ASU BIO 182 Exam 2 Actual Practice
Questions Complete Verified Solutions &
Preparation
SECTION 1: EVOLUTIONARY THEORY & NATURAL SELECTION (Questions
1-10)
Q1: A population of beetles varies in color from light brown to dark brown. Over several
generations in a forest with dark soil and predators that hunt by sight, the frequency of
dark brown beetles increases from 20% to 85%. This is most directly an example of:
A. Genetic drift altering allele frequencies randomly
B. Artificial selection by human intervention
C. Natural selection increasing frequency of a heritable trait that improves survival
D. Sexual selection based on mate choice
Correct Answer: C
Rationale: This scenario describes natural selection—differential survival and
reproduction due to a heritable trait (color) that provides a fitness advantage
(camouflage) in a specific environment. Genetic drift (A) is random, not directional.
Artificial selection (B) involves human choice. Sexual selection (D) involves mate
preference, not predator avoidance.
,Q2: Which of the following statements best distinguishes Lamarckian inheritance from
Darwinian evolution by natural selection?
A. Lamarck proposed that acquired characteristics are inherited; Darwin proposed that
variation exists and environmental pressures select for advantageous traits
B. Lamarck rejected the idea of evolution entirely; Darwin was the first to propose
evolutionary change
C. Lamarck focused on genetic mutations as the source of variation; Darwin focused on
natural selection acting on existing variation
D. Lamarck and Darwin held identical views on the mechanisms of evolutionary change
Correct Answer: A
Rationale: Lamarck incorrectly proposed that organisms could pass on characteristics
acquired during their lifetime (e.g., giraffes stretching necks). Darwin correctly identified
that variation exists in populations and that natural selection acts on this pre-existing
variation. Darwin did not know the genetic basis of variation (Mendel's work came later),
eliminating C. Both scientists accepted evolution, eliminating B. Their mechanisms were
fundamentally different, eliminating D.
Q3: In a population of birds, individuals with larger beaks can crack harder seeds, which
become more abundant during drought years. During wet years, smaller beaks are
favored because they allow more efficient handling of soft seeds. This pattern
represents:
A. Directional selection
B. Disruptive selection
, C. Stabilizing selection
D. Balancing selection
Correct Answer: D
Rationale: This describes balancing selection (specifically frequency-dependent or
fluctuating selection), where multiple phenotypes are maintained in the population
because environmental conditions vary. Directional selection (A) favors one extreme
consistently. Disruptive selection (B) favors both extremes simultaneously. Stabilizing
selection (C) favors intermediate phenotypes. The fluctuating environment maintains
both beak sizes, making D correct.
Q4: A biologist observes that a population of fish in a lake has remained unchanged in
average body size for 50 years despite environmental fluctuations. The most likely
explanation is:
A. Strong directional selection consistently favoring larger body size
B. Stabilizing selection maintaining an intermediate optimal body size
C. Complete absence of any selective pressures on body size
D. Genetic drift causing random fluctuations in body size genes
Correct Answer: B
Rationale: Stabilizing selection favors intermediate phenotypes and reduces variation,
maintaining a stable average over time. This commonly occurs when extreme sizes
have disadvantages (too small = predation risk, too large = food limitation). Directional
selection (A) would change the average. Complete absence of selection (C) is
biologically unrealistic. Genetic drift (D) causes random change, not stability.
Questions Complete Verified Solutions &
Preparation
SECTION 1: EVOLUTIONARY THEORY & NATURAL SELECTION (Questions
1-10)
Q1: A population of beetles varies in color from light brown to dark brown. Over several
generations in a forest with dark soil and predators that hunt by sight, the frequency of
dark brown beetles increases from 20% to 85%. This is most directly an example of:
A. Genetic drift altering allele frequencies randomly
B. Artificial selection by human intervention
C. Natural selection increasing frequency of a heritable trait that improves survival
D. Sexual selection based on mate choice
Correct Answer: C
Rationale: This scenario describes natural selection—differential survival and
reproduction due to a heritable trait (color) that provides a fitness advantage
(camouflage) in a specific environment. Genetic drift (A) is random, not directional.
Artificial selection (B) involves human choice. Sexual selection (D) involves mate
preference, not predator avoidance.
,Q2: Which of the following statements best distinguishes Lamarckian inheritance from
Darwinian evolution by natural selection?
A. Lamarck proposed that acquired characteristics are inherited; Darwin proposed that
variation exists and environmental pressures select for advantageous traits
B. Lamarck rejected the idea of evolution entirely; Darwin was the first to propose
evolutionary change
C. Lamarck focused on genetic mutations as the source of variation; Darwin focused on
natural selection acting on existing variation
D. Lamarck and Darwin held identical views on the mechanisms of evolutionary change
Correct Answer: A
Rationale: Lamarck incorrectly proposed that organisms could pass on characteristics
acquired during their lifetime (e.g., giraffes stretching necks). Darwin correctly identified
that variation exists in populations and that natural selection acts on this pre-existing
variation. Darwin did not know the genetic basis of variation (Mendel's work came later),
eliminating C. Both scientists accepted evolution, eliminating B. Their mechanisms were
fundamentally different, eliminating D.
Q3: In a population of birds, individuals with larger beaks can crack harder seeds, which
become more abundant during drought years. During wet years, smaller beaks are
favored because they allow more efficient handling of soft seeds. This pattern
represents:
A. Directional selection
B. Disruptive selection
, C. Stabilizing selection
D. Balancing selection
Correct Answer: D
Rationale: This describes balancing selection (specifically frequency-dependent or
fluctuating selection), where multiple phenotypes are maintained in the population
because environmental conditions vary. Directional selection (A) favors one extreme
consistently. Disruptive selection (B) favors both extremes simultaneously. Stabilizing
selection (C) favors intermediate phenotypes. The fluctuating environment maintains
both beak sizes, making D correct.
Q4: A biologist observes that a population of fish in a lake has remained unchanged in
average body size for 50 years despite environmental fluctuations. The most likely
explanation is:
A. Strong directional selection consistently favoring larger body size
B. Stabilizing selection maintaining an intermediate optimal body size
C. Complete absence of any selective pressures on body size
D. Genetic drift causing random fluctuations in body size genes
Correct Answer: B
Rationale: Stabilizing selection favors intermediate phenotypes and reduces variation,
maintaining a stable average over time. This commonly occurs when extreme sizes
have disadvantages (too small = predation risk, too large = food limitation). Directional
selection (A) would change the average. Complete absence of selection (C) is
biologically unrealistic. Genetic drift (D) causes random change, not stability.
