Midterm 2 A+

Question 1

{Plato’s concept of the scala naturae}
(a) proposed that the world is composed of a limited number of unchanging essences that are
(b). established a view of the natural world that arranged organisms in a linear sequence
discretely different from one another
( c) paved the way for Darwin’s theory of evolution by providing a clear mechanism that could drive
adaptive evolution: organisms striving for perfection
(d) laid the groundwork for a view of living organisms as being distributed along with the tips of a
branching tree
(e) explained how fossils documented a sequence of increasingly complex, ‘advanced’ organisms in
shallower sedimentary rock deposits

Answer 1

b. established a view of the natural world that arranged organisms in a linear sequence

Question 2

{If gene A (with alleles A1 and A2) and gene B (with alleles B1 and B2) are found close together on the
the same chromosome}
a. they will still obey Mendel’s Second Law, the law of independent assortment
b. then the mating A1A1B1B1 x A2A2B2B2 will produce a double heterozygote (A1A2B1B2) that will
produce only two types of gametes: A1B1 and A2B2
c. then the mating A1A1B1B1 x A2A2B2B2 will produce a double heterozygote (A1A2B1B2) that will
produce only two types of gametes: A1B2 and A2B1
d. then the mating A1A1B1B1 x A2A2B2B2 will produce a double heterozygote (A1A2B1B2) that will
produce four types of gametes, each equally common: A1B1, A2B2, A1B2, and A2B1.
e. then the mating A1A1B1B1 x A2A2B2B2 will produce a double heterozygote (A1A2B1B2) that will
produce four types of gametes, two of which, A1B1 and A2B2, will be more common, and two of
which, A1B2, and A2B1, will be less common.

Answer 2

e. then the mating A1A1B1B1 x A2A2B2B2 will produce a double heterozygote (A1A2B1B2) that will
produce four types of gametes, two of which, A1B1 and A2B2, will be more common, and two of
which, A1B2, and A2B1, will be less common.

Question 3

(Mendel’s demonstration that inheritance operates through a particulate mechanism: )
a. was important, because it shows that natural selection can operate as a powerful process of
adaptive evolution
b. explains why, with co-dominant alleles, heterozygotes exhibit a phenotype that is intermediate
between the two homozygotes
c. means that key adaptive mutations are progressively ‘blended away’ each generation, as matings
mix the adaptive mutation with the alleles that dominated the population before the mutation
appeared
d. allows diploid, sexual populations with heterozygote advantage and random mating to produce
100% heterozygous offspring
e. explained why an individual’s genotype can always be reliably predicted from its phenotype

Answer 3

a. was important, because it shows that natural selection can operate as a powerful process of
adaptive evolution

Question 4

(genetic drift )
a. is a second major mechanism by which evolution produces adaptations
b. is an important mechanism for generating and maintaining genetic variation within populations
c. is a major cause of allele frequency changes that dominates evolutionary processes any time we
have 1/N &laquo_space;s, when N is population size and s is the selection coefficient
d. only operates on strictly neutral traits
e. is a major destroyer of genetic variation within populations

Answer 4

e. is a major destroyer of genetic variation within populations

Question 5

[A single, clonally-reproducing female snail that produces offspring genetically identical to herself is
allowed to reproduce in nature until she has produced 1000 offspring. If you measure body weight at
maturity among the 1000 offspring then you will likely find:]
a. almost zero variation in body weight, because there is zero genetic variation in the population;
there will also be no response to directional selection
b. a continuous array of trait values, with the distribution of trait values that is approximately bell-
shaped; this population will respond to strong, consistent directional selection for larger weight by
evolving increased body size
c. a continuous array of trait values, with the distribution of trait values that is approximately bell-
shaped; nevertheless, this population will NOT respond to many generations of directional
selection for larger weight
d. snails that exhibit substantial variation in body size, because genetic drift operating on the
the population will create changes in allele frequencies at genes influencing body size
e. snails that vary a lot in body size, because natural selection will favor extreme body size
phenotypes as a way of reducing intraspecific competition

Answer 5

c. a continuous array of trait values, with the distribution of trait values that is approximately bell-
shaped; nevertheless, this population will NOT respond to many generations of directional
selection for larger weight

Question 6

[ Insecticide resistance alleles: ]
a. are often expressed as dominant traits when the biochemical mechanism involves target-site
insensitivity
b. are often expressed as co-dominant traits when the biochemical mechanism involves target-site
insensitivity
c. are often expressed as recessive traits when the biochemical mechanism involves target-site
insensitivity
d. are often expressed as co-dominant traits when the biochemical mechanism involves detoxication
e. are often expressed as recessive traits when the biochemical mechanism involves detoxication

Answer 6

c. are often expressed as recessive traits when the biochemical mechanism involves target-site
insensitivity

Question 7

[The core idea behind the high-dose, refuge strategy for managing resistance in insect pests to transgenic crop plants expressing Bacillus thuringiensis-derived protein toxins is that resistance evolution can be blocked because:]
a. the high dose kills all genotypes, including SS, RS, and RR, thereby preventing natural selection
from discriminating between different genotypes
b. persistent immigration of SS individuals from a refuge causes a dilution of the R allele frequency,
thereby preventing resistance allele frequencies from increasing
c. the R gene can be made to function as a functionally dominant trait
d. the RS heterozygotes formed as the offspring of SS x RR matings are themselves susceptible to
the high dose, allowing R alleles to be removed from the population
e. by keeping the population small through the use of a high toxin dose, we can make genetic drift
more powerful than natural selection, and thereby prevent adaptive evolution from occurring

Answer 7

d. the RS heterozygotes formed as the offspring of SS x RR matings are themselves susceptible to
the high dose, allowing R alleles to be removed from the population

