Chapter 16: Population Genetics and Evolution
Topic: population genetics and evolution Difficulty: easy
1. __________ and its biota were a source of inspiration to Charles Darwin as he formulated his
theory of evolution by natural selection. This place also remains a mecca for biologists like
Peter and Rosemary Grant who are interested in the study of evolutionary biology.
A) Antarctica
D) The Galapagos Islands
B) Australia
E) The California Channel Islands
C) The Orkney Islands
Answer: D
Topic: population genetics and evolution Difficulty: easy
2. Why did average bill size increase dramatically in surviving individuals of Darwin's medium
ground finch (and their progeny) during a severe drought affecting Daphne Major Island?
A) Individuals eating harder seeds developed larger bills and passed this trait on to their
offspring.
B) Individuals with larger bills could eat the harder seeds available and survived better than
individuals with smaller bills.
C) Individuals with larger bills are always at an advantage on Daphne Major.
Answer: B
Topic: molecular basis of evolution Difficulty: moderate
3. A given amino acid is encoded by only a single, unique base sequence in DNA.
A) true B) false
Answer: B
Topic: mutation Difficulty: easy
4. A new protein produced by a mutant gene may or may not have properties different from those
of the original protein. If its properties are altered, these properties are most likely to be
__________ to the individual.
A) beneficial B) harmful C) neutral
Answer: B
Topic: mutation Difficulty: easy
5. Mutation is a random force in evolution that produces genetic variation independently of the
fitness consequences of the genetic change for the individual that bears the mutation.
A) true B) false
Answer: A
Topic: mutation Difficulty: moderate
6. The probability that an individual complex organism (such as a vertebrate) is likely to sustain
one or more mutations in some part of its genome during its lifetime is:
A) zero. B) slight, but close to zero. C) small. D) high.
Answer: D
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Chapter 16: Population Genetics and Evolution
Topic: population genetics Difficulty: moderate
7. A2 and B2 are equally rare alleles of genes A and B, much less frequent in the gene pool of a
population than the common alleles A1 and B1. Compared to the probability of an individual
having either A2 or B2, what is the probability of an individual having both A2 and B2?
A) greater B) about the same C) lower
Answer: C
Topic: Hardy-Weinberg equilibrium Difficulty: easy
8. The Hardy-Weinberg law states that the frequencies of alleles and genotypes remain constant
from generation to generation in a population with __________.
A) a large number of individuals
B) random mating
C) no selection
D) no mutation
E) no migration between populations
F) All of the above conditions must be met.
Answer: F
Topic: Hardy-Weinberg equilibrium Difficulty: moderate
9. In a particular population, gene A has only two alleles, A1 and A2. The frequencies of these two
alleles are known and designated p and q, respectively. What would the equilibrium frequency
of the genotype A1A2 be?
A) p2 B) q2 C) pq D) 2pq E) p2 + 2pq + q2
Answer: D
Topic: Hardy-Weinberg equilibrium Difficulty: easy
10. In a particular population, gene A has only two alleles, A1 and A2. The frequencies of these two
alleles are known and you calculate the Hardy-Weinberg equilibrium frequencies of the three
possible genotypes, A1A1, A1A2, and A2A2. The actual frequencies of these genotypes in the
population depart substantially from the equilibrium frequencies. Which of the following
processes is responsible for this departure from equilibrium frequencies?
A) genetic drift
D) natural selection
B) assortative mating
E) any of the above, or some combination
C) migration
Answer: E
Topic: genetic drift Difficulty: easy
11. Genetic drift results from stochastic variation in birth and death rates, and it is thus most
important in __________ populations.
A) small B) medium C) large D) all
Answer: A
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Topic: genetic drift Difficulty: hard
12. A small population of a sexually reproducing lizards has dwindled to two individuals, one male
and one female. Both are heterozygous (B1B2) for the gene B. These individuals mate and
produce three offspring. The adults are then eaten by a bird. What is the probability that allele
B2 has become fixed in the population, which now consists of the three offspring?
