Chapter 20—The Genetic Analysis of Populations and How They Evolve
Fill in the Blank
1. Genetic variation that affects the organism's characteristics is the basis for ______
selection.
Ans: natural
Difficulty: 1
2. Wild-type and heterozygous individuals of a ________ disease show normal
phenotypes.
Ans: recessive
Difficulty: 1
3. Changes in gene frequencies within populations are termed __________.
Ans: microevolution
Difficulty: 1
4. New species formation through slow changes in the existing organisms which take very
long periods of time is called as ____________.
Ans: macroevolution
Difficulty: 1
5. _________ for a given environment increases as the likelihood of survival and
reproduction of a certain type of organism increases.
Ans: fitness
Difficulty: 2
6. A large part of the variation in a naturally occurring population can be largely accounted
by ________ alone.
Ans: mutation
Difficulty: 2
7. If the likelihood that an individual will grow into an adult does not depend on the
genotype, then the allele frequencies in the adults should be the same as in their
_______.
Ans: gametes
Difficulty: 2
8. The binomial equation representing the ______-_________ proportions is p2 + 2pq +q2
= 1.
Ans: Hardy-Weinberg
Difficulty: 2
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9. _______ frequencies do not change from generation to generation in a population at
Hardy-Weinberg equilibrium.
Ans: Allele
Difficulty: 1
10. A single generation of selection will eliminate a lethal ________ allele from the
population.
Ans: dominant
Difficulty: 2
11. Allele frequency is affected by mutation and selection in ________ directions.
Ans: opposing
Difficulty: 2
12. New diseases emerge in human populations as a consequence of new _________.
Ans: mutations
Difficulty: 2
13. _______ relatedness of two individuals is the average fraction of common alleles at all
gene loci that the individuals share because they inherited them from a common
ancestor.
Ans: genetic
Difficulty: 3
14. The heritability of a trait _________ as the proportion of environmental variation
increases.
Ans: decreases
Difficulty: 2
15. The strength of selection and the heritability of a trait directly determine the trait's rate
of ________ in each generation.
Ans: evolution
Difficulty: 2
Multiple Choice
16.
A)
B)
C)
D)
E)
A population is a group of individuals of a species which:
interbreed.
reside in the same area.
inhabit the same space at the same time.
only b and c are true
a, b, and c are true
Ans: E
Difficulty: 1
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17.
A)
B)
C)
D)
E)
The sum total of all alleles carried in all members of a population is called its:
gene pool.
genome.
ploidy.
polygenic sum.
polymorphism.
Ans: A
Difficulty: 1
18.
A)
B)
C)
D)
E)
Microevolution is defined as:
a process that includes new species formation.
changes in the frequency of alleles within a population.
evolution of microorganisms.
interactions between species.
all of the above
Ans: B
Difficulty: 1
19.
A)
B)
C)
D)
E)
Macroevolution is defined as:
evolution that occurs over geologic time.
process by which new species emerge from existing species.
the consequence of extended periods of microevolution.
the origin of new species by mutation and natural selection.
all of the above
Ans: E
Difficulty: 2
20.
A)
B)
C)
D)
E)
Population genetics provides answers for all of the following questions except:
what is the frequency of genetic disease in a population?
what fraction of the phenotypic variation in a trait is the result of genetic variation?
what alleles are most likely to mutate?
given certain quantifiable variables, how long is a disease likely to persist?
how rapidly can a disease gain a foothold in a population?
Ans: C
Difficulty: 3
21.
A)
B)
C)
D)
E)
Which of the following is not one of the assumptions of the Hardy-Weinberg law ?
The population is very large.
There is non-random mating within the population.
Mutations in the alleles do not occur.
No migration occurs into or out of the population.
The ability of all genotypes for survival and reproduction is the same.
Ans: B
Difficulty: 2
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22.
A)
B)
C)
D)
E)
Hardy-Weinberg equilibrium in populations is defined as conditions which produce:
only heterozygotes.
many lethal alleles.
genetic drift.
constant allele frequencies which do not change from generation to generation.
all of the above
Ans: D
Difficulty: 2
23. The heterozygote genotype frequency term for a gene with two alternate alleles A
(frequency p) and a (frequency q) in the Hardy-Weinberg equation is:
A) p2.
B) q2.
C) 2pq.
D) (p+q)2.
E) p+q.
Ans: C
Difficulty: 1
24. If in a population of 1 million people, 100 albinos (homozygous recessives, aa) were
found, how many normal (homozygous dominants, AA) individuals will be found in the
next generation under equilibrium conditions?