Question 8

[ Predators can suppress local populations of prey ]
a. by attacking and killing prey individuals
b. by causing prey individuals to express costly anti-predator defenses, which may in turn be
associated with a loss of prey reproduction
c. enhancing emigration, as prey choose to leave habitat patches that they judge to be high-risk
locations
d. suppressing immigration, as prey make choices to avoid entering habitat patches that they judge
to be dangerous
e. a – d above are all true

Answer 8

e. a – d above are all true

Question 9

The Lotka-Volterra model of predator (P) interactions with prey (N) populations is as follows:

a. predator mortality rate
b. predator attack rate on prey
c. the efficiency with which predators convert consumed prey into new predator offspring
d. the carrying capacity of the predator population
e. the equilibrium density of predators in the habitat

Answer 9

c. the efficiency with which predators convert consumed prey into new predator offspring

Question 10

[Our textbook explains that Darwin got many of his key ideas about genetic variation and selection by]
a. studying fossils that demonstrated conclusively the gradual transition of animals from one form to
another
b. observing the effects of artificial selection on crop plants and domesticated animals like pigeons
c. recognizing that natural selection would be very powerful under a particulate inheritance
mechanism
d. studying mutational processes in finches (birds) found on oceanic islands, like the Galapagos
e. distinguishing between the effects of goal-oriented processes, like selection, versus random
processes like genetic drift

Answer 10

b. observing the effects of artificial selection on crop plants and domesticated animals like pigeons

Question 11

Does intra-specific (i.e., within-species) competition generally create density-
dependence in the demographic rates (b, d, i, and e) of populations? What kind of
feedback, if any, would you expect to be generated on population growth? Explain your
answer briefly. (6 points)

Answer 11

: Yes. Intraspecific competition generally produces density-dependent birth rates
(often decreasing as density increases), death rates (often increases as density
increases), and sometimes also emigration (increasing in response to intensifying
competition in high-density populations) and immigration (decreasing in response to
intensifying competition in high-density populations). These are all negative
feedbacks, acting to inhibit further population growth once high populations are
reached.

Question 12

Does cannibalism generally create density-dependence in the demographic rates (b, d, i,
and e) of populations? What kind of feedback, if any, would you expect to be generated
on population growth? Explain your answer briefly. (6 points)

Answer 12

Yes. Cannibalism operates quite similarly to intraspecific competition.
Cannibalism mostly increases death rates as population density increases. It’s
possible that emigration might increase, and immigration decrease. These effects on
d, e, and i are all negative feedbacks, acting to inhibit further population growth
once high populations are reached. (NOTE: cannibalism could elevate birth rates in
surviving cannibals, if the meal increases their reproductive output. This would be a
positive feedback, causing further increases in population growth. We don’t expect
this effect to fully offset the more important increases in death rates in the
cannibalistic population.)

Question 13

Does inter-specific (i.e., between-population) competition generally create density-
dependence in the demographic rates (b, d, i, and e) of populations? What kind of
feedback, if any, would you expect to be generated on population growth? Explain your
answer briefly. (8 points)

Answer 13

Answer:
Yes, Interspecific competition generates density dependent demographic rates and
positive feedback on population growth of a focal population. If our focal species
(Species A) is present at high density, this will tend to depress densities of its
interspecific competitor (Species B). Lower densities of Species B relaxes interspecific
competition felt by Species A, allowing the density of Species A to get still higher.
This is positive feedback. This is why interspecific competition will (often) lead to
competitive exclusion and local extinction of one of the competing species.

Question 14

1 Most caterpillars are herbivorous, feeding strictly on plant material. However, in one group
of moths, the caterpillar stage has evolved to become predatory, eating other herbivorous
insects. Using the three conditions that are necessary and sufficient for evolution by natural
selection, explain how a predatory caterpillar might have evolved from an herbivorous
caterpillar. (12 points)

Answer 14

Answer:
(1) Variation in the phenotype: some caterpillars must have been more willing to
consume prey (in this case, other herbivores) than others, which were strictly
herbivorous and rejected opportunities to consume prey.
(2) Inheritance: the offspring of the more predatory caterpillars must have inherited the
propensity to feed as a predator.
(3) Differential mean expectation of reproductive success (or, differential fitness): the
caterpillars that were more predatory must have had a higher reproductive success
(for whatever reason: perhaps insect prey are higher-quality food than plant material,
because insect prey have higher nutrient content or lower levels of chemical defense
against predators).

Question 15

14. You are studying evolution in a plant population that has one generation per year. The
    population has two alleles at one locus, B1 and B2, that are equally common: frequency(B1)
    = frequency(B2) = 0.5. Although the two alleles do influence the phenotype (B1 causes one
    hair to grow on each leaf tip, and B2 causes two hairs to grow on each leaf tip), they are
    associated with no difference in mean expectation of reproductive success (that is, they are
    strictly neutral). You visit a small population of this plant (100 total individuals; population
    size is stable over time) that inhabits a tiny island, where the population is isolated from
    immigration. If you track the frequency of the two alleles over a long period of time (say,
    1,000 years), do you expect the frequency of the B1 allele to go up, to go down, or to stay
    the same? Explain your answer briefly. (10 points)

Answer 15

Answer: The frequency of the B1 allele is likely to change under the influence of genetic
drift, which is likely to be strong because the population is small. It is just as likely to
go up (approximately 50% chance) as it is to go down (approximately 50% chance).
It is very, very unlikely that it would stay exactly the same.

Question 16

Does cannibalism generally create density-dependence in the demographic rates (b, d, i,
and e) of populations? What kind of feedback, if any, would you expect to be generated
on population growth? Explain your answer briefly. (6 points)

Answer 16

Answer: Yes. Cannibalism operates quite similarly to intraspecific competition.
Cannibalism mostly increases death rates as population density increases. It’s
possible that emigration might increase, and immigration decrease. These effects on
d, e, and i are all negative feedbacks, acting to inhibit further population growth
once high populations are reached. (NOTE: cannibalism could elevate birth rates in
surviving cannibals, if the meal increases their reproductive output. This would be a
positive feedback, causing further increases in population growth. We don’t expect
this effect to fully offset the more important increases in death rates in the
cannibalistic population.)

