23
The Mechanisms of Evolution
TEST FILE QUESTIONS
Fill in the Blank
1. Evolution is the accumulation of _______ changes within populations over time.
Answer: heritable
2. The frequencies of the variants at each locus in a population are called _______.
Answer: allele frequencies
3. The genetic expression of traits (e.g., “homozygous recessive”) is called the
organism’s _______.
Answer: genotype
4. The physical expression of a trait (e.g., height or eye color) describes an organism’s
_______.
Answer: phenotype
5. Short-term changes in a population’s gene pool are often referred to as _______.
Answer: microevolution
6. The _______ is the sum total of genetic information in a population at any given
moment. It includes every allele at every locus in every organism.
Answer: gene pool
7. The relative reproductive contribution of an individual to subsequent generations is
termed the individual’s
Answer: fitness
8. When individuals with intermediate values of traits have the highest fitness, _______
is said to be operating.
Answer: stabilizing selection
9. A population that is not changing (i.e., it has constant genotype and allele frequencies
Answer: equilibrium
10. _______ involves movement of individuals to a new location, followed by breeding.
Answer: Gene flow
11. The differential contribution of offspring resulting from different heritable traits is
called _______.
Answer: natural selection
12. The idea of natural selection is most closely associated with _______, who proposed
it in 1859 in his book The Origin of Species.
Answer: Charles Darwin
13. In a small population, a change in the allele frequencies that results from chance is
called _______.
Answer: genetic drift
14. Genetic drift can be brought about either by a severe reduction in population size,
known as a population _______, or by a small number of individuals’ establishing a new
population, which results in a _______.
Answer: bottleneck; founder effect
15. Populations of a European clover, Trifolium repens, produce cyanide, which increases
their resistance to herbivores such as mice and slugs; however, it also increases their
susceptibility to frost. Populations from northeast Europe produce relatively little cyanide
compared to populations in southwest Europe. Subpopulations vary genetically in this
way because they are subjected to different _______.
Answer: selective pressures
16. A _______ is a change in DNA sequence.
Answer: mutation
Multiple Choice
1. Assume that a population is in Hardy–Weinberg equilibrium for a trait controlled by
one locus and two alleles. If the frequency of the recessive allele is 0.90, what is the
frequency of the dominant allele?
a. 0.10
b. 0.19
c. 0.81
d. None of the above
e. This cannot be answered without more information.
Answer: a
2. There is a gene that causes people to have crumbly earwax. This gene is expressed as a
complete dominant: Individuals who are homozygous dominants (CC) or heterozygous
(Cc) have crumbly earwax. Homozygous recessives (cc) have gooey earwax. On Paradise
Island there are 100 people, 75 of whom have crumbly earwax. Assuming Hardy–
Weinberg conditions, what is the frequency of the c allele on Paradise Island?
a. 0.25
b. 0.50
c. 0.87
d. None of the above
e. This cannot be answered without more information.
Answer: b
3. In a population at Hardy–Weinberg equilibrium, the frequency of heterozygotes is
0.64. What is the frequency of the homozygous dominants?
a. 0.08
b. 0.64
c. 0.80
d. None of the above
e. This cannot be answered without more information.
Answer: e
4. In a population at Hardy–Weinberg equilibrium, the frequency of the a allele is 0.60.
What is the frequency of individuals heterozygous for the A gene?
a. 0.16
b. 0.24
c. 0.48
d. None of the above
e. This cannot be answered without more information.
Answer: c
5. There are five conditions that must be met for a population to be in Hardy–Weinberg
equilibrium. Which of the following is not one of those conditions?
a. Nonrandom mating
b. Large population size
c. No migration
d. No natural selection
e. No mutations
Answer: a
6. Which of the following populations would demonstrate a population bottleneck?
a. The population of El Paso, Texas, after it has moved in its entirety to Patagonia
b. Eight male and eight female elephant seals that have survived the wreck of the Exxon
Valdez
c. A million male orangutans
d. Six male orangutans collected from a natural population in Sumatra and moved to the
San Diego Zoo
e. None of the above
Answer: b
7. _______ is the effect produced when a bee carries pollen from one population to
another.
a. Gene flow
b. A population bottleneck
c. A founder event
d. Genetic equilibrium
e. Assortative mating
Answer: a
8. In a large population, mutation pressure in the absence of selection
a. probably has little effect on the gene pool.
b. produces major evolutionary changes.
c. is what has made us different from the dinosaurs.
d. is usually beneficial.
e. never occurs.