A) 1/64 B) 1/32 C) 1/16 D) 1/27 E) 1/9 F) 1/3
Answer: A
Topic: founder events Difficulty: easy
13. A large "raft" of floating vegetation breaks loose from a tropical mainland area during a violent
hurricane. After days adrift, the raft reaches a small island. Among the animals on this raft are
eight lizards belonging to a species not previously found on the island. Several years later, the
population established by these individuals is studied carefully and found to have a __________
level of genetic variation than the parent (mainland) population from which the original eight
colonists came.
A) substantially enhanced B) similar C) substantially reduced
Answer: C
Topic: population bottleneck Difficulty: easy
14. A large "raft" of floating vegetation breaks loose from a tropical mainland area during a violent
hurricane. After days adrift, the raft reaches a small island. Among the animals on this raft are
eight lizards belonging to a species not previously found on the island. The population
established by these individuals remains small for many generations, resulting in genetic drift.
Study of this population reveals that its genetic diversity is extremely low. The situation leading
to this reduced genetic variability is referred to as a __________.
A) population meltdown
D) population bottleneck
B) population crash
E) population enhancement
C) population extinction
Answer: D
Topic: population bottleneck Difficulty: moderate
15. Which of the following species of East African carnivores has been monitored closely by
conservationists after the discovery that this animal has practically no genetic variation?
A) lion B) tiger C) bear D) cheetah E) leopard
Answer: D
Topic: assortative mating Difficulty: easy
16. Which of the following results in inbreeding?
A) negative assortative mating
C) random mating
B) positive assortative mating
D) abstinence
Answer: B
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Chapter 16: Population Genetics and Evolution
Topic: assortative mating Difficulty: moderate
17. Inbreeding is deleterious because it creates genetic problems and thus cannot confer benefits in
any situation.
A) true B) false
Answer: B
Topic: assortative mating Difficulty: moderate
18. Outbreeding is always desirable, even if matings occur between individuals separated by great
distances.
A) true B) false
Answer: B
Topic: assortative mating Difficulty: easy
19. In experiments with Banksia, researchers in Australia showed that individual plants:
A) can make distinctions among developing embryos on the basis of their genotypes.
B) cannot make distinctions among developing embryos on the basis of their genotypes.
Answer: A
Topic: deviations from Hardy-Weinberg... Difficulty: hard
20. A deficiency of heterozygotes in a population strongly indicates either positive assortative
mating or a Wahlund effect caused by population mixing. Another, less likely, possibility is that
the population is undergoing __________.
A) stabilizing section
C) disruptive selection
B) directional selection
D) frequency-dependent selection
Answer: C
Topic: geographic variation Difficulty: easy
21. Plants of yarrow, Achillea millefolium, grown from seed collected from various habitats ranging
from sea level to more than 3,000 meters in elevation, retained distinctive differences in plant
size and other traits when grown in a common garden at sea level, indicating the existence of
__________ variation.
A) random B) catastrophic C) ecotypic D) assortative
Answer: C
Topic: geographic variation Difficulty: moderate
22. Frequencies of alleles in different populations of the snail Bradybaena in Japan bear no
relationship to habitat or locality. The observed pattern of genotypic variation has been
explained by the repeated introduction of this snail over the past 200 years. Each introduction
involved a small number of colonists containing a random, but not necessarily representative,
sample of the genetic variation present in the parent population. In other words, genetic
variation in Japanese Bradybaena reflects multiple __________.
A) founder events B) extinction events C) mutation events D) clinal events
Answer: A
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Chapter 16: Population Genetics and Evolution
Topic: geographic variation Difficulty: easy
23. Rivers can vary in their effectiveness as barriers to dispersal, as evidenced by studies of the
saddleback tamarin (Sanguinus fuscicollis) in the western Amazon Basin of Brazil. The Rio
Juruá is an effective barrier to dispersal except at its __________, where certain genotypes are
less clearly restricted to one side of the river or the other.