A) 19,800
B) 100,000
C) 980,010
D) 999,900
E) 100
Ans: C
Difficulty: 4
25. In humans, brachydactyly is a dominant condition. Six thousand four hundred people in
a population of 10,000 show the disease (1,600 are BB, 4,800 are Bb) and 3,600 are
normal phenotypes (bb). The frequency of the b allele is:
A) 0.6.
B) 0.4.
C) 0.36.
D) 0.48.
E) 0.16.
Ans: A
Difficulty: 3
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26. The frequency of the Hemoglobin A allele is 0.9. The heterozygote with the recessive
allele, s, show resistance to the malarial parasite. What is the frequency of the
heterozygote for the pair As?
A) 0.81
B) 0.1
C) 0.01
D) 0.18
E) 0.09
Ans: D
Difficulty: 3
27. The genotypic frequency of inheriting autosomal recessive condition, phenylketonuria,
is 1 in 3,600 people. The frequency of the normal allele is:
A) 0.0167.
B) 0.9833.
C) 0.0328.
D) 0.00286.
E) 3,599.
Ans: B
Difficulty: 4
28.
A)
B)
C)
D)
E)
Which of the following is not generally true about conditions of natural populations?
Size is not always very large.
Individuals do not mate at random.
New mutations do occur.
There is migration in and out of the population.
Different genotypes have the same fitness.
Ans: E
Difficulty: 1
29.
A)
B)
C)
D)
E)
Fitness is described as:
an individual's ability to survive to adulthood.
an individual's ability to reproduce.
the effect of the particular genotype which cannot always be predicted.
a, b, and c are true.
only a, and b are true.
Ans: D
Difficulty: 1
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30. Changes in allele frequency in conditions of either natural or artificial selection depends
on:
A) allele frequencies themselves.
B) relative fitness related to viability.
C) reproductive abilities of the different phenotypes.
D) a, and b only.
E) a, b, and c.
Ans: D
Difficulty: 1
31. Many human recessive genetic diseases are maintained despite continuing selection
against them because:
A) heterozygotes have a higher fitness than either homozygote.
B) the recessive alleles mutate to dominant type.
C) there is no inheritance for the recessive allele.
D) the dominant allele frequency remain the same over generations.
E) none of the above.
Ans: A
Difficulty: 1
32.
A)
B)
C)
D)
E)
A disease which has been studied in great detail for heterozygote superiority is:
brachydactyly.
sickle cell disease.
insulin-dependent diabetes.
albinism.
tuberculosis.
Ans: B
Difficulty: 1
33. If African populations have a relative fitness of the wild type genotype of 0.8, and that
of the heterozygote of 1.0, then the relative advantage in fitness of the heterozygotes
would be:
A) 0.8.
B) 0.08.
C) 0.16.
D) 0.28.
E) 1.25.
Ans: E
Difficulty: 2
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34.
A)
B)
C)
D)
E)
Mutations arise from:
DNA damage due to environmental agents.
from errors in replication.
from errors in transmission of genetic information in cell division.
only a and b.
a, b, and c.
Ans: E
Difficulty: 1
35.
A)
B)
C)
D)
E)
Frequency of disease alleles is influenced by:
heterozygous advantage.
mutation.
time of onset of disease.
selection.
all of the above.
Ans: E
Difficulty: 1
36. Unpredictable, chance fluctuation in allele frequency that have a neutral effect on fitness
is called:
A) founder effect.
B) selection.
C) genetic drift.
D) mutation.
E) inbreeding.
Ans: C
Difficulty: 1
37.
A)
B)
C)
D)
E)
The process in which rare alleles increase in frequency in a new population is known as:
gene flow.
genetic drift.
founder effect.
inbreeding.
selection.
Ans: C
Difficulty: 2
38.
A)
B)
C)
D)
E)
Diseases persist because:
changes in allele frequency tend toward evolutionary equilibrium.
mutation balances selection.
the alleles become dominant.
only a and b.
a, b, and c.
Ans: D
Difficulty: 2
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39.
A)
B)
C)
D)
E)
The factors contributing to the antibiotic resistance of bacterial pathogens are:
patient noncompliance with drug treatments.
strong selection imposed by antibiotic increases the rate of evolution in each generation.
plasmids provide a means for the genetic exchange of resistance genes.
only b and c.
a, b and c.
Ans: E
Difficulty: 1
40. Development of Insulin-dependent diabetes is associated with how many separate
regions of the human genome?
A) 12
B) 10
C) 8
D) 6
E) 4
Ans: A
Difficulty: 1
41.