Question 17

1. Which of the following is NOT one of the assumptions underlying the Hardy-Weinberg
   equilibrium:
   a. no selection
   b. very large population size
   c. co-dominant alleles
   d. no mutation
   e. random mating

Answer 17

c. co-dominant alleles

Question 18

2. Scientific advances in geology helped to lay the groundwork for establishing a theory of
   evolution by showing that:
   a. the formation of sedimentary rock and erosion are slow processes that must have been
   operating over vast periods of time on earth
   b. volcanic activity was likely to have caused climate change
   c. oxygen availability was essential for photosynthesis in the ancient seas of earth
   d. soils contain key nutrients that plants use for growth and reproduction
   e. a-d above are all true

Answer 18

a. the formation of sedimentary rock and erosion are slow processes that must have been
operating over vast periods of time on earth

Question 19

3. Mendel’s first law, the law of segregation, says
   a. the process of development, during which genes influence the phenotype, operates in a
   strictly particulate manner; offspring phenotypes are therefore rarely found to be
   intermediate between the phenotypes of their parents
   b. the process of development, during which genes influence the phenotype, operates in a
   strictly blending manner; offspring phenotypes are therefore universally found to be
   intermediate between the phenotypes of their parents
   c. the process of inheritance, through which genes are passed down from one generation to
   the next, is strictly particulate
   d. the process of inheritance, through which genes are passed down from one generation to
   the next, is strictly blending
   e. genes found close together on the same chromosome segregate independently during
   the formation of gametes

Answer 19

c. the process of inheritance, through which genes are passed down from one generation to
the next, is strictly particulate v

Question 20

The high dose, refuge strategy for preventing insect pests from evolving resistance to Bt-
transgenic crop plants
a. relies on a dose of the Bt toxin that is high enough to kill insects with genotype RS
b. relies on a source of abundant SS immigrants that move into the transgenic crop field
c. relies on the rare RR individuals, which will survive the high dose, subsequently mating
with SS immigrants, producing RS offspring
d. is more likely to be effective when resistance traits are based on target-site insensitivity,
making the R allele likely to be recessive
e. a-d above are all true

Answer 20

e. a-d above are all true

Question 21

In the Lotka-Volterra model of interspecific competition, if species 1 is a small, seed-eating beetle and species 2 is a large bird that eats exactly the same seeds as the beetle eats, then:
if species 1 is a small, seed-eating beetle and species 2 is a large bird that eats exactly the
same seeds as the beetle eats, then:
a. a12 = a21 = 0.0
b. a12 = a21 = 1.0
c. a12 &laquo_space;1.0 and a21&raquo_space; 1.0
d. a12&raquo_space; 1.0 and a21 &laquo_space;1.0
e. the larger bird is predicted to competitively displace the smaller beetle

Answer 21

d. a12&raquo_space; 1.0 and a21 &laquo_space;1.0

Question 22

In competitive character displacement exhibited by two species of spadefoot toads
a. the two species diverge in their use of resources in ponds where they are present
together
b. the two species use similar resources in ponds where they are present together, and
more different resources where they are present in ponds alone
c. stabilizing selection acts on each species when they are present in ponds alone
d. disruptive selection acts on each species when both species are present in the same
pond
e. directional selection acts on each species when they are present in ponds alone

Answer 22

a. the two species diverge in their use of resources in ponds where they are present
together

Question 23

Predators:
a. have their full impact on prey population growth rate by elevating the prey’s per capita
death rate, d
b. can reduce the per capita birth rate of the prey population, b, by causing the prey to
express costly anti-predator behaviors
c. frequently suppress the per capita emigration rate, e, from high-risk prey populations
d. rarely have any influence, either positive or negative, on the prey population per capita
immigration rate, i
e. a – d above are all true

Answer 23

b. can reduce the per capita birth rate of the prey population, b, by causing the prey to
express costly anti-predator behaviors

Question 24

Vaccination programs implemented in human populations
a. can reduce the risk of infection of the vaccinated individuals
b. can reduce the risk of infection of the unvaccinated individuals
c. must vaccinate a high proportion of the population, >90%, in order to prevent an
epidemic for highly contagious diseases, when the reproductive number, R0, is very high,
>10
d. must vaccinate only a modest proportion of the population, >50%, in order to prevent an
epidemic for a moderately contagious disease, for which the reproductive number R0 =
2.0
e. a – d above are all true

Answer 24

e. a – d above are all true

Question 25

Vaccination programs implemented in human populations
a. can reduce the risk of infection of the vaccinated individuals
b. can reduce the risk of infection of the unvaccinated individuals
c. must vaccinate a high proportion of the population, >90%, in order to prevent an
epidemic for highly contagious diseases, when the reproductive number, R0, is very high,
>10
d. must vaccinate only a modest proportion of the population, >50%, in order to prevent an
epidemic for a moderately contagious disease, for which the reproductive number R0 =
2.0
e. a – d above are all true

Answer 25

e. a – d above are all true

Question 26

9. The Lotka-Volterra model of predator (P) interactions with prey (N) populations is as follows:
   a. the intrinsic rate of increase of the prey population
   b. the predator attack rate on prey
   c. the efficiency with which predators convert consumed prey into new predator offspring
   d. the carrying capacity of the predator population
   e. the per capita death rate of the predator population

Answer 26

b. the predator attack rate on prey

Question 27

Our textbook explains that
a. most parasites have broad host ranges, such that there are more species of hosts than
parasites across the tree of life
b. competition between multiple parasites on the same host species means that most host
species can be attacked by at most a single, highly specialized parasite species
(competitive exclusion)
c. most hosts harbor multiple parasite species, many of which are relatively host-
specialized; roughly 50 percent of the species on Earth are parasites
d. parasites do not adversely affect the health of their host, since they rely on their host for
their own reproduction
e. parasites generally evolve to have elevated virulence, such that parasites eventually
impose high mortality on their co-evolved hosts