A) mouth B) middle portion C) headwaters
Answer: C
Topic: natural selection Difficulty: moderate
24. Weight at birth of human babies has a genetic component. In one large study, survival in a
cohort of babies during the first month of life was shown to be greatest for babies of average
weight at birth and least for babies with very low or very high weights at birth. Survivors of the
first month of life had lower variation in weight at birth than did all babies in the cohort.
Differential survival of this kind could result in __________ on genes controlling weight at birth.
A) stabilizing selection
C) disruptive selection
B) directional selection
D) no selection
Answer: A
Topic: natural selection Difficulty: moderate
25. Runaway sexual selection, in which female mating preference favors males with extreme
phenotypes, is a case of __________.
A) stabilizing selection
C) disruptive selection
B) directional selection
D) frequency-dependent selection
Answer: B
Topic: directional selection Difficulty: moderate
26. The rate of change in the frequency of a deleterious allele experiencing selective pressure varies
in direct relationship to:
A) the length in base pairs of the allele.
D) A and B.
B) the strength of the selective pressure.
E) B and C.
C) the frequency of the allele.
Answer: E
Topic: maintenance of genetic variation Difficulty: moderate
27. Which of the following can maintain or even enhance the level of genetic variation present in a
population?
A) mutation
B) migration
C) spatial/temporal environmental variation
D) heterozygote superiority
E) frequency-dependent selection
F) all of the above
Answer: F
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Chapter 16: Population Genetics and Evolution
Topic: heterozygote superiority Difficulty: easy
28. Heterozygote superiority in the case of the sickle-cell trait is dependent on environmental
conditions, in particular:
A) the presence of virulent poliomyelitis.
B) the presence of virulent schistosomiasis.
C) the presence of virulent malaria.
D) the presence of human immunodeficiency virus.
E) none of the above.
Answer: C
Topic: directional selection Difficulty: moderate
29. In his studies of the peppered moth, Biston betularia, B.D. Kettlewell demonstrated that the
ultimate selective agent leading to changes in genotypic frequencies was:
A) predation by birds.
B) poisoning of moths caused by industrial pollution.
C) indiscriminant use of pesticides.
D) all of the above.
Answer: A
Topic: directional selection Difficulty: moderate
30. An interesting and gratifying footnote to the long-term study of the peppered moth, Biston
betularia, in England has been the recent:
A) increase in the melanistic form.
B) stabilization of the melanistic form.
C) decline of the melanistic form.
D) demonstration that coloration in peppered moths has no selective value.
Answer: C
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Chapter 16: Population Genetics and Evolution
Use the following to answer questions 31-37:
You're the steward for your local land trust, the Tri-City Land Conservancy (also known as TLC). Land
trusts acquire and manage land for various purposes including conservation, which is the principal goal
of TLC. Among its other acquisitions, TLC has purchased various small tracts of land harboring
populations of a rare plant, the tri-city trumpet. Trumpets occur only on rock outcrops with shallow
soils. One of your principal assignments as the TLC steward is to study and manage populations of the
trumpet. The plant is well known for its showy, trumpet-like flowers. Its fleshy fruits are eaten by
birds, which disperse seeds. The plant has perfect flowers, but it is an obligate outcrosser, pollinated by
butterflies and hummingbirds. Plants have red, white, or pink flowers, and flower color is controlled by
a single gene. There are two alleles of this gene, R and r. Plants homozygous for R produce red
flowers, plants homozygous for r have white flowers, and heterozygous plants have pink flowers. Most
populations apparently contain both alleles, because red, pink, and white flowers are commonly seen.
