Chapter 18
Student: _________________________________________________________
1. Which of the following would change the gene frequencies of a population?
A. DNA is stable from generation to generation and does not change.
B. Tall people in a population marry other tall people and do not marry people who are short or average height.
C. A population on an island remains isolated and no one leaves or moves onto the island.
D. None of the choices would change the gene frequencies of a population.
2. Which of the following would be a cause of microevolution?
A. A flood kills almost all the wild strawberry plants in a particular area.
B. The largest and strongest male lion chases away other males and is the only male to mate with females and
produce offspring.
C. Wolves are moved from Canada and introduced into the wild in Wyoming.
D. All of the choices can lead to microevolution
3. A certain species of butterfly in colors ranging from white to dark blue is found. The birds found in the same
area feed on the white or lightly colored butterflies, leaving butterflies that are darkly colored. This is an
example of:
A. stabilizing selection
B. disruptive selection
C. directional selection
4. All the members of a single species that occupy a particular area at the same time are known as a
A. subspecies.
B. gene pool.
C. population.
D. group.
E. sub-population.
5. Which of the following is/are a biological "population?"
A. all of the corn plants in a cornfield
B. all of the variable-colored ladybird beetles of the species Harmonia axyridis in a forest
C. all male and female English sparrows that reside in your community
D. all of the human population of a rural western town
E. All of the choices are correct.
6. What is the term used to describe the accumulation of small changes in the gene pool of a species over time?
A. genetic drift
B. founder effect
C. microevolution
D. directional selection
7. Which of these conditions is NOT among the requirements of the Hardy-Weinberg equilibrium?
A. no net mutations
B. no net migration of alleles into or out of the population
C. small population with genetic drift
D. no selection of one genotype over another
E. sexually reproducing and random mating population
8. If the Hardy-Weinberg equilibrium is met, what is the net effect?
A. evolution leading to a population better adapted to an unchanging environment
B. evolution leading to a population better adapted to a changing environment
C. very slow and continuous evolution with no increased adaptation
D. no evolution because the alleles in the population remain the same
9. A student proposes that left-handedness is a recessive trait that is therefore hidden in much of the human
population. A survey of a class of 36 students finds that 27 (0.75) are right-handed and 9 (0.25) are left-handed.
Using the Hardy-Weinberg formula, what would the expected genotype and allele frequencies be in this
theoretical population?
A. 0.75 right-handed homozygous dominant and 0.25 recessive homozygous for 3-to-1 right-to-left handed
alleles in the population
B. 0.25 right-handed homozygous, 0.50 heterozygous, and 0.25 recessive homozygous for a 3-to-1 right-to-left
handed alleles in the population
C. 0.25 right-handed homozygous, 0.50 heterozygous, and 0.25 recessive homozygous for a 0.5 allele frequency
for each allele
D. 0.50 right-handed homozygous, 0.25 heterozygous, and 0.25 recessive homozygous for a 0.5 allele
frequency for each allele
E. They cannot be estimated using these limited data.
10. Another student proposes that handedness could just as easily be passed to children by how the parents carry
the child and interact with it, a learning process that may perpetuate the parents' handedness. Assuming all
parents and children are expressing their "true handedness," the occurrence of which case below would cast the
most serious doubt on a simple genetic basis for handedness, with left-handedness recessive?
A. Two right-handed parents have a left-handed child.
B. Two left-handed parents have a right-handed child.
C. Left-handed parents only have left-handed children.
D. Right-handed parents only have right-handed children.
E. None of the choices is correct.
11. A random alteration in the sequence of DNA nucleotides that provides a new variant allele is
A. gene mutation.
B. polymorphism.
C. gene frequency.
D. disruption.
12. Which of the following reflect(s) the likely presence of (a) gene mutation(s)?
A. Fruit flies subjected to intense radiation breed a wider array of variable offspring.
B. A chemical leaking from the surface of an old abandoned coal mine alters a regulatory gene so that a cricket
nymph develops an extra set of eyes.
C. The bacteria that cause gonorrhea, a common sexually transmitted disease, have previously been killed by
penicillin; however, after continuous usage of the antibiotic, penicillin-resistant strains are now becoming
D. Radiation causes an alteration in a DNA nucleotide sequence, which is discovered when mapped, but which
appears to be neither increasing nor decreasing in successive generations.