A)
B)
C)
D)
E)
Multifactorial traits:
are affected by both genetic and environmental factors.
are continuous.
vary over a continuous range of measurements.
are affected by environmental factors such as penetrance and expressivity.
all of the above.
Ans: E
Difficulty: 2
42.
A)
B)
C)
D)
E)
The total phenotype variance (VP) is:
the sum of genetic variance (VG) and environmental variance (VE).
the difference between VG and VE.
not dependent on VG.
not dependent on VE.
always constant.
Ans: A
Difficulty: 2
43.
A)
B)
C)
D)
E)
Heritability is defined as:
VG.
VP.
VE.
VG/VP.
VP/VG.
Ans: D
Difficulty: 3
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44.
A)
B)
C)
D)
E)
The total genetic relatedness of two siblings is:
2.
1.
0.5.
0.2.
none of the above.
Ans: C
Difficulty: 2
45.
A)
B)
C)
D)
E)
Which of the following is not true about monozygotic twins.
They share all alleles at all loci.
They have a genetic relatedness of 0.5.
They have a genetic relatedness of 1.
They come from the joining of a single egg with a single sperm cell.
They are the result of a split of the zygote after fertilization.
Ans: B
Difficulty: 1
46.
A)
B)
C)
D)
E)
Recent heritability studies on twins show that there is a genetic component to:
memory.
extroversion.
verbal reasoning.
a, b, and c.
only a and b.
Ans: D
Difficulty: 1
47.
A)
B)
C)
D)
E)
The response to selection, R, is equal to:
the heritability (h2) of a trait.
the strength (S) of selection.
the difference between h2 and S.
S/h2.
h2S.
Ans: E
Difficulty: 2
48. A number of interacting genes produce quantitative inheritance. The transmission of
these genes can be seen in the phenotypical pattern of:
A) discontinuous distribution of discrete phenotypes.
B) continuous variation in phenotypic expression.
C) strict dominance and recessiveness.
D) all of the above.
E) only a and b.
Ans: B
Difficulty: 2
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49. A cross between a tall and a short pea plant produced intermediate height in the F1
generation. When the F1s were crossed plants of the original parental heights and plants
with a range of heights in between the extremes were produced. The mode of
inheritance is described as:
A) multifactorial.
B) independent assortment.
C) incomplete dominance.
D) codominance.
E) segregation.
Ans: A
Difficulty: 1
50.
A)
B)
C)
D)
E)
Multifactorial inheritance is observed in phenotypes which show typically:
only one discrete type.
two extremes.
a bell shaped distribution.
a higher mutation rate.
all of the above.
Ans: C
Difficulty: 1
51.
A)
B)
C)
D)
E)
Continuous traits are:
due to sex-linked genes only.
due to autosomal genes only.
qualitative in nature.
quantifiable in measurements.
result of test-crosses only.
Ans: D
Difficulty: 1
52.
A)
B)
C)
D)
E)
In addition to genetic factors, environmental factors influence the inheritance of:
metabolic diseases.
recessive diseases.
dominant diseases.
sex-linked diseases.
polygenic traits.
Ans: E
Difficulty: 2
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53. Brown insects living in a dark background survived in a ratio of 90/120, while the same
insects in a lighter background survived in a ratio of 30/120. The ratio of relative fitness
of the insects in dark to lighter background is:
A) 1 : 0.333.
B) 0.75 : 0.25.
C) 90 : 120.
D) 3 : 1.
E) none of the above.
Ans: A
Difficulty: 4
54. If the relative fitness of genotypes MM, MN, NN are 0.8, 1.0, and 0.2 respectively, the
expected equilibrium frequency of N is:
A) 0.8.
B) 1.0.
C) 0.2.
D) 1.25.
E) 4.0.
Ans: C
Difficulty: 4
55.
A)
B)
C)
D)
E)
Twins made from two individual zygotes (dizygotic twins):
are related genetically as the monozygotic twins.
share 0% genetic similarities.
are similar in 100% of genetic sequences.
are related genetically as non-twin siblings.
are similar to parents.
Ans: D
Difficulty: 2
56.
A)
B)
C)
D)
E)
An increase in fitness is described as:
migrating to a new environment.
successful adaptation.
being successful in producing many offspring.
exhibiting new traits.
mutating to a dominant trait.
Ans: B
Difficulty: 2
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57. The frequencies of ABO blood groups in a certain population are: A=0.22, B=0.44,
AB=0.18, and O=0.16. The frequency of the O allele in the population is:
A) 0.469.
B) 0.663.
C) 0.424.
D) 1.0.
E) 0.4.