Topic: founder events Difficulty: moderate
31. Among the tracts of rocky land you're managing is one that lacked trumpets until recently. The
tract is isolated from others supporting subpopulations of the trumpet, but TLC was anxious to
acquire this land because of its potential to support a trumpet subpopulation. Last summer you
indeed discovered a small trumpet subpopulation on this tract (three plants), probably established
from seed transported by birds. All the plants flowered and all had white flowers. Because most
subpopulations of this species have plants with all three colors, why does this one produce only
white flowers?
Answer: This appears to be an example of a founder event. Because all individuals in this
subpopulation produce white flowers, the subpopulation clearly contains only the r allele, and all
individuals have the homozygous genotype rr. One likely scenario is that a bird fed on trumpet
fruits in a nearby subpopulation and deposited a few seeds at this site. By chance, all the seeds
producing plants were of the white genotype. Any further reproduction within this
subpopulation will also result in plants with white flowers.
Topic: Hardy-Weinberg equilibrium Difficulty: hard
32. There is a fairly large subpopulation of trumpets on a rock outcrop near the one where you've
just discovered the new subpopulation of white-flowered plants (question 31). The large
subpopulation was recently inventoried and found to have 36% red-flowered plants, 48% pinkflowered plants, and 16% white-flowered plants. What are the frequencies of the R and r alleles
in this large subpopulation and is the subpopulation in Hardy-Weinberg equilibrium?
Answer: One way to solve this problem is to consider the alleles present in a representative
collection of 100 plants. There would be 200 alleles among these 100 plants. The 36 redflowered plants would have 72 R alleles; the 48 pink-flowered plants would have 48 R alleles
and 48 r alleles; and the 16 white-flowered plants would have 32 r alleles. Thus the frequency of
R alleles would be 120/200 = 0.6 and the frequency of r alleles would be 80/200 = 0.4. The
population can be shown to be in Hardy-Weinberg equilibrium. If the frequencies of the R and r
alleles are labeled p and q, respectively, then proportions of red-flowered plants should be p2 =
0.36, pink-flowered plants 2pq = 0.48, and white-flowered plants q2 = 0.16, respectively. These
are the observed proportions in this large subpopulation.
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Chapter 16: Population Genetics and Evolution
Topic: founder events Difficulty: moderate
33. Because the large subpopulation (question 32) of trumpets is the only one located near the new
white-flowered subpopulation (question 31), you suspect that seed from the large subpopulation
probably established the new subpopulation. Given what you know about the large
subpopulation, what is the probability that three seeds taken at random from this subpopulation
would have the white genotype?
Answer: The white genotype occurs with a frequency 0.16 in the large subpopulation. The
probability of drawing three seeds at random from this subpopulation and having all three be
homozygous for the r allele is 0.16  0.16  0.16 = 0.004096 or about 1 in 244. While this is an
unlikely scenario, it is certainly not out of the question!
Topic: Hardy-Weinberg equilibrium Difficulty: hard
34. Although most of the trumpet subpopulations on TLC holdings contain both the R and r alleles in
some mixture, there are two subpopulations of moderate size that are each fixed for one of the
two alleles. Thus one subpopulation currently has only red-flowered plants and the other has
only white-flowered plants. Between them is a rocky area owned by TLC that lost its trumpet
population several years ago because of illegal collecting. You decide to reestablish this
subpopulation, and you do so by transplanting 50 red-flowered plants from one of the adjacent
subpopulations and 50 white-flowered plants from the other, thus ensuring genetic diversity.
Although this new subpopulation now has a 50:50 mix of the R and r alleles, it is not in HardyWeinberg equilibrium. How do you know this?
Answer: If this subpopulation were in Hardy-Weinberg equilibrium, it would have 25% red-,
50% pink-, and 25% white-flowered individuals, reflecting the 0.5 allelic frequencies of R and r.
Topic: Wahlund effect Difficulty: hard
35. In the artificially established subpopulation described in the previous question, you have
inadvertently created an example of a well-known departure from Hardy-Weinberg equilibrium.
What is this effect called? Describe this effect.
