Campbell’s Biology, 9e (Reece et al.)
Chapter 23 The Evolution of Populations
Concepts 23.1 and 23.4 are conceptually rich. Consequently, most of the questions in this chapter are
delegated to these two concepts. Concept 23.2 deals with the Hardy-Weinberg equilibrium, and many of
the application/analysis questions in this chapter are connected with Hardy-Weinberg math problems.
The series of four scenario/art questions on the sickle-cell allele is new to this chapter.
Multiple-Choice Questions
1) During an individual organism’s lifetime, which of these is most likely to help the organism respond
properly to changes in its environment?
A) microevolution
B) change in allele or gene frequency
C) change in gene expression
D) change in average heterozygosity
2) If, on average, 46% of the loci in a species’ gene pool are heterozygous, then the average
homozygosity of the species should be
A) 23%.
B) 46%.
C) 54%.
D) There is not enough information to say.
3) Which of these variables is likely to undergo the largest change in value as the result of a mutation
that introduces a brand-new allele into a population’s gene pool at a locus that had formerly been fixed?
A) average heterozygosity
B) nucleotide variability
C) geographic variability
D) average number of loci
4) Which statement about the beak size of finches on the island of Daphne Major during prolonged
drought is true?
A) Each bird evolved a deeper, stronger beak as the drought persisted.
B) Each bird’s survival was strongly influenced by the depth and strength of its beak as the drought
persisted.
C) Each bird that survived the drought produced only offspring with deeper, stronger beaks than seen in
the previous generation.
D) The frequency of the strong-beak alleles increased in each bird as the drought persisted.
5) Although each of the following has a better chance of influencing gene frequencies in small
populations than in large populations, which one most consistently requires a small population as a
precondition for its occurrence?
A) mutation
B) nonrandom mating
C) genetic drift
D) natural selection
E) gene flow
6) In modern terminology, diversity is understood to be a result of genetic variation. Which of the
following is a recognized source of variation for evolution?
A) mistakes in translation of structural genes
B) mistakes in protein folding
C) rampant changes to the dictionary of the genetic code
D) binary fission
E) recombination by crossing over in meiosis
7) A trend toward the decrease in the size of plants on the slopes of mountains as altitudes increase is an
example of
A) a cline.
B) a bottleneck.
C) relative fitness.
D) genetic drift.
E) geographic variation.
8) The higher the proportion of loci that are “fixed” in a population, the lower is that population’s
A) nucleotide variability only.
B) genetic polyploidy only.
C) average heterozygosity only.
D) nucleotide variability, average heterozygosity, and genetic polyploidy.
E) nucleotide variability and average heterozygosity only.
9) Which statement about variation is true?
A) All phenotypic variation is the result of genotypic variation.
B) All genetic variation produces phenotypic variation.
C) All nucleotide variability results in neutral variation.
D) All new alleles are the result of nucleotide variability.
E) All geographic variation results from the existence of clines.
10) Rank the following one-base point mutations (from most likely to least likely) with respect to their
likelihood of affecting the structure of the corresponding polypeptide:
1. insertion mutation deep within an intron
2. substitution mutation at the third position of an exonic codon
3. substitution mutation at the second position of an exonic codon
4. deletion mutation within the first exon of the gene
A) 1, 2, 3, 4
B) 4, 3, 2, 1
C) 2, 1, 4, 3
D) 3, 1, 4, 2
E) 2, 3, 1, 4
11) Most invertebrates have a cluster of ten similar Hox genes, all located on the same chromosome.
Most vertebrates have four such clusters of Hox genes, located on four nonhomologous chromosomes.
The process that could have potentially contributed to the cluster’s presence on more than one
chromosome was ________.
A) binary fission
B) translation
C) gene duplication
D) nondisjunction
E) transcription
12) Which of the following is a true statement concerning genetic variation?
A) It is created by the direct action of natural selection.
B) It arises in response to changes in the environment.
C) It must be present in a population before natural selection can act upon the population.
D) It tends to be reduced by the processes involved when diploid organisms produce gametes.
E) A population that has a higher average heterozygosity has less genetic variation than one with a lower
average heterozygosity.
13) How many of these statements regarding populations are true?
