Deck 21: The Evolution of Populations

Question 1

Which statement about variation is true?

A) All phenotypic variation is the result of genotypic variation.
B) All genetic variation produces phenotypic variation.
C) All nucleotide variability results in neutral variation.
D) All new alleles are the result of nucleotide variability.
E) All geographic variation results from the existence of clines.

Answer 1

D

Question 2

Although each of the following has a better chance of influencing gene frequencies in small populations than in large populations, which one most consistently requires a small population as a precondition for its occurrence?

A) mutation
B) nonrandom mating
C) genetic drift
D) natural selection
E) gene flow

Answer 2

C

Question 3

How many of these statements regarding populations are true? 1. Mature males and females of a population can interbreed with each other.
2) Populations are sometimes geographically isolated from other populations.
3) Biological species are made up of populations.
4) Members of a population tend to be genetically more similar to each other than to members of other populations.
5) Populations have genomes, but not gene pools.

A) Only one of these statements is true.
B) Two of these statements are true.
C) Three of these statements are true.
D) Four of these statements are true.
E) All five of these statements are true.

Answer 3

D

Question 4

In a Hardy-Weinberg population with two alleles, A and a, that are in equilibrium, the frequency of the allele a is 0.3. What is the frequency of individuals that are homozygous for this allele?

A) 0.09
B) 0.49
C) 0.9
D) 9.0
E) 49.0

Question 5

Whenever diploid populations are in Hardy-Weinberg equilibrium at a particular locus

A) the allele's frequency should not change from one generation to the next, but its representation in homozygous and heterozygous genotypes may change.
B) natural selection, gene flow, and genetic drift are acting equally to change an allele's frequency.
C) this means that, at this locus, two alleles are present in equal proportions.
D) the population itself is not evolving, but individuals within the population may be evolving.

Question 6

Which variable is likely to undergo the largest change in value resulting from a mutation that introduces a new allele into a population at a locus for which all individuals formerly had been fully homozygous?

A) average heterozygosity
B) nucleotide variability
C) geographic variability
D) average number of loci

Question 7

In peas, a gene controls flower color such that R = purple and r = white. In an isolated pea patch, there are 36 purple-flowering plants and 64 white-flowering plants. Assuming Hardy-Weinberg equilibrium, what is the value of q for this population?

A) 0.36
B) 0.64
C) 0.75
D) 0.80

Question 8

The higher the proportion of loci that are "fixed" in a population, the lower is that population's

A) nucleotide variability only.
B) chromosome number only.
C) average heterozygosity only.
D) nucleotide variability, average heterozygosity, and chromosome number.
E) nucleotide variability and average heterozygosity.

Question 9

Evolution

A) must happen, due to organisms' innate desire to survive.
B) must happen whenever a population is not well adapted to its environment.
C) can happen whenever any of the conditions for Hardy-Weinberg equilibrium are not met.
D) requires the operation of natural selection.
E) requires that populations become better suited to their environments.

Question 10

Hardy-Weinberg equilibrium must occur in populations where

A) an allele remains fixed.
B) no genetic variation exists.
C) natural selection is not operating.
D) All three of the responses above are correct.
E) Only two of the responses above are correct.

Question 11

If, on average, 46% of the loci in a species' gene pool are heterozygous, then the average homozygosity of the species should be

A) 23%.
B) 46%.
C) 54%.
D) There is not enough information to say.

Question 12

In a Hardy-Weinberg population with two alleles, A and a, that are in equilibrium, the frequency of allele a is 0.2. What is the frequency of individuals that are heterozygous for this allele?

A) 0.002
B) 0.020
C) 0.04
D) 0.16
E) 0.32

Question 13

Which statement about the beak size of finches on the island of Daphne Major during prolonged drought is true?

A) Each bird evolved a deeper, stronger beak as the drought persisted.
B) Each bird's survival was strongly influenced by the depth and strength of its beak as the drought persisted.
C) Each bird that survived the drought produced only offspring with deeper, stronger beaks than seen in the previous generation.
D) The frequency of the strong-beak alleles increased in each bird as the drought persisted.

Question 14

In the formula for determining a population's genotype frequencies, the pq in the term 2pq is necessary because

A) the population is diploid.
B) heterozygotes can come about in two ways.
C) the population is doubling in number.
D) heterozygotes have two alleles.

Question 15

Rank the following one-base-point mutations (from most likely to least likely) with respect to their likelihood of affecting the structure of the corresponding polypeptide: 1. insertion mutation deep within an intron
2) substitution mutation at the third position of an exonic codon
3) substitution mutation at the second position of an exonic codon
4) deletion mutation within the first exon of the gene

A) 1, 2, 3, 4
B) 4, 3, 2, 1
C) 2, 1, 4, 3
D) 3, 1, 4, 2
E) 2, 3, 1, 4

Question 16

Which of the following is a true statement concerning genetic variation?