Answer 27

c. most hosts harbor multiple parasite species, many of which are relatively host-
specialized; roughly 50 percent of the species on Earth are parasites

Question 28

(C) Explain briefly why natural selection can achieve a much lower equilibrium frequency of
a deleterious allele when the allele is dominant than when the allele is recessive. (8
points)

Answer 28

Answer: Natural selection acts very effectively against a dominant allele, regardless of
whether the allele is common or rare, because the allele is always expressed,
regardless of whether it is present in a heterozygous state (A1A2) or a homozygous
state (A2A2). It is never shielded, or hidden, from selection. In contrast, a recessive
deleterious allele is only expressed when it is present in a homozygous state (A2A2).
Homozygotes are rare when the frequency of the allele is small, and instead most of
the alleles are present in a heterozygote state (A1A2), which shields the A2 from the
effects of selection. Thus, selection against a deleterious allele becomes very weak
as the frequency of the allele drops. Mutation can generate new copies of the
deleterious allele as quickly as selection can remove them from the population.

Question 29

12. Most caterpillars are herbivorous, feeding strictly on plant material. However, in one group
    of moths, the caterpillar stage has evolved to become predatory, eating other herbivorous
    insects. Using the three conditions that are necessary and sufficient for evolution by natural
    selection, explain how a predatory caterpillar might have evolved from an herbivorous
    caterpillar. (12 points)

Answer 29

Answer:
(1) Variation in the phenotype: some caterpillars must have been more willing to
consume prey (in this case, other herbivores) than others, which were strictly
herbivorous and rejected opportunities to consume prey.
(2) Inheritance: the offspring of the more predatory caterpillars must have inherited the
propensity to feed as a predator.
(3) Differential mean expectation of reproductive success (or, differential fitness): the
caterpillars that were more predatory must have had a higher reproductive success
(for whatever reason: perhaps insect prey are higher-quality food than plant material,
because insect prey have higher nutrient content or lower levels of chemical defense
against predators).

Question 30

. What do you expect to happen to the frequency of the B1B2 heterozygotes in the small,
isolated plant population described in question (14) over the same 1000 generation period?
Explain your answer briefly. (6 points)

Answer 30

Answer: The frequency of the B1B2 heterozygote will almost certainly drop. When the
two alleles are equally common, the frequency(B1B2) = 2(freq(B1))(freq(B2)) =
2(0.5)(0.5) = 0.5, which is the highest heterozygote frequency that can be achieved.
Any change in the frequency of the two alleles will cause this frequency to drop. In
fact, over a large number of generations, it is actually likely that one of the two alleles
(B1 or B2) will be lost, as the allele frequency drifts to zero. In this case, the final
heterozygote frequency will be zero. This is a demonstration of the general result
that genetic drift tends to remove genetic variation from populations.

Question 31

. In a world where inheritance operated through a blending mechanism
a. natural selection would be a substantially weakened mechanism of evolution
b. new mutations that conferred major fitness advantages would be ‘blended away’ across
generations, and largely lost before they could generate major adaptive evolution
c. all members of populations would converge on the same genotype over time
d. mutation could still occur
e. a – d above are all true

Answer 31

e. a – d above are all true

Question 32

2. For traits like height in a human population, it is hard to look at an individual’s phenotype and infer
   their genotype because:
   a. height is a trait that is influenced by many genes
   b. height is influenced by the environment in which an individual grows up
   c. genes that influence an individual’s height are shaped by natural selection, but not by genetic drift
   d. a and b are both true v

Answer 32

d. a and b are both true

Question 33

3. Insecticide resistance is less likely to evolve in populations of predatory insects, compared to
   herbivorous insects, because
   a. predatory insects have more highly developed detoxification enzymes than do herbivorous insects
   b. herbivorous insects may receive lower doses of insecticide toxins as they ingest plant material
   bearing insecticide residues
   c. predators that survive an insecticide application may still have low fitness, because they may have
   no prey to eat
   d. the high dose refuge strategy will slow resistance evolution in predatory species but not in
   herbivorous insects
   e. resistance is more likely to be functionally dominant in predator than in herbivore populations

Answer 33

c. predators that survive an insecticide application may still have low fitness, because they may have
no prey to eat

Question 34

Predators

a. often decrease prey population per capita birth rates by causing prey to express costly defensive behaviors
b. often increase prey population death rates
c. may increase prey population emigration rates from habitat patches where predation risk is high
d. may decrease prey population immigration rates to habitat patches where predation risk is high
e. a - d above are all true

Answer 34

e. a - d above are all true

Question 35

6. In the Lotka-Volterra model of predator-prey interactions, shown below, the parameter “f” tells us
   a. the number of predator births occurring for each prey consumed
   b. the number of prey encountered per unit time
   c. the likelihood that an encountered prey is actually captured successfully
   d. the predator population per capita death rate
   e. the predator population per capita birth rate

Answer 35

a. the number of predator births occurring for each prey consumed

Question 35

6. In the Lotka-Volterra model of predator-prey interactions, shown below, the parameter “f” tells us
   a. the number of predator births occurring for each prey consumed
   b. the number of prey encountered per unit time
   c. the likelihood that an encountered prey is actually captured successfully
   d. the predator population per capita death rate
   e. the predator population per capita birth rate

Answer 35

a. the number of predator births occurring for each prey consumed

Question 36

7. Masting in California oaks:
   a. produces density-independent mortality for oak seeds (acorns)
   b. produces negative feedback on oak density, a stabilizing influence
   c. produces positive feedback on oak density, a destabilizing influence
   d. involves production of a relatively steady number of acorns each year, even when environmental
   conditions vary
   e. synchronizes peaks in the number of acorns produced with peaks in the number of acorn-
   consuming herbivores present