E. All of the choices are correct.
13. Drug-resistance mutations occur in bacteria
A. only when they are exposed to the drug to which they become resistant.
B. more often when they are exposed to the drug.
C. at any time, even when they are not exposed to the drug.
D. only when they are exposed to radiation or other mutagens.
14. A mutation to a _______ form is more likely to be recognized than any other because ______.
A. beneficial, individuals with a beneficial mutation are much better adapted and survive longer in their
B. beneficial, individuals with a beneficial mutation will always be healthier and have more offspring than
C. neutral, these mutations make up the majority of changes in the species
D. harmful, these allow the individual to survive better in a different environment
E. harmful, species are already well adapted and few beneficial changes are possible—but many damaging
changes are possible and cause death or poor adaptation by the individual
15. The most common source of genetic variation in sexually reproducing organisms is
A. mutation.
B. recombination of alleles.
C. duplication of chromosomes.
D. duplication of genes.
16. Which of the following conditions contributes to evolution?
A. mutations
B. gene flow
C. genetic drift
D. natural selection
E. All of the choices are correct.
17. If the mutation rate of individual genes is taken to be about one in 100,000 genes per cell cycle across many
organisms, we might expect evolution to proceed at an even rate for various forms of life. Which factor could
make the accumulation of gene mutations faster or slower among different organisms?
A. Organisms with more genes will likely have more mutations per generation.
B. More selection of mutations can occur in a shorter period of time for bacteria that replicate each ten minutes
than for humans with a (roughly) 20-year generation span.
C. Organisms vary in the proportion of DNA that is active and in the percent of loci that have multiple alleles.
D. All of the choices are correct.
18. Our domesticated honey bee—originally from Europe—is slow to sting, requires abundant flower nectar,
gets up late in the morning, and stores much honey but only produces enough new brood to swarm once a year.
Because the European honey bee was performing poorly as a honey producer in South America, the African
subspecies was imported in a breeding experiment. The African honey bee formed small nests, foraged earlier
and on smaller nectar sources, produced less honey stores and more brood, swarmed four or five times a year,
and was fast to sting. However, when the African queens escaped, the two populations interbred and the African
genotype spread several hundred miles north each year. Surprisingly, a hundred miles behind the expanding
range of the African honey bees, the European and hybrid strains died out and the bees were essentially 100
percent African. How would this be explained in evolutionary genetics terms?
A. Gene flow is not occurring and therefore these are two separate species.
B. This is a natural consequence of the Hardy-Weinberg equilibrium.
C. Obviously the African bee genes are dominant over the European honey bee alleles.
D. Gene flow is occurring between these subspecies but the African bee is "ecologically better."
E. This can be understood as a classic case of genetic drift.
19. Occasionally, "living fossils" such as the coelacanth are found; these organisms appear to be little changed
from their ancestors preserved in rock strata many millions of years ago. Such organisms often occur in ocean
deeps and in soil and desert environments that change less often over time. This is an indication that
A. although gene mutations may be common, there may be little selection among individuals already well
adapted to a uniform environment.
B. these organisms do not have the same high mutation rate of most organisms.
C. by chance, these organism's mutations are all in alleles that do not affect morphology.
D. the Hardy-Weinberg equilibrium prevents these organisms from evolving very fast.
E. there is extensive inbreeding in such organisms.
20. Social research indicates that a person is most likely to marry someone from the same village or city, or a
high school or college classmate. Therefore, the Hardy-Weinberg equilibrium does not apply well to human
populations because
A. allelic changes in one direction are balanced by changes in the opposite direction.
B. there is no directional trend in selection of mates since most individuals marry someone.
C. individuals are not pairing up by chance across the whole population, and genetic drift is more likely to
change gene frequencies.
D. this increases gene flow.
E. we accumulate adaptive traits that improve the population.
21. Which statement is NOT true about nonrandom mating?
A. Inbreeding is mating between relatives more often than by chance.
B. Inbreeding is a change in allele frequencies that increases the proportion of heterozygotes in the population.
C. An example of assortative mating is when a tall man marries a tall woman.
D. Assortative mating tends to cause subdivision into two phenotypic classes with reduced gene flow between
22. If two adjacent populations of the same species show gene flow, then the two populations will
A. become more similar in their gene pools.
B. become isolated from each other.
C. develop into different species.
D. adapt to different conditions and become separate.
23. Which of the following is true about genetic drift?
A. It is more likely to occur in a large population than in a small population.
B. It may lead to an allele's becoming fixed in a population when its alternative allele is lost from the
C. It increases the number of heterozygotes in a population.
D. It increases the level of rare alleles in a population.
24. Which statement is NOT true about the founder effect?
A. It is a form of genetic drift.
B. It produces a high frequency of some rare alleles in a small isolated population.
C. Founding members contain a tiny fraction of the alleles found in the original population.
D. The founder effect occurs when a population is subjected to near extinction and then recovers so that only a
few alleles are left in survivors.
