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Microevolution (Ch 16) Test Bank
Multiple Choice
Identify the letter of the choice that best completes the statement or answers the question.
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1. Which of the following statements describes what all members of a population share?
a. They are temporally isolated from one another.
b. They are geographically isolated from one another.
c. They are members of the same species.
d. They have identical genes.
2. Which statement about gene pools is typically true?
a. They contain two or more alleles for each gene.
b. They contain only dominant alleles.
c. They belong to two or more interbreeding species.
d. The relative frequencies of the alleles never change.
3. If an allele makes up one fourth of a population’s alleles for a given trait, its relative frequency is
a. 100 percent.
c. 25 percent.
b. 75 percent.
d. 4 percent.
4. In many kinds of organisms, most heritable differences are due to
a. mutations during gamete formation.
b. chemicals in the environment.
c. gene shuffling during gamete formation.
d. the effects of radiation.
5. Gene shuffling includes the independent movement of chromosomes during meiosis as well as
a. mutations from radiation.
b. changes in the frequencies of alleles.
c. crossing-over.
d. mutations from chemicals.
6. A single-gene trait that has two alleles and that shows a simple dominant-recessive pattern will result in
a. one phenotype.
c. four phenotypes.
b. two phenotypes.
d. millions of phenotypes.
7. When individuals at only one end of a bell-shaped curve of phenotype frequencies have high fitness, the result
is
a. directional selection.
c. disruptive selection.
b. stabilizing selection.
d. genetic drift.
8. When individuals with an average form of a trait have the highest fitness, the result is
a. not predictable.
c. directional selection.
b. disruptive selection.
d. stabilizing selection.
9. Genetic drift tends to occur in populations that
a. are very large.
b. are small.
c. are formed from new species.
d. have unchanging allele frequencies.
10. The type of genetic drift that follows the colonization of a new habitat by a small group of individuals is
called
a. the Hardy-Weinberg principle.
c. directional selection.
b. the founder effect.
d. stabilizing selection.
11. The genetic equilibrium of a population can be disturbed by each of the following EXCEPT
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a. nonrandom mating.
b. movement into and out of the population.
c. a large population size.
d. mutations.
The allele frequencies of a population are more likely to remain unchanged if
a. the population size is reduced.
b. frequent movement into and out of the population occurs.
c. all mating is random.
d. the mutation rate increases.
What situation might develop in a population having some plants whose flowers open at midday and other
plants whose flowers open late in the day?
a. behavioral isolation
c. temporal isolation
b. geographic isolation
d. genetic drift
The Galápagos finch species are an excellent example of
a. speciation.
c. stabilizing selection.
b. genetic equilibrium.
d. selection on single-gene traits.
What did Peter and Rosemary Grant learn about mate choice in the Galápagos finches?
a. Phenotype plays no role in mate choice.
b. Genotype plays no role in mate choice.
c. Finches prefer mates with smaller beaks than their own.
d. Finches prefer mates with beaks similar in size to their own.
The combined genetic information of all members of a particular population is the population’s
a. relative frequency.
c. genotype.
b. phenotype.
d. gene pool.
A change in a sequence of DNA is called a
a. recombination.
c. single-gene trait.
b. polygenic trait.
d. mutation.
The two main sources of genetic variation are
a. genotypes and phenotypes.
b. gene shuffling and mutations.
c. single-gene traits and polygenic traits.
d. directional selection and disruptive selection.
An example of a single-gene trait is
a. a widow’s peak in humans.
b. the weight of human infants at birth.
c. height in humans.
d. beak size in the Galápagos finches.
The number of phenotypes produced for a given trait depends upon
a. the number of genes that control the trait.
b. which form of the trait is dominant.
c. the relative frequencies of the various alleles.
d. whether or not natural selection is at work.
The distribution of phenotypes for a typical polygenic trait can often be expressed as
a. a bar graph.
c. Mendelian ratios.
b. a bell-shaped curve.
d. allele frequencies.
Natural selection acts directly on
a. alleles.
c. phenotypes.
b. genes.
d. mutations.
____ 23. Which of the following is NOT a way in which natural selection affects the distribution of phenotypes?
a. directional selection
c. disruptive selection
b. stabilizing selection
d. chance events
____ 24. In genetic drift, allele frequencies change because of
a. mutations.
c. natural selection.
b. chance.
d. genetic equilibrium.
____ 25. Which of the following events do biologists consider a random change?
a. directional selection
c. disruptive selection
b. speciation
d. genetic drift
____ 26. The situation in which allele frequencies of a population remain constant is called
a. evolution.
c. genetic equilibrium.
b. genetic drift.
d. natural selection.
____ 27. One of the conditions required to maintain genetic equilibrium is
a. natural selection.
b. mutations.
c. nonrandom mating.
d. no movement into or out of the population.
____ 28. The separation of populations by barriers such as rivers, mountains, or bodies of water is called
a. temporal isolation.
c. behavioral isolation.
b. geographic isolation.
d. genetic equilibrium.
____ 29. A factor that is necessary for the formation of a new species is
a. reproduction at different times.
b. geographic barriers.
c. different mating behaviors.
d. reproductive isolation.
____ 30. Which is the first step that occurred in the speciation of the Galápagos finches?
a. establishment of genetic equilibrium
c. ecological competition
b. behavioral isolation
d. arrival of the founding population
Completion
Complete each sentence or statement.
31. Crossing-over can occur during the meiotic divisions that produce cells called ____________________.
32. A polygenic trait can have many possible genotypes and ____________________.
33. When the phenotypes of polygenic traits are represented by a bell-shaped curve, the ____________________
of individuals close together on the curve is not very different.
