Blue light is a portion of the visible spectrum that penetrates deep into bodies of water.
Ultraviolet (UV) light, though, can penetrate even deeper. A gene within a population of marine
fish that inhabits depths from 500 m to 1,000 m has an allele for a photopigment that is sensitive
to UV light, and another allele for a photopigment that is sensitive to blue light. Which of the
graphs in Figure 21.1 best depicts the predicted distribution of these alleles within a population if
the fish that carry these alleles prefer to locate themselves where they can see best?

A) A
B) B
C) C
D) D

B

Anopheles mosquitoes, which carry the malaria parasite, cannot live above elevations of 5,900
feet. In addition, oxygen availability decreases with higher altitude. Consider a hypothetical
human population that is adapted to life on the slopes of Mt. Kilimanjaro in Tanzania, a country
in equatorial Africa. Mt. Kilimanjaro's base is about 2,600 feet above sea level and its peak is
19,341 feet above sea level. If the incidence of the sickle-cell allele in the population is plotted
against altitude (feet above sea level), which of the following distributions is most likely,
assuming little migration of people up or down the mountain?

B

Soon after the island of Hawaii rose above the sea surface (somewhat less than 1 million years
ago), the evolution of life on this new island should have been most strongly influenced by
A) genetic bottleneck.
B) sexual selection.
C) habitat differentiation.
D) founder effect.

founder effect

If the curve in Figure 21.3 shifts to the left or to the right, there is no gene flow, and the
population size consequently increases over successive generations. Which of the following is
(are) probably occurring?
1. immigration or emigration
2. directional selection
3. adaptation
4. genetic drift
5. disruptive selection
A) 1 only
B) 4 only
C) 2 and 3
D) 4 and 5
E) 1, 2, and 3

2 and 3

A) Curve A will be shifted to the right.
B) Curve B will be shifted to the right.
C) Curve C will be shifted upward.
D) Curve D will be shifted upward.

Curve B will be shifted to the right

Which of the following represents the treatment option most likely to avoid the production of
drug-resistant HIV (assuming no drug interactions or side effects)?
A) using a series of NAs, one at a time, and changed about once a week
B) using a single PI, but slowly increasing the dosage over the course of a week
C) using high doses of NA and a PI at the same time for a period not to exceed one day
D) using moderate doses of NA and two different PIs at the same time for several months

using moderate doses of NA and two different PIs at the same time for several months

Every HIV particle contains two RNA molecules. If two genes from one RNA molecule
become detached and then, as a unit, get attached to one end of the other RNA molecule within a
single HIV particle, which of these is true?
A) There are now fewer genes within the viral particle.
B) There are now more genes within the viral particle.
C) A point substitution mutation has occurred in the retroviral genome.
D) The retroviral equivalent of crossing over has occurred, no doubt resulting in a heightened
positive effect.
E) One of the RNA molecules has experienced gene duplication as the result of translocation.

One of the RNA molecules has experienced gene duplication as the result of translocation.

In a hypothetical population's gene pool, an autosomal gene, which had previously been fixed,
undergoes a mutation that introduces a new allele, one inherited according to incomplete
dominance. Natural selection then causes stabilizing selection at this locus. Consequently, what
should happen over the course of many generations?
A) The proportions of both types of homozygote should decrease.
B) The proportion of the population that is heterozygous at this locus should remain constant.
C) The population's average heterozygosity should decrease.
D) The two homozygotes should decrease at different rates.

The proportion of the population that is heterozygous at this locus should remain constant.

What is the most reasonable conclusion that can be drawn from the fact that the frequency of
the recessive trait (aa) has not changed over time?
A) The population is undergoing genetic drift.
B) The two phenotypes are about equally adaptive under laboratory conditions.
C) The genotype AA is lethal.
D) There has been a high rate of mutation of allele A to allele a.
E) There has been sexual selection favoring allele a.

The two phenotypes are about equally adaptive under laboratory conditions.

What is the estimated frequency of allele A in the gene pool?
A) 0.25
B) 0.50
C) 0.75
D) 0.125

0.50

What proportion of the population is probably heterozygous (Aa) for this trait?
A) 0.05
B) 0.25
C) 0.50
D) 0.75

0.50

In which population would it be least likely that an accident would significantly alter the
frequency of the brown allele?
A) population A
B) population B
C) population C
D) They are all the same.
E) It is impossible to tell from the information given.

population B

Which population is most likely to be subject to the bottleneck effect?
A) population A
B) population B
C) population C
D) They are all equally likely.
E) It is impossible to tell from the information given.

population A

With respect to the sickle-cell allele, what should be true of the β hemoglobin locus in U.S.
populations of African-Americans whose ancestors were from equatorial Africa?
1. The average heterozygosity at this locus should be decreasing over time.
2. There is an increasing heterozygote advantage at this locus.
3. Diploidy is helping to preserve the sickle-cell allele at this locus.
4. Frequency-dependent selection is helping to preserve the sickle-cell allele at this locus.
A) 1 only
B) 1 and 3
C) 2 and 3
D) 1, 2, and 3
E) 1, 2, and 4

1 and 3

Although selection is clearly present, if the ideal equilibrium of alleles existed, what should
be the proportion of heterozygous individuals in populations that live here?
A) 0.04
B) 0.16
C) 0.20
D) 0.32
E) 0.80

0.32

Again, if this population were in equilibrium and if the sickle-cell allele is recessive, what
proportion of the population should be susceptible to sickle-cell anemia under typical conditions?
A) 0.04
B) 0.16
C) 0.20
D) 0.32
E) 0.80