25. If early Viking explorers in Greenland and North America had survived and become the main ancestors of
early North American settlers, rather than the mixture of immigrants from across Europe and other continents,
today there would be a much higher incidence of Nordic traits in the U.S. population. Such a scenario would
A. gene flow from continent to continent.
B. the founder effect.
C. genetic drift among the original Viking explorers.
D. directional selection.
E. fitness for the North American environment.
26. In the case of the peppered moths in England, when Kettlewell set up cameras to document that more white
or black moths were eaten by birds on clean or sooty trees, he was verifying which factor involved in evolution
by natural selection?
A. The organisms vary in traits.
B. The variation is inherited.
C. More young are born than can survive.
D. Some individuals are better adapted to the environment.
27. Disruptive selection is described in the text with the case of British land snails. In the grassy fields, the
light-banded snails escape bird predators. In the darker forest, the dark snails survive and the light-banded snails
are eaten. As long as the snails continue to cruise across the British landscape mating at the same season, why
doesn't this "disruptive selection" eventually lead to two separate species?
A. There is no reproductive isolation to prevent gene flow.
B. They are already two separate species, and the intermediate forms are hybrids.
C. The color forms are probably not genetically determined.
D. There must be some unknown factor producing an equal stabilizing selection "to hold the species together."
E. This will result in the formation of two species if given long enough time.
28. Which of the following is required for natural selection to occur in a population?
A. variation in the population
B. inheritance of variation through genetic differences
C. differential reproduction so that more fit individuals have more offspring
D. accumulation of adaptive traits so that they increase in the population
E. All of the choices are required.
29. Which statement is NOT true about natural selection?
A. Directional selection occurs when one extreme phenotype is favored over another different extreme
B. Stabilizing selection favors an intermediate phenotype over either of the extreme phenotypes.
C. Disruptive selection favors both of the extreme phenotypes over the intermediate phenotype.
D. Directional selection leads to improved selection when the environment remains the same.
E. Disruptive selection leads to polymorphism, favoring different forms of the same species.
30. Which statement is NOT true about the maintenance of variation in a population?
A. Selection for adaptation to a particular environment ensures that the population will become stronger and
more viable under any conditions.
B. Only phenotypes are acted on by selection, so heterozygotes serve as a reservoir of recessive alleles that may
be adaptive in a different environment.
C. Heterozygote superiority may lead to selection for the heterozygote above either homozygote.
D. Variation is maintained through mutation, recombination, gene flow, and changed conditions.
31. The Latin term for "kind" is the root word for
A. mutation.
B. gene.
C. species.
D. child or kinder.
E. zygote.
32. Descriptions of new species of insects are more likely to contain diagrams of the shape of the male genitalia
than head, wing, or leg parts. Why?
A. This is where mutations usually express themselves in animals.
B. Radiation damage to genes usually occurs in genitalia.
C. Small changes in the genitalia cause reproductive isolation while a single species can tolerate wider variation
in head, wing, and leg morphology.
D. Arthropods have hard exoskeletons so head, wing, and leg structures can't vary as much.
E. This is the convention or custom of entomology.
33. Which of the following would result in reproductive isolation?
A. Two populations of crickets are indistinguishable in physical features, but the females in each group only
come to the different songs of their males.
B. Fruit flies on one Hawaiian island live for hundreds of generations and do not come in contact with fruit flies
on another island except when blown there by rare tropical storms.
C. One brood of the seventeen-year cicada emerged in 1987 (and will do so every 17 years) and lives a few
months as adults; another brood emerged in 1992 (and will do so every 17 years); the larvae of both feed sideby-side on tree roots.