Answer: a
9. Which of the following is not true of mutation?
a. Mutation creates the raw material that makes evolution possible.
b. Most mutations are harmful or neutral.
c. Mutation rates are very low for most loci.
d. Mutations are a likely cause of deviations from Hardy–Weinberg proportions in a
population.
e. Mutations probably have little effect on the gene pool of a large population.
Answer: d
10. Over the long run, mutations are important to evolution because
a. they are the original source of genetic variation.
b. once an allele is lost through mutation, another mutation to that same allele cannot
occur.
c. most mutation rates are one in a thousand.
d. whether good or bad, mutations increase the fitness of an individual.
e. mutations are usually beneficial to the progeny.
Answer: a
11. _______ selection occurs when the extremes of a population contribute relatively few
offspring to the next generation as compared to average members of the
a. Corrective
b. Directional
c. Stabilizing
d. Disruptive
e. Natural
Answer: c
12. _______ selection occurs when one extreme of a population contributes more
offspring to the next generation than average members of the population do.
a. Corrective
b. Directional
c. Stabilizing
d. Disruptive
e. Natural
Answer: b
13. Which of the following agents of evolution adapts a population to its environment?
a. Nonrandom mating
b. Natural selection
c. Migration
d. Genetic drift
e. Mutation
Answer: b
14. The raw material for evolutionary change is _______ variation.
a. phenotypic
b. genetic
c. geographical
d. environmentally-induced
e. behavioral
Answer: b
15. A population evolves when
a. environmentally-induced variation is constant between generations.
b. individuals with different genotypes survive or reproduce at different rates.
c. the environment changes on a seasonal basis.
d. members reproduce by cloning.
e. juvenile and adult stages require different environments.
Answer: b
16. Selection acts on _______ variation; however, evolution depends on _______
variation.
a. phenotypic; genetic
b. genetic; phenotypic
c. genetic; environmentally-induced
d. environmentally-induced; phenotypic
e. environmentally-induced; genetic
Answer: a
17. Limpets growing high in the intertidal zone, where they experience heavy wave
action, are more conical than individuals of the same species growing in the subtidal
zone, where they are protected from waves. Individuals transplanted from the high
intertidal zone to the subtidal zone add new growth, which produces a flatter, subtidal
shape. This experiment suggests that the difference in
a. phenotypes is environmentally-induced.
b. genotypes is environmentally-induced.
c. phenotypes is genetically based.
d. genotypes is due to natural selection.
e. This cannot be answered without more information.
Answer: a
18. Which of the following is an example of environmentally-induced variation?
a. Water fleas grown in cool or calm water develop round heads. If they are moved to
warm or turbulent water, they develop pointed “helmets” on their heads.
b. Plants collected along an altitudinal cline vary in size when grown in their native
habitat, yet when grown in a greenhouse they are all the same size.
c. Limpets growing high in the intertidal zone, where they experience heavy wave action,
are more conical than individuals of the same species growing in the subtidal zone, where
they are protected from waves. Individuals transplanted from the high intertidal zone to
the subtidal zone add new growth, which produces a flatter, subtidal shape.
d. Leaves on the same tree or shrub often differ in shape and size. In oaks, leaves closer
to the top receive more wind and sunlight and are more deeply lobed than leaves lower
down.
e. All of the above
Answer: e
19–23. Suppose you have a population of flour beetles with 1,000 individuals. Normally
the beetles are a red color; however, this population is polymorphic for a mutant
autosomal body color, black, designated by b/b. Red is dominant to black, so B/B and B/b
genotypes are red. Assume the population is in Hardy–Weinberg equilibrium, with f(B) =
p = .5 and f(b) = q = .5.
19. What would be the expected frequencies of the red and black phenotypes?
a. .5 red, .5 black
b. .75 red, .25 black
c. .25 red, .75 black
d. None of the above
e. This cannot be answered without more information.