Ans: E
Difficulty: 3
58. Under special circumstances, migration does not change allele frequencies. If the allele
frequencies of a dominant and recessive allele are both 0.5, then migration of which of
the following will not change the frequencies of the alleles?
A) homozygous recessive individuals
B) haploid individuals
C) diploid individuals
D) heterozygous individuals
E) homozygous dominant individuals
Ans: D
Difficulty: 3
Matching
Match the following terms with the best definition
a. genetic drift
b. adaptation
c. natural selection
d. fitness
e. polymorphism
59. The presence of many alleles of a gene in a population.
Ans: e
Difficulty: 2
60. Genetic contributions of an individual to succeeding generations.
Ans: d
Difficulty: 2
61. Change in structure, behavior or physiology that promotes the likelihood of the
organism's survival in a specific environment.
Ans: b
Difficulty: 2
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62. The suitability of at least one genotype at every generation in varied environmental
conditions.
Ans: c
Difficulty: 2
63. Chance, random change in the frequency of an allele at a locus.
Ans: a
Difficulty: 2
Match the following terms with the best definition
a. heterozygous advantage
b. response to selection
c. population
d. gene pool
e. founder effect
f. heritability
64. All alleles carried in all members of population.
Ans: d
Difficulty: 2
65. A group of interbreeding individuals of the same species.
Ans: c
Difficulty: 2
66. Occurs when a few individuals separate from a larger population and establish a new
one that coexists with the original population.
Ans: e
Difficulty: 2
67. The proportion of total phenotypic variance ascribable to genetic variance.
Ans: f
Difficulty: 2
68. The property that maintains many recessive genetic diseases despite continuous
selection against them.
Ans: a
Difficulty: 2
69. The term which takes into account both the strength of selection, and the heritability of a
trait. It is also the amount of evolution.
Ans: b
Difficulty: 2
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True or False
70. The definition of allele frequency is the proportion of all copies of a given gene in a
population that are of a specific allele type with the total gene number equal to two
times the number of individuals in the population.
Ans: True
Difficulty: 1
71. Derivations of the Hardy-Weinberg law depends on five assumptions regarding the
nature of the population in question, including that there is no migration into or out of
the population.
Ans: True
Difficulty: 1
72. The binomial Hardy-Weinberg equation is represented by p2 + p2q2 + q2 = 1.
Ans: False
Difficulty: 2
73. A population that achieves genotype frequencies of p2, 2pq, and q2 in just one
generation and remains at these frequencies, is said to be in Hardy-Weinberg
equilibrium.
Ans: True
Difficulty: 1
74. Macroevolution is the drastic change of allele frequency in a population in a single
generation.
Ans: False
Difficulty: 2
75. Fitness is the term that geneticists use to describe an individual's relative ability to
survive and transmit genes to the next generation.
Ans: True
Difficulty: 1
76. Heterozygous advantage to a disease state is sometimes responsible for the retention of
recessive genes that otherwise reduce fitness under normal conditions.
Ans: True
Difficulty: 1
77. Genetic drift has a predictable effect on evolution which scientists can easily calculate.
Ans: False
Difficulty: 2
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78. The founder effect may lead to a higher incidence of certain alleles than seen in large
diverse populations.
Ans: True
Difficulty: 1
79. The evolution of drug resistance in bacteria results from several factors including, short
generation time, large populations which ensure incidence of mutations, strong selection
by drug and the variety of ways by which bacteria can acquire new genetic diversity.
Ans: True
Difficulty: 1
80. Selection for resistance in the presence of pesticides is the only factor that influences the
rate of resistance among pest populations.
Ans: False
Difficulty: 2
81. Complex traits that are multifactorial are continuous. They are also called quantitative
traits because they vary over a continuous range of measurement.
Ans: True
Difficulty: 1
82. Heritability is the proportion of total phenotypic variance due to genetic variance.
Ans: True
Difficulty: 1
83. One way scientists attempt to control confounds due to environmental variability is to
cross-foster.
Ans: True
Difficulty: 1
84. When a trait has a large heritability, it is primarily genetically determined and thus,
unaffected by the environment.
Ans: False
Difficulty: 2
Short Answer
85. What is migration? How does it affect Hardy-Weinberg equilibrium?
Ans: Migration is the movement of individuals from one population to another. It
results in a change in the frequency of each population. This change translates into
allele frequencies which are no longer constant from generation to generation as
predicted by the Hardy-Weinberg equilibrium.
Difficulty: 2
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86. What is genetic drift? Is it dependent on the size of the population?
Ans: Chance fluctuation in allele frequency is called genetic drift. It affects small
populations because the loss of a single individual of a given genotype will
drastically alter the gene frequencies of the remainder of the population.