1. Mature males and females of a population can interbreed with each other.
2. Populations are sometimes geographically isolated from other populations.
3. Biological species are made up of populations.
4. Members of a population tend to be genetically more similar to each other than to members of other
populations.
5. Populations have genomes, but not gene pools.
A) Only one of these statements is true.
B) Two of these statements are true.
C) Three of these statements are true.
D) Four of these statements are true.
E) All five of these statements are true.
14) Whenever diploid populations are in Hardy-Weinberg equilibrium at a particular locus
A) the allele’s frequency should not change from one generation to the next, but its representation in
homozygous and heterozygous genotypes may change.
B) natural selection, gene flow, and genetic drift are acting equally to change an allele’s frequency.
C) this means that, at this locus, two alleles are present in equal proportions.
D) the population itself is not evolving, but individuals within the population may be evolving.
15) In the formula for determining a population’s genotype frequencies, the 2 in the term 2pq is
necessary because
A) the population is diploid.
B) heterozygotes can come about in two ways.
C) the population is doubling in number.
D) heterozygotes have two alleles.
16) In the formula for determining a population’s genotype frequencies, the pq in the term 2pq is
necessary because
A) the population is diploid.
B) heterozygotes can come about in two ways.
C) the population is doubling in number.
D) heterozygotes have two alleles.
17) Hardy-Weinberg equilibrium must occur in populations wherein
A) an allele remains fixed.
B) no genetic variation exists.
C) natural selection is not operating.
D) All three of the responses above are correct.
E) Only two of the responses above are correct.
18) In a Hardy-Weinberg population with two alleles, A and a, that are in equilibrium, the frequency of
the allele a is 0.3. What is the percentage of the population that is homozygous for this allele?
A) 0.09
B) 0.49
C) 0.9
D) 9.0
E) 49.0
19) In a Hardy-Weinberg population with two alleles, A and a, that are in equilibrium, the frequency of
allele a is 0.2. What is the percentage of the population that is heterozygous for this allele?
A) 0.2
B) 2.0
C) 4.0
D) 16.0
E) 32.0
20) In a Hardy-Weinberg population with two alleles, A and a, that are in equilibrium, the frequency of
allele a is 0.1. What is the frequency of individuals with AA genotype?
A) 0.20
B) 0.32
C) 0.42
D) 0.81
E) Genotype frequency cannot be determined from the information provided.
21) You sample a population of butterflies and find that 56% are heterozygous at a particular locus.
What should be the frequency of the recessive allele in this population?
A) 0.07
B) 0.08
C) 0.09
D) 0.70
E) Allele frequency cannot be determined from this information.
22) In peas, a gene controls flower color such that R = purple and r = white. In an isolated pea patch,
there are 36 purple-flowering plants and 64 white-flowering plants. Assuming Hardy-Weinberg
equilibrium, what is the value of q for this population?
A) 0.36
B) 0.64
C) 0.75
D) 0.80
23) Evolution
A) must happen, due to organisms’ innate desire to survive.
B) must happen whenever a population is not well-adapted to its environment.
C) can happen whenever any of the conditions for Hardy-Weinberg equilibrium are not met.
D) requires the operation of natural selection.
E) requires that populations become better suited to their environments.
24) Over time, the movement of people on Earth has steadily increased. This has altered the course of
human evolution by increasing
A) nonrandom mating.
B) geographic isolation.
C) genetic drift.
D) gene flow.
25) Swine are vulnerable to infection by bird flu virus and human flu virus, which can both be present in
an individual pig at the same time. When this occurs, it is possible for genes from bird flu virus and
human flu virus to be combined, thereby producing a genetically distinctive virus, which can
subsequently cause widespread disease.
The production of new types of flu virus in the manner described above is most similar to the
phenomenon of
A) bottleneck effect.
B) founder effect.
C) natural selection.
D) gene flow.
E) sexual selection.
26) If the original finches that had been blown over to the Galápagos from South America had already
been genetically different from the parental population of South American finches, even before adapting
to the Galápagos, this would have been an example of
A) genetic drift.
B) bottleneck effect.
C) founder effect.
D) all three of these.
E) both the first and third of these.
27) What is true of natural selection?
A) Natural selection is a random process.
B) Natural selection creates beneficial mutations.
C) The only way to eliminate harmful mutations is through natural selection.
D) Mutations occur at random; natural selection can preserve and distribute beneficial mutations.