Answer 36

c. produces positive feedback on oak density, a destabilizing influence

Question 37

Under directional selection in which individuals with higher trait values have higher fitness, we expect
the mean trait value to increase
a. as long as population size is finite
b. as long as mortality and birth processes are not shaped by chance processes
c. as long as variance in trait values due to environmental effects = 0
d. as long as trait heritability > 0
e. a – d above are all true

Answer 37

d. as long as trait heritability > 0

Question 38

Most biologists working in the 1800’s believed that inheritance operated through some sort of blending
process, in part because
a. crosses between two morphologically distinct varieties of plants often produced hybrid offspring
that expressed traits that were intermediate between the traits of the parents
b. offspring expressed traits that were more similar to traits expressed by their mothers than their
fathers
c. offspring expressed traits that were more similar to traits expressed by their fathers than their
mothers
d. it was widely recognized that an organism’s phenotype is shaped in part by its environment
e. opportunities for inheritance of acquired characteristics were thought to be significantly
strengthened by a mode of inheritance based on blending inheritance

Answer 38

a. crosses between two morphologically distinct varieties of plants often produced hybrid offspring that expressed traits that were intermediate between the traits of the parents

Question 39

10. In all the examples we covered in class, patterns of Mendelian inheritance did not depend on which
    parental genotype was carried by the mother and which parental genotype was carried by the father. In the textbook, examples are given that violate this pattern, including:
    a. when two genes are found close together on the same autosome (autosomal linkage)
    b. when genes of interest are found on cytoplasmic organelles (mitochondria or chloroplasts)
    c. when genes of interest are found on sex chromosomes
    d. a and c are both true
    e. b and c are both true

Answer 39

e. b and c are both true

Question 40

Natural selection and genetic drift are two important processes by which evolution occurs.

(A) Is the presence of phenotypic variation a necessary condition for evolution by natural selection? Explain your answer briefly. (3 points)

Answer 40

Answer: YES. Without phenotypic variation, natural selection cannot operate (natural selection operates when different phenotypic variants – individuals that express different traits – have different mean expectations of reproductive success).

Question 41

(B) Is the presence of phenotypic variation a necessary condition for evolution by genetic drift? Explain your answer briefly. (4 points)

Answer 41

Answer: NO. Genetic drift can still operate without phenotypic variation; all that is needed is genetic variation, whether expressed or not. For example, neutral genetic variation
associated with synonymous (or silent) DNA variation can be the raw material on which
genetic drift operates.

Question 42

(C) Is inheritance (i.e., the presence of genetic variation) a necessary condition for evolution by
natural selection? Explain your answer briefly. (3 points)

Answer 42

Answer: YES. Inheritance of the phenotypic variation is required for the influence of natural
selection to be transmitted between generations.

Question 43

(C) Is inheritance (i.e., the presence of genetic variation) a necessary condition for evolution by
natural selection? Explain your answer briefly. (3 points)

Answer 43

Answer: YES. Inheritance of the phenotypic variation is required for the influence of natural
selection to be transmitted between generations.

Question 44

(D) Is inheritance (i.e., the presence of genetic variation) a necessary condition for evolution by
genetic drift? Explain your answer briefly. (4 points)

Answer 44

Answer: YES. Genetic drift requires some pre-existing genetic variation within the population.
We must have multiple alleles for the relative frequency of different alleles to change over
time under the influence of drift.

Question 45

(E) Is differential mean expectation of reproductive success (i.e., differential fitness) a necessary condition for evolution by natural selection? Explain your answer briefly. (3 points)

Answer 45

Answer: YES. Differential fitness is the cause of changes in the relative frequency of different
genetic variants. (Genetic variants associated with higher fitness are favored, causing their
frequency within populations to increase.)

Question 46

F) Is differential mean expectation of reproductive success (i.e., differential fitness) a necessary condition for evolution by genetic drift? Explain your answer briefly. (4 points)

Answer 46

Answer: NO. Genetic drift does not rely on differential fitness; rather, it relies solely on chance
events that occur in finite populations to generate changes in allele frequencies. Even
genetic variants with exactly the same mean expectation of reproductive success can evolve
under the influence of genetic drift.

Question 47

1. Gregor Mendel’s work on the basis for inheritance showed:
   a. that it was possible for all individuals in a diploid, sexually reproducing population with random mating to be heterozygotes, without selection acting
   b. that evolution by natural selection could generate major adaptive evolution, even if it started with an initially very rare allele that was produced by mutation
   c. that just as the phenotype of offspring often reflected a ‘blending’ of the influences of many genes, the gametes formed during meiosis carried genetic factors that reflected the blending of the parents’ two alleles found at a single locus
   d. that evolution by natural selection would be strengthened by the blending process that occurs during inheritance, because offspring would attain phenotypes intermediate between those of the parents
   e. a – d are all true statements

Answer 47

b. that evolution by natural selection could generate major adaptive evolution, even if it started with an initially very rare allele that was produced by mutation

Question 48

2. A female Drosophila fly is a double heterozygote with genotype A1A2B1B2, having inherited alleles A1 and B1 from its mother, and alleles A2 and B2 from its father. The A and B genes are located very close together on the same chromosome. If we sample the eggs produced by this female fly, we will
   see:
   a. eggs carrying A1B1, A1B2, A2B1, and A2B2, all at approximately equal frequencies
   b. only eggs carrying A1B1 and A2B2, at approximately equal frequencies
   c. only eggs carrying A1A2, and B1B2, at approximately equal frequencies
   d. eggs carrying A1B1, A1B2, A2B1, and A2B2, but with eggs carrying A1B1 and A2B2 being much more common than eggs carrying either A1B2 or A2B1.
   e. eggs carrying A1B1, A1B2, A2B1, and A2B2, but with eggs carrying A1B1 and A2B2 being less common than eggs carrying either A1B2 or A2B1.

Answer 48

d. eggs carrying A1B1, A1B2, A2B1, and A2B2, but with eggs carrying A1B1 and A2B2 being much more common than eggs carrying either A1B2 or A2B1.