D. A lion and a tiger mate in the artificial confines of a zoo but the offspring is infertile.
E. All of the choices are correct.
34. An insect population lives along the edge of a north-south mountain range. The populations from the east
and west slope eventually join in a low northern pass and interbreed, producing fertile offspring, but they do not
circle around the southern edge because of a desert barrier. When glaciers move southward, the populations are
pushed south of the northern pass and are isolated. While isolated, the two populations develop enough
differences over time that when the glaciers retreat north and the insects again share the same pass, they no
longer mate at the same time, nor can they produce fertile offspring. These insects
A. began as one species and therefore remain one species.
B. were originally two species and remain two species.
C. were originally two species but are now one species.
D. were originally one species but are now two species.
E. The number of species cannot be determined from the information given.
35. An insect population lives along the edge of a north-south mountain range. The populations from the east
and west slope eventually join in a low northern pass and interbreed, producing fertile offspring, but they do not
circle around the southern edge because of a desert barrier. When glaciers move southward, the populations are
pushed south of the northern pass and are isolated. While isolated, the two populations develop enough
differences over time that when the glaciers retreat north and the insects again share the same pass, they no
longer mate at the same time, nor can they produce fertile offspring. Insect populations on the mountain slopes
A. always allopatric.
B. always sympatric.
C. first allopatric, then sympatric, then allopatric.
D. first sympatric, then allopatric, then sympatric.
E. There is not enough information to determine sympatry or allopatry.
36. In the case of Darwin's finches, an ancestral finch species from the mainland arrived on the Galápagos
Islands and soon developed into many new species via adaptive radiation. The finches did NOT undergo
adaptive radiation back on the mainland. What is the most plausible biological explanation?
A. Directional selection works better on islands.
B. Competition from many other birds species on the mainland provided stabilizing selection that was absent on
the islands.
C. The environment on the mainland was completely uniform.
D. The founder effect greatly expanded the variation in alleles in the Galápagos finch gene pool.
E. The ancestral mainland finch was reproductively isolated.
37. While we have seen how natural selection and the use of pesticides can lead to the development of resistant
varieties of insects, two economically important flies, the Mediterranean fruit fly (Medfly) and the screwworm
fly, can be driven to local extinction by the continuous release of sterile flies of those species. The critical factor
is that the female of these species only mates once. But which of the following is/are also necessary for sterile
release to work?
A. The target species is truly just one species.
B. The insect can be raised artificially in large numbers.
C. The insects to be released can be sterilized with radiation without affecting their ability to attract a mate in
the wild.
D. All of the choices are correct.
38. Throughout the chapter, a wide range of evidence has been brought together to describe what constitutes a
species. From all of this you can conclude that
A. some day we could theoretically finalize a list of all species on earth and, if correct, it could remain
B. once mating experiments have been conducted and fertile offspring detected, a species can be defined with
absolute certainty.
C. a species can be definitively described by DNA hybridization, DNA sequencing, or enzymes.
D. just as organisms recognize their own species, all levels of taxa [class, order, family, genus] are naturally
occurring entities.
E. None of the choices is correct.
39. Based on the text's coverage of the rate of mutation, adaptive radiation, etc., you can conclude that the rate
of evolution progresses at
A. a fairly constant rate and would produce the same outcome if "re-run."
B. an uneven rate but would produce the same outcome if "re-run."
C. a fairly constant rate but would produce different outcomes if "re-run."
D. an uneven rate and would produce different outcomes if "re-run."
40. The Greek root words meaning "together" and "fatherland" are the basis for the term
A. prezygotic.
B. adaptive radiation.
C. speciation.
D. allopatric.
E. sympatric.
41. Microevolution is due to
A. genetic Flow.
B. gene mutations.
C. genetic drift.
D. non-random mating.
E. All of the choices apply.
42. All of the following are true statements regarding mating EXCEPT
A. random mating is due to chance pairing not according to genotype or phenotype.
B. sexual selection occurs when males compete for reproduction rights and females select mates based on a
particular phenotype.
C. short people tending to mate with tall people is an example of assortative mating.
D. All of the statements are true.
43. Types of natural selection for a particular trait include all of the following EXCEPT
A. founder effect.
B. directional selection.
C. stabilizing selection.
D. disruptive selection.
44. Variations within a population are maintained by
A. mutation.
B. genetic recombination due to fertilization.
C. gene flow.
D. All of the choices are correct.
45. Reproductive isolation mechanisms for a species include all of the following EXCEPT
A. habitat isolation
B. temporal isolation of reproduction
C. mechanical isolation of copulation
D. hybrid sterility
E. All of the choices are mechanisms.
46. In speciation which of the following is miss-matched?
A. allopatric speciation–geographic isolation
B. sympatric speciation–geographic isolation
C. adaptive radiation–chance for new species to adapt to new habitats
D. post-zygotic isolation–hybrid offspring sterility
47. A population of organisms that reproduce asexually without gametes from other individuals will display
more variation than a population that reproduces sexually using gametes from other individuals.