Answer: b
20. What would be the expected frequencies of the homozygous dominant, heterozygous,
and homozygous recessive after 100 generations if the population is under the conditions
of Hardy–Weinberg?
a. .75, .20, .05
b. .25, .5, .25
c. All red, because it is the natural color
d. All black, because all red alleles would mutate to black
e. .5, .2, .3
Answer: b
–Weinberg
conditions were met, except that 1,000 black individuals migrated into the population?
a. .75, .25
b. .25, .75
c. .5, .5
d. They would not change because the population would still be in Hardy–Weinberg
equilibrium.
e. None of the above
Answer: b
22. What would be the allele frequencies if a population bottleneck occurred and only
four individuals survived: one female red heterozygote and three black males?
a. .875, .125
b. .125, .875
c. .25, .75
d. .75, .25
e. .5, .5
Answer: b
23. If the population in the previous question mated randomly, what would be the allele
frequencies of their offspring?
a. .875, .125
b. .125, .875
c. .25, .75
d. .75, .25
e. .5, .5
Answer: b
24. A gene pool consists of all the alleles
a. of an individual’s genotype.
b. present in a specific population.
c. that occur in a species throughout its evolutionary existence.
d. that contribute to the next generation of a population.
e. of a biome.
Answer: b
25. An important feature of sexual reproduction is that it
a. is unique to animals.
b. produces variation through genetic recombination.
c. uses mitosis in producing gametes.
d. is more efficient than asexual reproduction.
e. is always associated with selective mating.
Answer: b
26. In a West African finch species, birds with large or small bills survive better than
birds with intermediate-sized bills. The type of natural selection operating on these bird
populations is _______ selection.
a. directional
b. disruptive
c. stabilizing
d. nonrandom
e. deme
Answer: b
27–28. Hardy–Weinberg frequencies for the three genotypes AA, Aa, and aa, at all values
of p and q, are shown below.
27. As the frequency of the homozygous recessive genotype increases, the frequency of
the
a. heterozygous genotype decreases continuously.
b. homozygous dominant increases.
c. heterozygous genotype increases continuously.
d. dominant allele approaches 1.
e. recessive allele approaches 1.
Answer: e
28. Which of the following is supported by the graph above?
a. When aa = 0.45, Aa = 0.45.
b. When aa = 0.16, q = 0.60.
c. When p = 0.33, q = 0.77.
d. When Aa = 0.49, p = 0.70.
e. When AA = 0.50, aa = 0.
Answer: a
29. In a population of organisms, the frequency of the heterozygous genotype is always
a. greater than the frequency of the homozygous recessive genotype.
b. equal to one minus the sum of the homozygous genotypes.
c. equal to two times the frequencies of the homozygous genotypes.
d. greater than either homozygous genotype.
e. equal to the frequency of the homozygous dominant genotype minus the frequency of
the homozygous recessive genotype.
Answer: b
30. Cheetahs are a very homogeneous species. The lack of genetic variability among
cheetahs may be attributed to
a. gene flow.
b. sexual selection.
c. population bottleneck.
d. high mutation rate.
e. high immigration rates.
Answer: c
31. Genetic equilibrium in a population refers to
a. equal numbers of dominant and recessive alleles.
b. equal numbers of females and males.
c. unchanging allele frequencies in successive
e. proportional numbers of each genotype.
Answer: c
32. Genetic drift as an evolutionary factor is
a. greater in a population with small numbers than in a population with large numbers.
b. greater in a population with much genetic variation than in a population with little
genetic variation.
c. responsible for the selection of mutations.
d. connected to the movements of alleles between populations of a single species.
e. proportional to the size of a population: the larger the population, the greater the force.
Answer: a
33. In the Hardy–Weinberg equation, the homozygous dominant individuals in a
population are represented by
a. p2.
b. 2pq.
c. q2.
d. p.
e. q.
Answer: a
34–37. The two graphs below represent phenotypic distribution of a character in a
population of organisms over time. The first curve represents the distribution at an initial
sampling time, while the second represents a sampling of a later generation.