Question 49

Assume a locus with two alleles, B and b, where b is a recessive lethal. Recessive lethal alleles like b are typically found at low, but stable frequencies in natural populations. Natural selection does not push the frequency of these alleles to zero because:
a. selection acts only against the heterozygotes (Bb) and mutation continues to produce more
recessive lethal alleles, b
b. selection acts only against the recessive homozygotes (bb), and mutation continues to produce
more recessive lethal alleles, b
c. selection cannot act against recessive lethals, because they are immediately removed from the
population (they die before reproducing)
d. the dominant allele B is hidden from selection when present in heterozygotes (Bb)
e. genetic drift prevents low frequency alleles like b from being lost from the population

Answer 49

b. selection acts only against the recessive homozygotes (bb), and mutation continues to produce

Question 50

Assume a locus with two alleles, B and b, where b is a recessive lethal. Recessive lethal alleles like b are typically found at low, but stable frequencies in natural populations. Natural selection does not push the frequency of these alleles to zero because:
a. selection acts only against the heterozygotes (Bb) and mutation continues to produce more
recessive lethal alleles, b
b. selection acts only against the recessive homozygotes (bb), and mutation continues to produce
more recessive lethal alleles, b
c. selection cannot act against recessive lethals, because they are immediately removed from the
population (they die before reproducing)
d. the dominant allele B is hidden from selection when present in heterozygotes (Bb)
e. genetic drift prevents low frequency alleles like b from being lost from the population

Answer 50

b. selection acts only against the recessive homozygotes (bb), and mutation continues to produce

Question 51

4. You are studying selection at a single locus with two alleles T (dominant) and t (recessive). The tt homozygote has reduced fitness relative to genotypes TT and Tt. If s, the selection coefficient for selection acting against genotype tt, is much less than 1/N, where N = population size, then
   a. changes in the frequency of allele t in the population will be dominated by natural selection over
   the long term (hundreds of generations), because random effects will tend to ‘average out’ over
   time
   b. changes in the frequency of allele t in the population will be dominated by natural selection over the long term (hundreds of generations), because random effects will tend to ‘average out’ across
   the N different members of the population
   c. changes in the frequency of allele t in the population will be dominated by genetic drift
   d. only genotypes with higher mean fitness (genotypes TT and Tt) will be able to increase in fitness
   e. the allele (T) will consistently increase in frequency until it displaces the t allele (allele T will go to
   ‘fixation’)

Answer 51

c. changes in the frequency of allele t in the population will be dominated by genetic drift

Question 52

The Argentine ant went through at least two genetic bottlenecks as it was introduced first from Argentina to New Orleans, and then from New Orleans to California. As a result of this, Argentine ants lost much of their genetic variation. A consequence of the lost variation is
a. a loss of competitive ability, apparently because the genetic uniformity of the ant populations
makes it more difficult for them to adapt to novel stresses, including pathogens
b. a loss of the ability to distinguish nestmates from non-nestmates, resulting in high levels of
aggression being expressed towards all other ants
c. unicoloniality, in which Argentine ants treat nearly all other Argentine ants as if they were members of the same colony
d. that even different ants within the same colony have different blends of waxy compounds on the
outside of their bodies
e. a persistently low ant population, whose evolution is therefore dominated by the effects of genetic
drift

Answer 52

c. unicoloniality, in which Argentine ants treat nearly all other Argentine ants as if they were members of the same colony

Question 53

6. Which of the following is NOT a key element of the ‘high-dose, refuge’ strategy for slowing the evolution of resistance to crop plants that express a protein toxin derived from Bacillus thuringiensis
   a. strong immigration of susceptible individuals from a nearby crop field that does not produce the protein toxin
   b. a dose of the toxin that is high enough to kill individuals with genotype RS (i.e., heterozygotes
   carrying one resistance-conferring allele and one susceptibility-conferring allele)
   c. matings between rare RR individuals and SS individuals, producing RS offspring
   d. a dose of the toxin that is high enough to kill RS individuals and most of the rare RR individuals
   e. a – d are ALL key elements of the ‘high-dose, refuge’ strategy

Answer 53

d. a dose of the toxin that is high enough to kill RS individuals and most of the rare RR individuals v

Question 54

7. When a single species of spadefoot toad (Spea multiplicata or Spea bombifrons) is found alone in a pond, such that there is no interspecific competition with the other spadefoot toad species, ecologists
   often observe:
   a. directional selection favoring individuals with small jaws, smooth mouthparts, and long guts
   b. directional selection favoring individuals with larger jaws, mouthparts with large tooth-like
   projections, and short guts
   c. stabilizing selection favoring individuals that have intermediate sized jaws, mouthparts with small tooth-like projections, and intermediate-length guts
   d. disruptive selection favoring either individuals with (1) small jaws, smooth mouthparts, and long guts, or (2) large jaws, mouthparts with large tooth-like projections, and short guts
   e. a – d are ALL realistic possibilities for spadefoot toad populations that are found

Answer 54

d. disruptive selection favoring either individuals with (1) small jaws, smooth mouthparts, and long guts, or (2) large jaws, mouthparts with large tooth-like projections, and short guts

Question 55

8. The Lotka-Volterra model of predator (P) - prey (N) dynamics is as follows:

In the second equation, the parameter f stands for

a. the frequency of interactions between predators and prey
b. the probability of an attack, given an encounter between a predator and a prey
c. the death rate imposed on the prey population by predator attacks
d. the final density of prey attained after the predator and prey populations reach an equilibrium
e. the efficiency with which predators convert consumed prey into their own offspring production

Answer 55

e. the efficiency with which predators convert consumed prey into their own offspring production