0.04

12) Considering the overall human population of the U.S. mainland at the time when the slave
trade brought large numbers of people from equatorial Africa, what was primarily acting to
change the frequency of the sickle-cell allele in the overall U.S. population?
A) natural selection
B) gene flow
C) genetic drift
D) founder effect
E) Two of the responses are correct.

gene flow

The sickle-cell allele is pleiotropic (i.e., it affects more than one phenotypic trait).
Specifically, this allele affects oxygen delivery to tissues and affects one's susceptibility to
malaria. Under conditions of low atmospheric oxygen availability, individuals heterozygous for
this allele can experience life-threatening sickle-cell "crises." Such individuals remain less
susceptible to malaria. Thus, pleiotropic genes/alleles such as this can help explain why
A) new advantageous alleles do not arise on demand.
B) evolution is limited by historical constraints.
C) adaptations are often compromises.
D) chance events can affect the evolutionary history of populations.

adaptations are often compromises.

In the United States, the parasite that causes malaria is not present, but African-Americans
whose ancestors were from equatorial Africa are present. What should be happening to the
sickle-cell allele in the United States, and what should be happening to it in equatorial Africa?
A) stabilizing selection; disruptive selection
B) disruptive selection; stabilizing selection
C) disruptive selection; directional selection
D) directional selection; disruptive selection
E) directional selection; stabilizing selection

directional selection; stabilizing selection

Which of these is closest to the allele frequency in the founding population?
A) 0.1 a, 0.9 A
B) 0.2 a, 0.8 A
C) 0.5 a, 0.5 A
D) 0.8 a, 0.2 A
E) 0.4 a, 0.6 A

0.1 a, 0.9 A

If one assumes that Hardy-Weinberg equilibrium applies to the population of colonists on
this planet, about how many people will have attached earlobes when the planet's population
reaches 10,000?
A) 100
B) 400
C) 800
D) 1,000
E) 10,000

100

If four of the original colonists died before they produced offspring, the ratios of genotypes
could be quite different in the subsequent generations. This would be an example of
A) diploidy.
B) gene flow.
C) genetic drift.
D) disruptive selection.
E) stabilizing selection.

genetic drift.

You are maintaining a small population of fruit flies in the laboratory by transferring the flies
to a new culture bottle after each generation. After several generations, you notice that the
viability of the flies has decreased greatly. Recognizing that small population size is likely to be
linked to decreased viability, the best way to reverse this trend is to
A) cross your flies with flies from another lab.
B) reduce the number of flies that you transfer at each generation.
C) transfer only the largest flies.
D) change the temperature at which you rear the flies.
E) shock the flies with a brief treatment of heat or cold to make them more hardy.

cross your flies with flies from another lab.

Swine are vulnerable to infection by bird flu virus and human flu virus, which can both be
present in an individual pig at the same time. When this occurs, it is possible for genes from bird
flu virus and human flu virus to be combined. If the human flu virus contributes a gene for
Tamiflu resistance (Tamiflu is an antiviral drug) to the new virus, and if the new virus is
introduced to an environment lacking Tamiflu, then what is most likely to occur?
A) The new virus will maintain its Tamiflu-resistance gene, just in case of future exposure to
Tamiflu.
B) The Tamiflu-resistance gene will undergo mutations that convert it into a gene that has a
useful function in this environment.
C) If the Tamiflu-resistance gene involves a cost, it will experience directional selection leading
to reduction in its frequency.
D) If the Tamiflu-resistance gene confers no benefit in the current environment, and has no cost,
the virus will become dormant until Tamiflu is present.

If the Tamiflu-resistance gene involves a cost, it will experience directional selection leading
to reduction in its frequency.

Natural selection changes allele frequencies because some ________ survive and reproduce
more successfully than others.
A) alleles
B) loci
C) gene pools
D) species
E) individuals

individuals

No two people are genetically identical, except for identical twins. The main source of genetic
variation among human individuals is
A) new mutations that occurred in the preceding generation.
B) genetic drift due to the small size of the population.
C) the reshuffling of alleles in sexual reproduction.
D) natural selection.
E) environmental effects.

the reshuffling of alleles in sexual reproduction.

Sparrows with average-sized wings survive severe storms better than those with longer or
shorter wings, illustrating
A) the bottleneck effect.
B) disruptive selection.
C) frequency-dependent selection.
D) neutral variation.
E) stabilizing selection.

stabilizing selection.

If the nucleotide variability of a locus equals 0%, what is the gene variability and number of
alleles at that locus?
A) gene variability = 0%; number of alleles = 0
B) gene variability = 0%; number of alleles = 1
C) gene variability = 0%; number of alleles = 2
D) gene variability > 0%; number of alleles = 2
E) Without more information, gene variability and number of alleles cannot be determined.

gene variability = 0%; number of alleles = 1

There are 25 individuals in population 1, all with genotype AA, and there are 40 individuals in
population 2, all with genotype aa. Assume that these populations are located far from each other
and that their environmental conditions are very similar. Based on the information given here,
the observed genetic variation most likely resulted from
A) genetic drift.
B) gene flow.
C) disruptive selection.
D) nonrandom mating.
E) directional selection.

genetic drift.

A fruit fly population has a gene with two alleles, A1 and A2. Tests show that 70% of the
gametes produced in the population contain the A1 allele. If the population is in Hardy-Weinberg
equilibrium, what proportion of the flies carry both A1 and A2?
A) 0.7
B) 0.49
C) 0.21
D) 0.42
E) 0.09

0.42