E) Mutations occur when directed by the good of the species; natural selection edits out harmful
mutations and causes populations to adapt to the beneficial mutations.
28) The restriction enzymes of bacteria protect the bacteria from successful attack by bacteriophages,
whose genomes can be degraded by the restriction enzymes. The bacterial genomes are not vulnerable to
these restriction enzymes because bacterial DNA is methylated. This situation selects for bacteriophages
whose genomes are also methylated. As new strains of resistant bacteriophages become more prevalent,
this in turn selects for bacteria whose genomes are not methylated and whose restriction enzymes
instead degrade methylated DNA. The outcome of the conflict between bacteria and bacteriophage at
any point in time results from
A) frequency-dependent selection.
B) evolutionary imbalance.
C) heterozygote advantage.
D) neutral variation.
E) genetic variation being preserved by diploidy.
29) The restriction enzymes of bacteria protect the bacteria from successful attack by bacteriophages,
whose genomes can be degraded by the restriction enzymes. The bacterial genomes are not vulnerable to
these restriction enzymes because bacterial DNA is methylated. This situation selects for bacteriophages
whose genomes are also methylated. As new strains of resistant bacteriophages become more prevalent,
this in turn selects for bacteria whose genomes are not methylated and whose restriction enzymes
instead degrade methylated DNA. Over the course of evolutionary time, what should occur?
A) Methylated DNA should become fixed in the gene pools of bacterial species.
B) Nonmethylated DNA should become fixed in the gene pools of bacteriophages.
C) Methylated DNA should become fixed in the gene pools of bacteriophages.
D) Methylated and nonmethylated strains should be maintained among both bacteria and
bacteriophages, with ratios that vary over time.
E) Both the first and second responses are correct.
30) Arrange the following from most general (i.e., most inclusive) to most specific (i.e., least inclusive):
1 natural selection
2. microevolution
3. intrasexual selection
4. evolution
5. sexual selection
A) 4, 1, 2, 3, 5
B) 4, 2, 1, 3, 5
C) 4, 2, 1, 5, 3
D) 1, 4, 2, 5, 3
E) 1, 2, 4, 5, 3
31) Sexual dimorphism is most often a result of
A) pansexual selection.
B) stabilizing selection.
C) intrasexual selection.
D) intersexual selection.
E) artificial selection.
32) In the wild, male house finches (Carpodus mexicanus) vary considerably in the amount of red
pigmentation in their head and throat feathers, with colors ranging from pale yellow to bright red. These
colors come from carotenoid pigments that are found in the birds’ diets; no vertebrates are known to
synthesize carotenoid pigments. Thus, the brighter red the male’s feathers are, the more successful he has
been at acquiring the red carotenoid pigment by his food-gathering efforts (all other factors being equal).
During breeding season, one should expect female house finches to prefer to mate with males with the
brightest red feathers. Which of the following is true of this situation?
A) Alleles that promote more efficient acquisition of carotenoid-containing foods by males should
increase over the course of generations.
B) Alleles that promote more effective deposition of carotenoid pigments in the feathers of males should
increase over the course of generations.
C) There should be directional selection for bright red feathers in males.
D) Three of the statements are correct.
E) Two of the statements are correct.
33) During breeding season, one should expect female house finches to prefer to mate with males with
the brightest red feathers. Which of the following terms are appropriately applied to this situation?
A) sexual selection
B) mate choice
C) intersexual selection
D) Three of the responses are correct.
E) Two of the responses are correct.
34) Adult male humans generally have deeper voices than do adult female humans, which is the direct
result of higher levels of testosterone causing growth of the larynx. If the fossil records of apes and
humans alike show a trend toward decreasing larynx size in adult females and increasing larynx size in
adult males, then
A) sexual dimorphism was developing over time in these species.
B) intrasexual selection seems to have occurred.
C) stabilizing selection was occurring in these species concerning larynx size.
D) selection was acting more directly upon genotype than upon phenotype.
35) Adult male humans generally have deeper voices than do adult female humans, which is the direct
result of higher levels of testosterone causing growth of the larynx. If one excludes the involvement of
gender in the situation, then the pattern that is apparent in the fossil record is most similar to one that
should be expected from
A) pansexual selection.
B) directional selection.
C) disruptive selection.
D) stabilizing selection.