34. The average size of an individual at the initial sampling is _______ units.
a. 5
b. 10
c. 15
d. 20
e. 25
Answer: d
35. At the initial sampling, there are as many individuals 15 units tall as there are
individuals _______ units tall.
a. 5
b. 10
c. 15
d. 20
e. 25
Answer: e
36. The process illustrated by these graphs is called
a. stabilizing selection.
b. directional selection.
c. disruptive selection.
d. convergent evolution.
e. divergent evolution.
Answer: b
37. The graphs suggest that
a. taller individuals migrated away from the original population.
b. shorter individuals migrated into the original
c. taller individuals were more successful at reproducing than short individuals were.
e. the individuals in the population continued to grow between sample times.
Answer: c
38. A mutation occurs in one of your lung cells. Which of the following is true?
a. You have evolved to be better adapted to your environment.
b. You will soon die because most mutations are lethal.
c. You will be sterile and no longer be able to have children.
d. The human species will have evolved because this mutation will be passed on to your
children.
e. This mutation does not affect human evolution because it will not be passed on to your
offspring.
Answer: e
39. Natural selection acts directly on the
a. genotype to produce new mutations.
b. phenotype to produce new mutations.
c. genotype to favor existing mutations.
d. phenotype to favor traits due to existing mutations.
e. genotype to inhibit new mutations.
Answer: d
40–43. Biologists use the term “fitness” when speaking of evolution. Below are
descriptions of four male cats. Answer the following questions based on this
Name
Tabby
Chessy
Tony
Tiger
Size
12 lbs
10 lbs
6 lbs
8 lbs
Number of
kittens fathered
19
25
20
20
Kittens surviving
to adulthood
15
14
14
19
Age at death
13 yrs
16 yrs
12 yrs
9 yrs
Comments: Tabby is the largest and strongest cat. Chessy has mated with the most
females. Tony was lost on a family vacation but adapted to street life and lived two more
years. Tiger died from an infection after a cat fight.
40. Which cat contributed the most genes to the next generation?
a. Tabby
b. Chessy
c. Tony
d. Tiger
e. This cannot be answered without more information.
Answer: b
41. Which cat contributed the most genes to the gene pool?
a. Tabby
b. Chessy
c. Tony
d. Tiger
e. This cannot be answered without more information.
Answer: d
42. Which cat contributed the most to the ongoing evolution of the species?
a. Tabby
b. Chessy
c. Tony
d. Tiger
e. This cannot be answered without more information.
Answer: d
43. Which cat is the “fittest”?
a. Tabby
b. Chessy
c. Tony
d. Tiger
e. This cannot be answered without more information.
Answer: d
44–46. In a population of 200 individuals, 72 are homozygous recessive for the character
of eye color (cc). One hundred individuals from this population die due to a fatal disease.
Thirty-six of the survivors are homozygous recessive. Answer the following questions.
44. In the original population, the frequency of the dominant allele is
a. 0.16.
b. 0.36.
c. 0.40.
d. 0.48.
e. 0.60.
Answer: c
45. In the new population, the frequency of the dominant allele is
a. 0.16.
b. 0.36.
c. 0.40.
d. 0.48.
e. 0.60.
Answer: c
46. How many heterozygous individuals are expected in the new population?
a. 16
b. 36
c. 40
d. 48
e. 60
Answer: d
47. Which of the following is not an effect of sexual recombination on alleles?
a. Greater evolutionary potential
b. Change in the frequency of specific alleles
c. Greater genotypic variety
d. New combinations of genetic material
e. Greater phenotypic variety
Answer: b
48. An allele that does not affect the fitness of an organism is called a _______ allele.
a. neutral
b. directional
c. distributed
d. positive
e. natural
Answer: a
STUDY GUIDE QUESTIONS
Knowledge and Synthesis Questions
1. Evolution occurs at the level of
a. the individual genotype.
b. the individual phenotype.
c. environmentally based phenotypic variation.
d. the population.
2. What does natural selection act on?
a. The gene pool of the species
b. The genotype
c. The phenotype
d. Multiple gene inheritance systems
3. Which choice would form a statement about Mendelian populations that is not true? A
Mendelian population must
a. consist of members of the same species.
b. have members that are capable of interbreeding.
c. show genetic variation.
d. have a gene pool.
4. In comparing several populations of the same species, the population with the greatest
genetic variation would have the
a. greatest number of genes.
b. greatest number of alleles per gene.
c. greatest number of population members.
d. largest gene pool.