Difficulty: 3
87. How does the founder effect dictate the genetic composition of the new population?
Ans: The founders of a new population are the sole source of alleles of a given gene.
Therefore the genetic composition is entirely dependent on the allele types of the
founders which typically interbreed within themselves and tend to conserve the
alleles found in the originators.
Difficulty: 2
88. What is selection? How does it alter allele frequencies?
Ans: Selection is the process by which individual organisms are selected for survival
and reproduction. The offspring contain the parental genetic information. The
more successful organisms will leave more offspring and hence more of their
genes and hence alleles of the parental types in the generations to come.
Difficulty: 3
89. Explain QTLs.
Ans: They refer to the genes which control the expression of quantitative traits. They
are shorthand for quantitative trait loci.
Difficulty: 1
90. Relate genetic variance (VG) and phenotypic variance (VP) to heritability.
Ans: Heritability h2 = VG/VP.
Difficulty: 2
91. What are the components of phenotypic variance?
Ans: VP = VG + environmental variance.
Difficulty: 3
92. Define a population in genetic terms?
Ans: A population is a group of interbreeding individuals of the same species that
inhabit the space at the same time.
Difficulty: 1
93. What is the difference between phenotype frequency, genotype frequency and allele
frequency?
Ans: Phenotype and genotype frequency are the proportion of individuals in a
population that show a particular phenotype or have a particular genotype
respectively while allele frequency is the proportion of all copies of a gene in a
population that are of a given allele type.
Difficulty: 2
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94. Derivation of the Hardy-Weinberg law depends on what five assumptions?
Ans: 1. The population includes a very large, virtually infinite number of individuals.
2. The individuals mate at random. 3. No new mutations appear in the gene pool.
4. There is no migration into or out of the population. 5. There are no genotypedependent differences in the ability to survive to reproductive age and transmit
genes to the next generation.
Difficulty: 3
95. What is the difference between natural and artificial selection?
Ans: Natural selection is the progressive elimination of individuals whose fitness is low
and the reproduction of individuals with highest fitness. Artificial selection is
similar to natural selection in that low fitness individuals can be selected against
but in this case matings are controlled and desired selection is deliberate.
Difficulty: 2
96. List five forces that change the frequency of an allele in a population and discuss why
the elimination of a deleterious recessive allele is nearly impossible.
Ans: Allele frequency is altered by genetic drift, migration, mutation, natural selection,
and nonrandom mating. Elimination of a deleterious recessive allele is nearly
impossible because in the heterozygous state there is no negative selection against
it so it commonly remains an uncommon allele in a population. Also, for some
alleles there is heterozygous advantage which will contribute to selection for a
deleterious recessive allele.
Difficulty: 4
Experimental Design and Interpretation of Data
97. How would studies on monozygotic and dizygotic twins help in the understanding of
genetic basis of behavior in humans?
Ans: The degree to which variation in human behavior is determined by genetic
inheritance can be studied by observing monozygotic twins under the same and
different environmental conditions. Dizygotic twins on the other hand if grown in
similar environments like the same household can yield valuable insights into the
effect of heredity on behavioral characteristics.
Difficulty: 3
98. How can a value of 1.0 for h2 can be interpreted?
Ans: It means that almost all of the phenotypic variation is due to inheritance.
Difficulty: 4
99. Explain why a population carries more genetic diversity than an individual?
Ans: In the case of multiple alleles such as the ABO blood group system the greatest
number of alleles an individual can carry is 2 while many can be carried by the
population.
Difficulty: 4
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100. A gene in a natural population of prairie dogs has three alleles, which can be determined
by electrophoretic analysis following PCR amplification. The respective bands are 170,
200, and 230 base pairs in size. You have genotyped 1,000 animals and found the
following frequencies for the six different genotypes: 170/170=0.06, 200/200=0.58,
230/230=0.04, 170/200=0.20, 170/230=0.02, 200/230=0.10. What are the allele
frequencies? Is the population in Hardy-Weinberg Equilibrium?
Ans: f(170)= 0.06 + ½ (0.20) + ½ (0.02) = 0.17
f(200)= 0.58 + ½ (0.20) + ½ (0.10) = 0.73
f(230)= 0.04 + ½ (0.02) + ½ (0.10) = 0.10
(p + q + r)2 = p2 + q2 + r2 + 2pq + 2pr + 2qr = 0.03 + 0.53 + 0.01 + 0.25 + 0.03
+ 0.15
This is not what is observed therefore, the population is NOT in equilibrium.
Difficulty: 4
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