Question 56

Periodical cicadas are insects that have very unusual life cycles: in a given area, immature cicadas feed underground on the roots of trees, where they are protected from predators. Slowly, over a 17-year period, they develop to reach the adult stage. Then, all the adult cicadas emerge from the soil synchronously, often in huge numbers, and fly around to mate and lay eggs in the twigs of trees. The
density of adult cicadas is so large that predators that eat cicadas rapidly become satiated. The cicada offspring hatch from the eggs, drop to the ground, and spend the next 17 years below ground. Until the next emergence, there are no adult cicadas present at the site (the life cycles are perfectly synchronized across the entire population). This life cycle is directly analogous to (i.e., shares key
features with) which of the following life cycles:
a. senescence in a population of long-lived trees
b. reproduction by fission or budding in asexually reproducing corals or plants
c. masting in plant populations
d. phenotypic plasticity in a plant population experiencing different environmental conditions
e. a perfectly balanced harvest of essential resources, including light and water, by a plant

Answer 56

c. masting in plant populations

Question 57

1. Mendel’s First Law (law of segregation) was important to the ‘modern synthesis’ because it showed that
   a. inheritance was particulate, which is essential for natural selection to be effective
   b. polygenic traits produce a phenotype distribution that is nearly continuous
   c. several genes can produce an effect on the phenotype that looks like ‘blending’
   d. genetic recombination can make multiple genes present on the same chromosome assort
   independently
   e. none of the above is true

Answer 57

a. inheritance was particulate, which is essential for natural selection to be effective

Question 58

2. Mendel’s Second Law (law of independent assortment) states that
   a. inheritance operates through a blending process
   b. genes located on different pairs of homologous chromosomes assort independently during meiosis
   c. gamete frequencies are independent of the associated genotype frequencies
   d. all life forms are derived from a single origin of life
   e. none of the above is true

Answer 58

b. genes located on different pairs of homologous chromosomes assort independently during meiosis

Question 59

3. Genetic recombination
   a. occurs within chromosomes, through crossing over
   b. occurs across chromosomes, through meiosis and fertilization (normal sexual reproduction)
   c. occurs only when a new combination of alleles is needed for evolution to occur
   d. occurs only in small populations, in which drift is unimportant
   e. both a and b are correct

Answer 59

e. both a and b are correct

Question 60

Genes are said to be “linked” when they

a. affect the same phenotype
b. reside close to one another on the same chromosome
c. exhibit dominant and recessive alleles
d. satisfy Mendel’s 2nd Law (independent assortment)
e. are moved from one population to another by gene flow (migration)

Answer 60

b. reside close to one another on the same chromosome

Question 61

.When Darwin proposed his theory of evolution by natural selection, he lacked a clear understanding of
the mechanism of inheritance. This was a problem for his theory because
a. if inheritance occurred through a particulate mechanism, natural selection would be ineffective in
producing evolutionary change
b. if inheritance occurred through a blending mechanism, natural selection would be ineffective in producing evolutionary change
c. Lamarck demonstrated conclusively that acquired characteristics are inherited
d. meiosis makes it unlikely that offspring can resemble their parents
e. none of the above is true

Answer 61

b. if inheritance occurred through a blending mechanism, natural selection would be ineffective in producing evolutionary change

Question 62

2. Assume that in a diploid, sexually reproducing population with random mating we have a locus with
   two alleles, A1 and A2. Assume that the A1 allele produces high trait values and the A2 allele produces
   low trait values, such that genotype A1A1 produces a trait value of 10, genotype A1 A2 produces a trait
   value of 5, and genotype A2A2 produces a trait value of 0. Assume further that fitness is highest when
   the trait value = 5, and decreases symmetrically for either higher or lower trait values such that:
   Fitness for an individual with trait value 10 = 0.2
   Fitness for an individual with trait value 5 = 1.0
   Fitness for an individual with trait value 0 = 0.2

Answer 62

(A) Assume that the initial frequency of the A1 allele is 0.99, and the initial frequency of the A2 allele is 0.01. Will natural selection work more effectively (producing a population with a higher
average reproductive success) if we can ‘magically’ make inheritance operate through (i) a blending or (ii) a particulate mode of inheritance? Explain your answer briefly.

Question 63

Mutation

a. is too rare a process to produce a large amount of genetic variation
b. can only contribute to genetic variation if migration and recombination are occurring
c. acts similarly to genetic drift to remove genetic variation from populations
d. often occurs during DNA replication
e. usually produces all possible genotypes in a typical, large population

Answer 63

d. often occurs during DNA replication

Question 64

2. Mutation
   a. is the most important source of genetic variation
   b. produces heritable genetic variation when it occurs in the somatic cell lines
   c. is a rare process, and therefore plays a minor role in evolution
   d. is the cause of independent assortment
   e. is the cause of autosomal linkage

Answer 64

a. is the most important source of genetic variation

Question 65

3. Which of the following is NOT an assumption underlying the Hardy-Weinberg equilibrium
   a. very large (‘infinite’) population size
   b. assortative mating
   c. no selection
   d. no mutation
   e. no migration

Answer 65

b. assortative mating

Question 66

.Selection acting against a recessive lethal allele will
a. rapidly drive the allele frequency to zero, because selection is so strong (s = 1)
b. produce equilibrium genotype frequencies that are predicted by the Hardy-Weinberg
equilibrium
c. generate increased genetic variability in the population, much like mutation
d. produce the most rapid changes in allele frequencies when the initial frequency of the
recessive allele is low
e. none of the above is true

Answer 66

e. none of the above is true

Question 67

2. Selection against a harmful recessive allele (“a”) and in favor of a dominant allele (“A”)
   proceeds very slowly once the recessive allele is rare because:
   a. assortative mating generates many recessive homozygotes
   b. the Aa heterozygote has a reduced fitness compared to the AA genotype
   c. the fitness disadvantage of the aa genotype gets smaller as the “a” allele gets more rare
   d. the fitness cost of the “a” allele is hidden from selection when it is present in Aa individuals
   e. selection is offset by the effects of genetic drift