5. The ability to taste the chemical PTC (phenylthiocarbamide) is determined in humans
by a dominant allele T, with tasters having the genotypes Tt or TT and nontasters having
tt. If you discover that 36 percent of the members of a population cannot taste PTC, then
according to the Hardy–Weinberg rule, the frequency of the T allele should be
a. 0.4.
b. 0.6.
c. 0.64.
d. 0.8.
6. A gene in humans has two alleles, M and N, that code for different surface proteins on
red blood cells. If you know that the frequency of allele M is 0.2, according to the Hardy–
Weinberg rule, the frequency of the genotype MN in the population should be
a. 0.16.
b. 0.32.
c. 0.64.
d. 0.8.
7. If the frequency of allele b in a gene pool is 0.2, and the population is in Hardy–
Weinberg equilibrium, the expected frequency of the genotype bbbb in a tetraploid (4n)
plant species would be
a. 0.0016.
b. 0.04.
c. 0.08.
d. 0.2.
8. Random genetic drift would probably have its greatest effect on which of the following
populations?
a. A small, isolated population.
b. A large population in which mating is nonrandom.
c. A large population in which mating is random.
d. A large population with regular immigration from a neighboring population.
9. Allele frequencies for a gene locus are least likely to be significantly changed by
a. nonrandom mating.
b. the founder effect.
c. mutation.
d. gene flow.
10. Select all of the following evolutionary agents that produce nonrandom changes in the
genetic structure of a population.
a. Self-fertilization
b. Population bottlenecks
c. Mutation
d. Natural selection
11. Suppose a particular species of flowering plant that lives only one year can produce
red, white, or pink blossoms, depending on its genotype. Biologists studying a population
of this species count 300 red-flowering, 500 white-flowering, and 800 pink-flowering
plants in a population. When the population is censused the following year, 600 redflowering, 900 white-flowering, and 1,000 pink-flowering plants are observed. Which
color has the highest fitness?
a. Red
b. White
c. Pink
12. The following graph shows the range of variation among population members for a
trait determined by multiple genes.
If this population is subject to stabilizing selection for several generations, which of the
distributions (a–d) is most likely to result?
13. In areas of Africa in which malaria is prevalent, many human populations exist in
which the allele that produces sickle-cell disease and the allele for normal red blood cells
occur at constant frequencies, despite the fact that sickle-cell disease frequently causes
death at an early age. This is an example of
a. the founder effect.
b. a stable polymorphism.
c. mutation.
d. nonrandom mating.
Answers
Knowledge and Synthesis Answers
1. d. Evolution is defined as changes in the genetic structure of a population over time, so
evolution occurs at the level of the population.
2. c. Natural selection acts on phenotypes, not genotypes. For example, a harmful
recessive allele is “invisible” to natural selection when it occurs in a heterozygote, where
its harmful effect is masked by the dominant allele.
3. c. Although most populations show genetic variation, this condition is not part of the
definition of a Mendelian population.
4. b. Genetic variation is related to the number of different alleles per gene. Regarding
choice a, recall that all species members have the same number of genes. Population size
per se has little to do with genetic variation, so choices c and d are also incorrect.
5. a. Recall that q2 = 0.36 is the frequency of the tt genotype, so q (0.6, the square root of
0.36) is the frequency of thet allele. Assuming there are only two alleles for this trait, T +
t = 1. The frequency of the T allele is therefore 1 – t = 1 – 0.6 = 0.4.
6. b. Because p = 0.2 and therefore, q = 1 – 0.2 = 0.8, the frequency of the MN genotype
is 2pq, or 2 × 0.2 × 0.8 = 0.32.
7. a. The probability of one allele b in a genotype is equal to its frequency, or 0.2, so the
probability that all four of the alleles in a tetraploid organism will be b would be (0.2)4, or
0.0016.
8. c. Genetic drift is most significant in small populations.
9. a. Unlike the founder effect, mutation and gene flow, all of which change allele
frequencies in a population, nonrandom mating only causes a deviation from the
frequency of heterozygotes predicted by Hardy–Weinberg equilibrium.