E) asexual selection.
36) Which of the following statements best summarizes evolution as it is viewed today?
A) It represents the result of selection for acquired characteristics.
B) It is synonymous with the process of gene flow.
C) It is the descent of humans from the present-day great apes.
D) It is the differential survival and reproduction of the most-fit phenotypes.
37) Which of the following is most likely to produce an African butterfly species in the wild whose
members have one of two strikingly different color patterns?
A) artificial selection
B) directional selection
C) stabilizing selection
D) disruptive selection
E) sexual selection
38) Most Swiss starlings produce four to five eggs in each clutch. Starlings producing fewer, or more,
than this have reduced fitness. Which of the following terms best describes this situation?
A) artificial selection
B) directional selection
C) stabilizing selection
D) disruptive selection
E) sexual selection
39) The recessive allele that causes phenylketonuria (PKU) is harmful, except when an infant’s diet lacks
the amino acid phenylalanine. What maintains the presence of this harmful allele in a population’s gene
pool?
A) heterozygote advantage
B) stabilizing selection
C) diploidy
D) balancing selection
40) Heterozygote advantage should be most closely linked to which of the following?
A) sexual selection
B) stabilizing selection
C) random selection
D) directional selection
E) disruptive selection
41) In seedcracker finches from Cameroon, small- and large-billed birds specialize in cracking soft and
hard seeds, respectively. If long-term climatic change resulted in all seeds becoming hard, what type of
selection would then operate on the finch population?
A) disruptive selection
B) directional selection
C) stabilizing selection
D) No selection would operate because the population is in Hardy-Weinberg equilibrium.
42) When imbalances occur in the sex ratio of sexual species that have two sexes (i.e., other than a 50:50
ratio), the members of the minority sex often receive a greater proportion of care and resources from
parents than do the offspring of the majority sex. This is most clearly an example of
A) sexual selection.
B) disruptive selection.
C) balancing selection.
D) stabilizing selection.
E) frequency-dependent selection.
43) The same gene that causes various coat patterns in wild and domesticated cats also causes the cross–
eyed condition in these cats, the cross-eyed condition being slightly maladaptive. In a hypothetical
environment, the coat pattern that is associated with crossed eyes is highly adaptive, with the result that
both the coat pattern and the cross-eyed condition increase in a feline population over time. Which
statement is supported by these observations?
A) Evolution is progressive and tends toward a more perfect population.
B) Phenotype is often the result of compromise.
C) Natural selection reduces the frequency of maladaptive genes in populations over the course of time.
D) Polygenic inheritance is generally maladaptive, and should become less common in future
generations.
E) In all environments, coat pattern is a more important survival factor than is eye-muscle tone.
44) A proficient engineer can easily design skeletal structures that are more functional than those
currently found in the forelimbs of such diverse mammals as horses, whales, and bats. The actual
forelimbs of these mammals do not seem to be optimally arranged because
A) natural selection has not had sufficient time to create the optimal design in each case, but will do so
given enough time.
B) in many cases, phenotype is not merely determined by genotype, but by the environment as well.
C) though we may not consider the fit between the current skeletal arrangements and their functions
excellent, we should not doubt that natural selection ultimately produces the best design.
D) natural selection is generally limited to modifying structures that were present in previous
generations and in previous species.
45) There are those who claim that the theory of evolution cannot be true because the apes, which are
supposed to be closely related to humans, do not likewise share the same large brains, capacity for
complicated speech, and tool-making capability. They reason that if these features are generally
beneficial, then the apes should have evolved them as well. Which of these provides the best argument
against this misconception?
A) Advantageous alleles do not arise on demand.
B) A population’s evolution is limited by historical constraints.
C) Adaptations are often compromises.
D) Evolution can be influenced by environmental change.
Art Questions
46) Blue light is that portion of the visible spectrum that penetrates the deepest into bodies of water.
Ultraviolet (UV) light, though, can penetrate even deeper. A gene within a population of marine fish that
inhabits depths from 500 m to 1,000 m has an allele for a photopigment that is sensitive to UV light, and
another allele for a photopigment that is sensitive to blue light. Which of the following graphs best
depicts the predicted distribution of these alleles within a population if the fish that carry these alleles
prefer to locate themselves where they can see best?
A) A
B) B
C) C
D) D