True False
48. Male birds often perform a special dance or set of physical displays to attract females. This would be an
example of a behavioral isolation mechanism.
True False
49. The bottleneck effect is thought to be responsible for the loss of variability and loss of fertility in the
cheetah species.
True False
50. Industrial melanism in peppered moths in England is an example of stabilizing selection.
True False
51. Sexual selection is a form of natural selection that does not cause adaptation to the environment.
True False
52. Gene mutation occurs at any time, without respect to the mutation's adaptive value or benefit to the
True False
53. The gene pool is described in terms of gene frequencies in the population.
True False
54. The Hardy-Weinberg equilibrium is usually met in most populations in changing environments.
True False
55. Genetic drift produces changes in allele frequencies within a gene pool due to chance.
True False
56. An example of the founder effect is seen in populations such as the Amish in Pennsylvania, in which
unusual genes are found in large numbers in the isolated population.
True False
57. A reproductive isolation mechanism includes any structural, functional, or behavioral characteristic that
blocks reproductive ability.
True False
58. Microevolution is evolution that occurs within a population.
True False
59. An allele becomes the most common allele in a population by becoming the dominant allele.
True False
60. Three types of natural selection include directional, stabilizing and disruptive.
True False
61. Define microevolution and give an example of it.
62. Describe the conditions that must be met to produce the Hardy-Weinberg equilibrium.
63. Explain the development of drug resistance in bacteria.
64. Describe the effects of chromosome mutations and gene mutations on population genetics.
65. Describe the effects of recombination on population genetics.
66. Distinguish between inbreeding and assortative mating.
67. In 1989, geneticists at the University of Texas-Houston brought many fruit fly cultures down to a few
bottleneck events and allowed these populations to build back up again. When they measured the
morphological diversity of the flies, they found them to be more diverse in structure rather than more
uniform. Consider the explanation of the cheetah bottleneck and note that while the bottleneck may have
resulted in the loss of alleles from the population, no statement is made concerning any loss of morphological
A) Would a relatively uncommon recessive morphological trait in a large population be expressed very often? If
it survived a bottleneck event, would it be expressed more often?
B) What would be its chance of being expressed if it survived a bottleneck event and was now in a small inbred
C) Consider that in North America, English sparrows, guinea pigs, and the African honey bee have all survived
recent bottleneck events. Why might a decrease in genetic diversity not depress these highly successful
68. Describe the conditions under which genetic drift occurs, and give one example.
69. Describe and differentiate among the effects of stabilizing selection, directional selection, and disruptive
70. Often textbooks state that "maintenance of variation is beneficial because populations that lack variation
may not be able to adapt to new conditions and may become extinct." However, environments such as deserts
and ocean deeps provide little variation and have changed little over thousands of years. And other organisms
are mobile and can easily move to an appropriate environment in front of slow-moving glaciers, etc. Instead,
focus on the internal environment each organism must sustain.
A) Do all people have equal resistance to microorganisms and viruses? Examples?
B) Would the rapid evolution of new strains of bacterial and viral disease agents promote or depress
polymorphism in human host populations? Why?
Chapter 18 KEY
1. B
2. D
3. C
4. C
5. E
6. C
7. C
8. D
9. C
10. B
11. A
12. E
13. C
14. E
15. B
16. E
17. D
18. D
19. A
20. C
21. B
22. A
23. B
24. D
25. B
26. D
27. A
28. E
29. D
30. A
31. C
32. C
33. E
34. D
35. D
36. B
37. D
38. E
39. D
40. E
41. E
42. C
43. A
44. D
45. A
46. B
48. TRUE
49. TRUE
51. TRUE
52. TRUE
53. TRUE
55. TRUE
56. TRUE
57. TRUE
58. TRUE
60. TRUE
61. Answers will vary.
62. Answers will vary.
63. Answers will vary.
64. Answers will vary.
65. Answers will vary.
66. Answers will vary.
67. Answers will vary.
68. Answers will vary.
69. Answers will vary.
70. Answers will vary.
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