10. a and d. Self-fertilization leads to increased numbers of homozygous individuals, and
natural selection is also nonrandom.
11. a. Fitness measures the relative contribution of a genotype or phenotype to
subsequent generations. The red-flowering plants, which doubled in number, had the
greatest percentage increase of any of the plants and thus had the highest fitness.
12. a. Stabilizing selection results when individuals that are intermediate in phenotype
make a larger contribution to future generations than individuals of more extreme
phenotype. This leads to reduced variation for the trait and causes the curve to be higher
and narrower. Curve b shows greater variation, curve c would result from disruptive
selection, and curve d from directional selection.
13. b. Polymorphism in a population is the existence of two or more alleles at a particular
gene locus at frequencies greater than mutations can produce. If phenotypes are stable
through time, then the underlying alleles will also be constant. In this instance, the
polymorphism is stable because malaria is a significant cause of mortality in some parts
of Africa, and heterozygotes have greater resistance to this disease than individuals with a
“normal” phenotype. Thus the superior fitness of the heterozygotes maintains both alleles
in the population.
TEXTBOOK SELF QUIZ QUESTIONS
1. The two major components of Darwin’s theory of evolution are that
a. evolution is a fact, and mutations are the agent of evolution.
b. evolution is a fact, and natural selection is the agent of evolution.
c. species cannot change into other species, but natural selection can modify them.
d. species cannot change into other species, but mutations can modify them.
e. evolution is a hypothesis, and genetic drift is the agent of evolution.
2. To ground his theory, Charles Darwin
a. developed a comprehensive theory of inheritance.
b. described several evolutionary changes and identified the agents that caused them.
c. used patterns of domestication to show how his theory differed from those patterns.
d. assembled a broad base of supporting information from many fields.
e. developed a mathematical model of evolutionary change.
3. The phenotype of an organism is
a. the type specimen of its species in a museum.
b. its genetic constitution, which governs its traits.
c. the chronological expression of its genes.
d. the physical expression of its genotype.
e. the form it achieves as an adult.
4. The appropriate unit for defining and measuring genetic variation is the
a. cell.
b. individual.
c. population.
d. community.
e. ecosystem.
5. Which statement about allele frequencies is not true?
a. The sum of any set of allele frequencies is always 1.
b. If there are two alleles at a locus and we know the frequency of one of them, we can
obtain the frequency of the other by subtraction.
c. If an allele is missing from a population, its frequency is 0.
d. If two populations have the same gene pool for a locus, they will have the same
proportion of homozygotes at that locus.
e. If there is only one allele at a locus, its frequency is 1.
6. In a population at Hardy–Weinberg equilibrium in which the frequency of A alleles (p)
is 0.3, the expected frequency of Aa individuals is
a. 0.21.
b. 0.42.
c. 0.63.
d. 0.18.
e. 0.36.
7. Natural selection that preserves existing allele frequencies is called
a. unidirectional selection.
b. bidirectional selection.
c. prevalent selection.
d. stabilizing selection.
e. preserving selection.
8. The fitness of a genotype is determined by the
a. average rates of survival and reproduction of individuals with that genotype.
b. individuals that have the highest rates of both survival and reproduction.
c. individuals that have the highest rates of survival.
d. individuals that have the highest rates of reproduction.
e. average reproductive rate of individuals with that genotype.
9. Laboratory selection experiments with fruit flies have demonstrated that
a. bristle number is not genetically controlled.
b. bristle number is not genetically controlled, but changes in bristle number are caused
by the environment in which the fly is raised.
c. bristle number is genetically controlled, but there is little variation on which natural
selection can act.
d. bristle number is genetically controlled, but selection cannot result in flies having more
bristles than any individual in the original population had.
e. bristle number is genetically controlled, and selection can result in flies having more
bristles than any individual in the original population had.
10. Disruptive selection maintains a bimodal distribution of bill size in the West African
seedcracker because
a. bills of intermediate shapes are difficult to form.
b. the two major food sources of the finches differ markedly in size and hardness.
c. males use their large bills in displays.
d. migrants introduce different bill sizes into the population each year.
e. older birds need larger bills than younger birds.