Answer: You have created an extreme example of the Wahlund effect, in which a mixture of two
subpopulations has a deficiency of heterozygotes. Your newly established subpopulation has no
heterozygotes, although it should have 50% heterozygotes under Hardy-Weinberg equilibrium.
Topic: inbreeding depression Difficulty: moderate
36. Over the years, you've had experience with several very small, isolated subpopulations of
trumpets. Typically, such populations have declined in size, despite having excellent growing
conditions. The plants have performed poorly and seed set has often been far less than that
experienced by larger populations. What is your assessment of the probable cause of this poor
performance?
Answer: A probable cause of the poor performance in these small, isolated populations is
inbreeding depression. Continued interbreeding among closely related individuals can result in
loss of heterozygosity and expression of deleterious recessive alleles, leading to an overall loss
of vigor in the subpopulation.
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Chapter 16: Population Genetics and Evolution
Topic: optimal outcrossing distance Difficulty: moderate
37. Curious about the potential for inbreeding depression in trumpets, you establish an experiment in
which flowers of trumpets are fertilized with pollen from nearby plants (within 1 m), plants at
intermediate distance (100 m), and plants at extreme distance (10,000 m). You discover that the
best performance (measured as seed set and subsequent survival of offspring) results from
crosses at intermediate distance. Why?
Answer: Your study helps identify an optimal outcrossing distance. Crosses with nearby plants,
likely to be close relatives, result in inbreeding depression. Crosses with plants from
intermediate distances eliminate inbreeding depression, whereas crosses with distant plants result
in outbreeding depression because distant plants have genetic adaptations to different conditions.
Topic: molecular basis of evolution Difficulty: easy
38. Molecules of DNA are comprised of 4 kinds of subunits (adenine, thymine, cytosine, and
guanine) called __________.
Answer: nucleotides
Topic: molecular basis of evolution Difficulty: easy
39. Each amino acid in a protein is encoded by a sequence of three subunits of a DNA molecule;
such a coding sequence is referred to as a __________.
Answer: codon
Topic: molecular basis of evolution Difficulty: easy
40. Certain mutations are referred to as __________ because the mutated coding sequence still codes
for the same amino acid as the unmutated coding sequence. Such mutations have no
consequences for fitness.
Answer: silent
Topic: recombination Difficulty: moderate
41. __________ is the exchange of homologous sections of maternal and paternal chromosomes
during the formation of gametes.
Answer: Recombination
Topic: assortative mating Difficulty: moderate
42. __________ is the reduction of fitness caused by inbreeding.
Answer: Inbreeding depression
Topic: geographic variation Difficulty: moderate
43. Sometimes allele frequencies, or phenotypic characters under genetic influence, vary gradually
within a species along a geographic transect spanning a substantial distance. Such gradual
geographic variation is referred to as a __________.
Answer: cline
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Chapter 16: Population Genetics and Evolution
Topic: geographic variation Difficulty: moderate
44. We recognize the Swedish botanist __________ for his pioneering work with common garden
experiments that identified ecotypes, genetically differentiated populations restricted to specific
habitats.
Answer: Turreson
Topic: directional selection Difficulty: easy
45. Increased frequency of dark-colored forms of the moth Biston betularia in England was
associated with industrial development leading to darkening of tree trunks. Because of this, the
increased frequency of dark moths has been dubbed __________.
Answer: industrial melanism
Topic: Hardy-Weinberg equilibrium Difficulty: hard
46. A population will remain in Hardy-Weinberg equilibrium only when a number of fairly
restrictive conditions are met. Why do population geneticists place so much emphasis on an
equilibrium condition from which populations so frequently deviate?
Answer: The Hardy-Weinberg equilibrium provides a "benchmark" against which genotypic
frequencies may be compared. Deviations from the frequencies expected under Hardy-Weinberg
equilibrium is evidence of the action of one or more of the following processes: natural selection,
nonrandom mating, gene flow related to migration, genetic drift, or significant mutation rate.
