
,Rationale: Genetic drift refers to random fluctuations in allele frequencies that occur by
chance rather than selection. In small populations, these chance events can lead to the
permanent loss of alleles or the fixation of others. This process reduces the overall genetic
diversity of the group over time.
4. A massive earthquake reduces a population of snails to just ten individuals, who then
rebuild the population. This is an example of:
A. Bottleneck effect
B. Disruptive selection
C. Founder effect
D. Gene flow
Answer: A
Rationale: A bottleneck effect occurs when a sudden environmental change drastically
reduces the population size. The resulting gene pool is usually a limited and non-
representative sample of the original population’s genetics. As the population regrows, it
may exhibit significantly different allele frequencies than the ancestral group.
5. According to the biological species concept, a species is defined as a group of organisms
that:
A. Can interbreed and produce viable, fertile offspring.
B. Share a common ancestor in the fossil record.
C. Inhabit the same ecological niche.
D. Have identical morphological characteristics.
Answer: A
Rationale: The biological species concept emphasizes reproductive isolation as the
primary criterion for defining species. It focuses on the potential for gene flow between
populations rather than physical appearance. However, this definition is difficult to apply
to asexual organisms or extinct species found in fossils.
6. Which of the following is an example of a pre-zygotic reproductive barrier?
A. Hybrid breakdown
B. Hybrid sterility
C. Temporal isolation
D. Reduced hybrid viability
Answer: C
, Rationale: Pre-zygotic barriers prevent fertilization from occurring between different
species. Temporal isolation happens when species breed at different times of the day,
season, or year. This prevents the formation of a zygote, unlike post-zygotic barriers which
affect the hybrid offspring after birth.
7. In a phylogenetic tree, a group that includes an ancestral species and all of its descendants
is called a:
A. Monophyletic group
B. Polyphyletic group
C. Paraphyletic group
D. Outgroup
Answer: A
Rationale: A monophyletic group, or clade, consists of an ancestor and every single
descendant stemming from it. This classification reflects true evolutionary relationships
based on shared derived characters. Paraphyletic and polyphyletic groups are considered
incomplete or inaccurate in modern cladistics.
8. Which type of selection favors individuals at both extremes of a phenotypic range over
intermediate phenotypes?
A. Stabilizing selection
B. Disruptive selection
C. Directional selection
D. Sexual selection
Answer: B
Rationale: Disruptive selection occurs when environmental conditions favor individuals
with extreme traits over those with average traits. This can lead to a bimodal distribution
of phenotypes within the population. Over long periods, this type of selection may facilitate
speciation if the groups become reproductively isolated.
9. The presence of wings in both birds and bats is an example of:
A. Homologous structures
B. Vestigial structures
C. Analogous structures
D. Derived characters
Answer: C
Exam 4) | UCLA
1. Which of the following best describes the process of natural selection?
A. Individual organisms change their genetic makeup in response to environmental
pressure.
B. Organisms with traits well-suited to their environment survive and reproduce at higher
rates.
C. The environment causes mutations to occur so that organisms can survive better.
D. Evolution occurs because organisms strive to become more complex over time.
Answer: B
Rationale: Natural selection is based on the differential reproductive success of individuals
with heritable traits. It requires pre-existing genetic variation within a population to act
upon. Over generations, this leads to an increase in the frequency of advantageous alleles.
2. In a population at Hardy-Weinberg equilibrium, what does the term ‘2pq’ represent?
A. The frequency of the dominant allele.
B. The frequency of the homozygous recessive genotype.
C. The frequency of the heterozygous genotype.
D. The total number of individuals in the population.
Answer: C
Rationale: The Hardy-Weinberg equation p^2 + 2pq + q^2 = 1 describes genotype
frequencies in a non-evolving population. Here, p and q represent allele frequencies, while
2pq specifically denotes the proportion of heterozygotes. This mathematical model serves
as a null hypothesis for detecting evolutionary change.
3. Which evolutionary mechanism is most likely to lead to a loss of genetic variation in small,
isolated populations?
A. Gene flow
B. Natural selection
C. Random mating
D. Genetic drift
Answer: D
,Rationale: Genetic drift refers to random fluctuations in allele frequencies that occur by
chance rather than selection. In small populations, these chance events can lead to the
permanent loss of alleles or the fixation of others. This process reduces the overall genetic
diversity of the group over time.
4. A massive earthquake reduces a population of snails to just ten individuals, who then
rebuild the population. This is an example of:
A. Bottleneck effect
B. Disruptive selection
C. Founder effect
D. Gene flow
Answer: A
Rationale: A bottleneck effect occurs when a sudden environmental change drastically
reduces the population size. The resulting gene pool is usually a limited and non-
representative sample of the original population’s genetics. As the population regrows, it
may exhibit significantly different allele frequencies than the ancestral group.
5. According to the biological species concept, a species is defined as a group of organisms
that:
A. Can interbreed and produce viable, fertile offspring.
B. Share a common ancestor in the fossil record.
C. Inhabit the same ecological niche.
D. Have identical morphological characteristics.
Answer: A
Rationale: The biological species concept emphasizes reproductive isolation as the
primary criterion for defining species. It focuses on the potential for gene flow between
populations rather than physical appearance. However, this definition is difficult to apply
to asexual organisms or extinct species found in fossils.
6. Which of the following is an example of a pre-zygotic reproductive barrier?
A. Hybrid breakdown
B. Hybrid sterility
C. Temporal isolation
D. Reduced hybrid viability
Answer: C
, Rationale: Pre-zygotic barriers prevent fertilization from occurring between different
species. Temporal isolation happens when species breed at different times of the day,
season, or year. This prevents the formation of a zygote, unlike post-zygotic barriers which
affect the hybrid offspring after birth.
7. In a phylogenetic tree, a group that includes an ancestral species and all of its descendants
is called a:
A. Monophyletic group
B. Polyphyletic group
C. Paraphyletic group
D. Outgroup
Answer: A
Rationale: A monophyletic group, or clade, consists of an ancestor and every single
descendant stemming from it. This classification reflects true evolutionary relationships
based on shared derived characters. Paraphyletic and polyphyletic groups are considered
incomplete or inaccurate in modern cladistics.
8. Which type of selection favors individuals at both extremes of a phenotypic range over
intermediate phenotypes?
A. Stabilizing selection
B. Disruptive selection
C. Directional selection
D. Sexual selection
Answer: B
Rationale: Disruptive selection occurs when environmental conditions favor individuals
with extreme traits over those with average traits. This can lead to a bimodal distribution
of phenotypes within the population. Over long periods, this type of selection may facilitate
speciation if the groups become reproductively isolated.
9. The presence of wings in both birds and bats is an example of:
A. Homologous structures
B. Vestigial structures
C. Analogous structures
D. Derived characters
Answer: C