11. A population is said to be polymorphic for a locus if it has at least
a. three different alleles at that locus.
b. two different alleles at that locus.
c. two genotypes for that locus.
d. three genotypes for that locus.
e. two alleles for that locus, the rarest of which is more common than expected by
mutation alone.
Answers
1. b
2. d
3. d
4. c
5. d
6. e
7. d
8. b
9. e
10. b
11. c
ONLINE QUIZ QUESTIONS
1.Darwin observed that although offspring can resemble their parents, the offspring are
not identical to each other or their parents. This is an example of
a. artificial selection.
b. the origin of species.
c. adaptation.
d. population genetics.
e. natural selection.
Answer: e
2.Which of the following is not a cause of changes in the genetic structure of population?
a. Mutation
b. Gene flow
c. Genetic drift
d. Random mating
e. Natural selection
Answer: d
3.The genotype of an organism is
a. the type specimen of its species in a museum.
b. its genetic constitution, which governs its traits.
c. a characteristic of an organism that is partly determined by its genes.
d. the physical expression of its genotype.
e. the form it achieves as an adult.
Answer: b
4.The origin of genetic variation is
a. mutation.
b. gene flow.
c. genetic drift.
d. nonrandom mating.
e. natural selection.
Answer: a
5.Which of these conditions is not necessary for Hardy-Weinberg equilibrium?
a. Random mutation
b. Very large population size
c. Unlimited migration between populations
d. There is no mutation.
e. Natural selection does not affect the alleles under consideration.
Answer: c
6.In a population at Hardy-Weinberg equilibrium in which the frequency of A alleles (p)
is 0.1, the expected frequency of Aa individuals is
a. 0.21.
b. 0.42.
c. 0.63.
d. 0.18.
e. 0.36.
Answer: d
7.The random loss of alleles is known as
a. mutation.
b. gene flow.
c. genetic drift.
d. nonrandom mating.
e. natural selection.
Answer: c
8.Which of these is the only agent of evolution that adapts populations to their
environments?
a. Mutation
b. Gene flow
c. Genetic drift
d. Nonrandom mating
e. Natural selection
Answer: e
9.Natural selection may be constrained in its action because
a. the necessary genetic variation may be lacking.
b. evolutionary theory does not allow a population to temporarily get worse.
c. major evolutionary innovations are rare.
d. insufficient phenotypic plasticity may be present.
e. All of the above
Answer: e
10.Adaptation is studied by
a. altering the form of an organism and observing the consequences.
b. testing predictions by comparing traits in many species.
c. developing theoretical models.
d. selecting for traits in the laboratory.
e. All of the above
Answer: e
11.A population is said to be polymorphic for a locus if it has at least
a. three different alleles at that locus.
b. two different alleles at that locus.
c. two genotypes for that locus.
d. three genotypes for that locus.
e. two genotypes for that locus, the rarest of which is more common than expected by
mutation alone.
Answer: e
12.Natural selection may be constrained in its action because
a. the necessary genetic variation may be lacking.
b. evolutionary theory does not allow a population to temporarily get worse.
c. major evolutionary innovations are rare.
d. insufficient phenotypic plasticity may be present.
e. All of the above
Answer: e
13.Adaptation is studied by
a. altering the form of an organism and observing the consequences.
b. testing predictions by comparing traits in many species.
c. developing theoretical models.
d. selecting for traits in the laboratory.
e. All of the above
Answer: e
14.What kind of selection is present if both the smallest and the largest individuals
contribute relatively fewer offspring to the next generation than those closer to the
center?
a. Disruptive selection
b. Stabilizing selection
c. Disruptive selection and stabilizing selection
d. Directional selection
e. Directional selection and stabilizing selection
Answer: b
15.What kind of selection leads to increases in the proportion of a population exhibiting
phenotypes at one extreme of the spectrum?
a. Disruptive selection
b. Stabilizing selection
c. Disruptive selection and stabilizing selection
d. Directional selection
e. Directional selection and stabilizing selection
Answer: d
16.What kind of selection leads to increases in the proportion of a population exhibiting
phenotypes at both extremes of the spectrum?
a. Disruptive selection
b. Stabilizing selection
c. Disruptive selection and stabilizing selection
d. Directional selection
e. Directional selection and stabilizing selection
Answer: a