The knowledge that one or more of these processes may be operating in a population is
important, because it indicates that a search for the cause of nonequilibrium genotypic
frequencies will be worthwhile.
Topic: mutation Difficulty: hard
47. Mutation is a weak force with respect to changes in allelic frequencies and the generation of
novel genotypic combinations, and yet population geneticists view mutation as the foundation
upon which all changes in genetic makeup of populations is based. Please discuss this apparent
contradiction.
Answer: Mutation is a weak force compared, say, to natural selection, in causing deviations from
Hardy-Weinberg equilibrium. Under appropriate conditions, selection and other processes, such
as nonrandom mating, gene flow related to migration, and genetic drift, can lead to substantial
departures from equilibrium genotypic frequencies. While not contributing to shifts in
equilibrium genotypic frequencies, recombination produces new genotypic combinations at a
rate far greater than that caused by mutation. However, mutation is the ultimate cause of genetic
variation in a population, providing the raw material upon which other processes operate.
Without the novel alleles continually produced by mutation, processes such as natural selection
would lack the genetic variation upon which their action depends.
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Chapter 16: Population Genetics and Evolution
Topic: assortative mating Difficulty: moderate
48. What is assortative mating, and what are its consequences?
Answer: Assortative mating occurs when individuals choose their mates in a nonrandom fashion
with respect to their own genotypes. Mating biased toward individuals with similar genetic
makeup is referred to as positive assortative mating. Mating biased toward individuals with
different genetic makeup is called negative assortative mating. Whereas assortative mating
cannot directly affect frequencies of different alleles in a population, it can result in departures of
genotypic frequencies from Hardy-Weinberg equilibrium. For example, positive assortative
mating, also called inbreeding, can increase the proportion of homozygotes while reducing the
proportion of heterozygotes in the population. Greater expression of deleterious recessive alleles
can lead to changes in allelic frequencies when natural selection operates against less fit allelic
combinations expressed in greater frequency with inbreeding.
Topic: genetic variation Difficulty: hard
49. Directional selection acts to remove genetic variation from populations. Given that directional
selection is a potent force leading to evolutionary change, why doesn't the genetic variation in a
population gradually dwindle away until only a single, highly fit genotype remains?
Answer: There are many other forces that act to maintain genetic diversity in populations.
Mutations continue to occur, introducing new alleles or reintroducing old ones that have been
eliminated. In certain situations, the fitness of heterozygotes may be superior to that of
homozygotes, resulting in retention of allelic diversity. Another process maintaining genetic
diversity is frequency-dependent selection, in which the relative fitness of genotypes
incorporating rare alleles is enhanced. Finally, it is important to keep in mind that both biotic
and abiotic environments are subject to continual change. The relative fitnesses of various
genotypes are constantly changing as the environmental background against which they are
tested also changes.
Topic: ecological lessons of population genetic Difficulty: moderate
50. What useful lessons can ecologists learn from studies of population genetics?
Answer: Ecologists can draw many useful lessons from studies of population genetics. First,
most natural populations contain substantial genetic variation maintained and enhanced by a
number of important processes. It is this store of genetic variation, and the continual generation
of new genetic variation, that provides resiliency for populations faced with continually changing
environmental challenges. Second, changes in selective pressures in the environment will be met
with evolutionary responses leading to shifts in genotypic frequencies within populations. In
other words, evolution is an ongoing process. Third, human intervention can overwhelm the
capability of natural systems to respond to environmental challenges. By fostering situations in
which genetic diversity is depleted (as is the case in small, fragmented populations), humans
reduce the inherent resiliency of populations. By causing extremely rapid changes in the
physical environment or by rapidly altering the biotic makeup of natural communities (through
introductions, extinctions, etc.), humans create situations that can overwhelm the capacity of
populations to respond through evolutionary change, leading to further extinctions and, in the
worst case, collapse of entire ecosystems.
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