Answer 67

d. the fitness cost of the “a” allele is hidden from selection when it is present in Aa individuals

Question 68

Genetic drift

a. results in all individuals becoming heterozygotes
b. is most important when mutation rates are high
c. is most important when mutation rates are low
d. is most important when population size is small
e. none of the above is true

Answer 68

d. is most important when population size is small

Question 69

Which of the following can NOT be a source of novel genetic variants upon which natural 
selection can act 
a.  genetic drift 
b.  mutation 
c.  genetic recombination   
d.  gene flow

Answer 69

a. genetic drift

Question 70

3. Which of the following is NOT a process that can strengthen the influence of genetic drift on
   allele frequency changes
   a. random mating
   b. a population bottleneck following a disease epidemic
   c. a population bottleneck following a hurricane or other natural disaster
   d. low population size, as observed in endangered species
   e. a founder event v

Answer 70

a. random mating

Question 71

1. Disruptive selection and stabilizing selection
   a. both change the mean of the trait frequency distribution without changing the variance
   b. both decrease the variance of the trait frequency distribution
   c. both increase the variance of the trait frequency distribution
   d. have opposite effects on the mean of the frequency distribution
   e. none of the above is true

Answer 71

e. none of the above is true

Question 72

Phenotypic differences between identical twins demonstrate
a. that meiosis produces gametes that are genetically diverse
b. that independent assortment of genes on different chromosomes is one source of genetic
diversity
c. that environmental effects can generate phenotypic variation
d. that natural selection can operate during embryonic development
e. all of the above are true

Answer 72

c. that environmental effects can generate phenotypic variation

Question 73

3. The frequency distributions of phenotypic traits are often well-described by a bell-shaped
   curve because
   a. variation is often controlled primarily by two alleles, one dominant and one recessive
   b. environmental effects can produce variation in trait value
   c. many genes can contribute to variation in trait value
   d. b and c are both true
   e. none of the above is true

Answer 73

d. b and c are both true

Question 74

If you conduct a “common garden” experiment in which environmental variation is eliminated
perfectly, and you grow a sample of plants for which VG = 0, then:
a. heritability will be near 0.0
b. heritability will be near 0.5
c. heritability will be near 1.0
d. VP will be 0.0 and heritability will

Answer 74

d. VP will be 0.0 and heritability will

Question 75

Disruptive selection on a trait
a. tends to increase the variance in that trait and have little effect on the mean value of the
trait
b. tends to decrease the variance in that trait and have little effect on the mean value of the
trait
c. has little effect on the variance and a major effect on the mean
d. has no effect on either the mean or the variance, because the selection is balanced
e. has an effect essentially the same as stabilizing selection

Answer 75

a. tends to increase the variance in that trait and have little effect on the mean value of the
trait

Question 76

If you allow strong directional selection to act on a trait (like body size) in a population of
animals that are all clonally related to one another (VG = 0, and therefore VP = VE) you should
expect to see:
a. no change in either the mean or variance of the trait
b. an increase in the mean, with little change in the variance of the trait
c. an increase in the mean and a decrease in the variance of the trait
d. no change in the mean, but a decrease in the variance of the trait
e. no change in the mean, but an increase in the variance of the trait

Answer 76

a. no change in either the mean or variance of the trait

Question 77

7. Random mating can produce low-fitness intermediate phenotypes when
   a. stabilizing selection is acting on the population
   b. directional selection is acting on the population
   c. disruptive selection is acting on the population
   d. gene flow is operating
   e. the population is very small, and drift becomes a powerful evolutionary force

Answer 77

c. disruptive selection is acting on the population

Question 78

Predatory insects appear to evolve resistance to insecticides less frequently than do insect
herbivores. This can be explained as follows:
a. only herbivores and not predators have detoxification enzymes capable of breaking down
insecticides into non-toxic compounds
b. only predators and not herbivores can evolve resistance by evolving a new, insensitive
‘target site’ for the insecticide
c. herbivores that survive exposure to an insecticide may have a low fitness, because they will have limited opportunities to feed
d. predators that survive exposure to an insecticide may have a low fitness, because their insect prey population may be eliminated by the insecticide
e. the mutation rate in predator populations may be higher than in herbivore populations

Answer 78

d. predators that survive exposure to an insecticide may have a low fitness, because their insect prey population may be eliminated by the insecticide

Question 79

2. Insect pests that evolve resistance to insecticides impose new costs on human societies because
   a. greater doses or more frequent insecticide applications may be needed to control them
   b. an insecticide that is more expensive than the one originally used may need to be used
   for their control
   c. greater amounts of insecticide use needed to control resistant insects may generate
   greater impacts on the environment
   d. it may be impossible to control resistant insects, which can then create problems for
   human health and food production
   e. all of the above are true

Answer 79

e. all of the above are true

Question 80

3. The bacterium Bacillus thuringiensis
   a. produces a protein that is toxic to some insects but not to vertebrates
   b. produces a toxin that is activated in the low-pH gut of many vertebrates
   c. lives only inside the guts of insect hosts
   d. produces a toxin to which insects have never evolved resistance
   e. none of the above is true

Answer 80

a. produces a protein that is toxic to some insects but not to vertebrates

Question 80

3. The bacterium Bacillus thuringiensis
   a. produces a protein that is toxic to some insects but not to vertebrates
   b. produces a toxin that is activated in the low-pH gut of many vertebrates
   c. lives only inside the guts of insect hosts
   d. produces a toxin to which insects have never evolved resistance
   e. none of the above is true

Answer 80

a. produces a protein that is toxic to some insects but not to vertebrates

Question 81

2. Which of the following is NOT a way in which predators might DECREASE the
   population growth rate of their prey by
   a. increasing the prey population’s death rate
   b. decreasing the prey population’s birth rate
   c. increasing the prey population’s emigration rate
   d. decreasing the per capita rate of immigration to the prey population
   e. all of the above are true

Answer 81

e. all of the above are true