34. When a population is NOT evolving, it is in a situation called _________________________.
35. In the Galápagos finches that Rosemary and Peter Grant studied, a pattern of natural selection called
____________________ selection favored individuals with larger, heavier beaks during a drought.
36. A gene pool typically contains two or more ____________________ for each gene.
37. Inheritable traits can be classified as either ____________________ traits or polygenic traits.
38. For ____________________ traits, natural selection can affect the distribution of phenotypes in three ways.
39. According to the _________________________ principle, allele frequencies in a population will remain
constant unless one or more of five specific factors cause those frequencies to change.
40. For new species to evolve, populations must be ____________________ isolated from each other.
Short Answer
41. Would a trait that has only two distinct phenotypes more likely be a single-gene trait or a polygenic trait?
How do you know?
42. Is an allele for a trait that has no effect on a species’ fitness affected by natural selection? Explain.
43. List the five conditions necessary to maintain genetic equilibrium in a population.
44. Why might a geographic barrier such as a large river cause the formation of a new species of small rodents
but not a new species of birds?
45. How does the work of Peter and Rosemary Grant in the Galápagos relate to the work of Charles Darwin?
46. Are the members of a population necessarily the same species? Explain.
47. What are the two main sources of genetic variation? Which of them is more common?
48. Explain how stabilizing selection would affect a graph of the distribution of phenotypes for a trait.
49. Why might genetic drift occur if a small number of individuals colonized a new habitat?
50. What are three mechanisms for reproductive isolation? Which mechanism isolates two populations of similar
frogs with different mating calls?
Modified True/False
Indicate whether the sentence or statement is true or false. If false, change the identified word or phrase to make the
sentence or statement true.
____ 51. Because all members of a population can interbreed, biologists often study their genes as a single group.
_________________________
____ 52. In a gene pool, as the relative frequency of one allele for a trait increases, the relative frequencies of other
alleles for that trait decrease. _________________________
____ 53. Most inheritable differences are due to mutations that occur during the production of gametes.
_________________________
____ 54. Mutations do not always affect an organism’s genotype—its physical, behavioral, and biochemical
characteristics. _________________________
____ 55. A polygenic trait is controlled by one gene. _________________________
____ 56. On a graph, the distribution of phenotypes for a single-gene trait tends to form a bell-shaped curve.
_________________________
____ 57. Natural selection on single-gene traits can lead to changes in allele frequencies.
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____ 58. In a population of snakes with a range of body lengths, if the longest individuals have the highest fitness,
disruptive selection is likely to occur. _________________________
____ 59. In small populations, an allele can become more or less common simply by chance.
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____ 60. Genetic drift may occur when a small group of individuals colonize a new habitat.
_________________________
____ 61. When mutations introduce new alleles into a population, genetic variation is disrupted.
_________________________
____ 62. In a population of birds, if females prefer males with long tails, the population violates the condition of
directional selection described by the Hardy-Weinberg principle. _________________________
____ 63. In the type of reproductive isolation called behavioral isolation, two populations are separated by barriers
such as rivers or mountains. _________________________
____ 64. Two populations that have overlapping ranges can remain reproductively isolated through behavioral isolation
or temporal isolation from each other. _________________________
____ 65. The first step of the speciation of the Galápagos finches likely was the arrival of founders from South
America. _________________________
Other
USING SCIENCE SKILLS
Figure 16–1
66. Interpreting Graphics According to Graph A in Figure 16-1, what has occurred?
67. Interpreting Graphics According to Graph B in Figure 16-1, what has occurred?
68. Interpreting Graphics According to Graph C in Figure 16-1, what has occurred?
69. Inferring Which of the three graphs in Figure 16-1 might show a population of birds that specialize in
different types of food? Explain.
70. Inferring What factor or condition might have led to the change shown in Graph A of Figure 16-1?
USING SCIENCE SKILLS
Figure 16–2
71. Interpreting Graphics Describe the information about frog species that is shown in Figure 16-2.
72. Interpreting Graphics According to Figure 16-2, there is a brief period during which frog mating nearly
stops. When does this occur?
73. Inferring Based on Figure 16-2, what mechanism appears to keep bullfrogs reproductively isolated? Would
that mechanism necessarily be the only isolating mechanism? Explain.
74. Inferring Peeper frogs and leopard frogs do not interbreed even when they share a habitat. Use the
information in Figure 16-2 to determine what mechanism probably keeps the two species reproductively
isolated.
75.Predicting Frog mating does not occur in cold weather. Assume that the mating times shown in Figure 16-2 are for
frogs in the northern part of the United States. How might these curves change for frogs in the southern part
of the United States? Explain.
Figure 16–3
76. Applying Concepts Explain what speciation means using examples from Figure 16–3.
77. Designing Experiments Suppose that researchers suspected that two groups shown in Figure 16–3 were
actually a single species. How might the researchers test that hypothesis?
78. Applying Concepts Darwin found the bird species in Figure 16–3 on one or more of the Galápagos Islands.
How might the island geography have affected the evolution of these species?
79. Formulating Hypotheses Examine Figure 16–3 and observe the large ground finch and medium ground
finch. Assume that the diagram shows the average type of beak for each group. If these species were formed
from a single type of natural selection, which type is it most likely to be? Explain.
80. Interpreting Graphics Competition for resources plays a key role in natural selection. Describe one way that
competition for food might have influenced the evolution of the large tree finch.