A) It is created by the direct action of natural selection.
B) It arises in response to changes in the environment.
C) It must be present in a population before natural selection can act upon the population.
D) It tends to be reduced by the processes involved when diploid organisms produce gametes.
E) A population that has a higher average heterozygosity has less genetic variation than one with a lower average heterozygosity.

Question 17

Over time, the movement of people on Earth has steadily increased. This has altered the course of human evolution by increasing

A) nonrandom mating.
B) geographic isolation.
C) genetic drift.
D) gene flow.

Question 18

In the formula for determining a population's genotype frequencies, the 2 in the term 2pq is necessary because

A) the population is diploid.
B) heterozygotes can come about in two ways.
C) the population is doubling in number.
D) heterozygotes have two alleles.

Question 19

In a Hardy-Weinberg population with two alleles, A and a, that are in equilibrium, the frequency of allele a is 0.1. What is the frequency of individuals with AA genotype?

A) 0.20
B) 0.32
C) 0.42
D) 0.81
E) Genotype frequency cannot be determined from the information provided.

Question 20

You sample a population of butterflies and find that 56% are heterozygous at a particular locus. What should be the frequency of the recessive allele in this population?

A) 0.07
B) 0.08
C) 0.09
D) 0.70
E) Allele frequency cannot be determined from this information.

Question 21

What is true of natural selection?

A) Natural selection is a random process.
B) Natural selection creates beneficial mutations.
C) The only way to eliminate harmful mutations is through natural selection.
D) Mutations occur at random; natural selection can preserve and distribute beneficial mutations.
E) Mutations occur when directed by the good of the species; natural selection edits out harmful mutations and causes populations to adapt to the beneficial mutations.

Question 22

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? Figure 21.1

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

Question 23

There are those who claim that the theory of evolution cannot be true because the apes, which are supposed to be closely related to humans, do not likewise share the same large brains, capacity for complicated speech, and tool-making capability. They reason that if these features are generally beneficial, then the apes should have evolved them as well. Which of these provides the best argument against this misconception?

A) Advantageous alleles do not arise on demand.
B) A population's evolution is limited by historical constraints.
C) Adaptations are often compromises.
D) Evolution can be influenced by environmental change.

Question 24

The restriction enzymes of bacteria protect the bacteria from successful attack by bacteriophages, whose genomes can be degraded by the restriction enzymes. The bacterial genomes are not vulnerable to these restriction enzymes because bacterial DNA is methylated. This situation selects for bacteriophages whose genomes are also methylated. As new strains of resistant bacteriophages become more prevalent, this in turn selects for bacteria whose genomes are not methylated and whose restriction enzymes instead degrade methylated DNA. Over the course of evolutionary time, what should occur?

A) Methylated DNA should become fixed in the gene pools of bacterial species.
B) Nonmethylated DNA should become fixed in the gene pools of bacteriophages.
C) Methylated DNA should become fixed in the gene pools of bacteriophages.
D) Methylated and nonmethylated strains should be maintained among both bacteria and bacteriophages, with ratios that vary over time.
E) Both the first and second responses are correct.

Question 25

A proficient engineer can easily design skeletal structures that are more functional than those currently found in the forelimbs of such diverse mammals as horses, whales, and bats. The actual forelimbs of these mammals do not seem to be optimally arranged because

A) natural selection has not had sufficient time to create the optimal design in each case, but will do so given enough time.
B) in many cases, phenotype is not merely determined by genotype, but by the environment as well.
C) though we may not consider the fit between the current skeletal arrangements and their functions excellent, we should not doubt that natural selection ultimately produces the best design.
D) natural selection is generally limited to modifying structures that were present in previous generations and in previous species.

Question 26

When imbalances occur in the sex ratio of sexual species that have two sexes (i.e., other than a 50:50 ratio), the members of the minority sex often receive a greater proportion of care and resources from parents than do the offspring of the majority sex. This is most clearly an example of

A) sexual selection.
B) disruptive selection.
C) balancing selection.
D) stabilizing selection.
E) frequency-dependent selection.

Question 27

Which of the following is most likely to produce an African butterfly species in the wild whose members have one of two strikingly different color patterns?

A) artificial selection
B) directional selection
C) stabilizing selection
D) disruptive selection
E) sexual selection

Question 28

Adult male humans generally have deeper voices than do adult female humans, which is the direct result of higher levels of testosterone causing growth of the larynx. If the fossil records of apes and humans alike show a trend toward decreasing larynx size in adult females and increasing larynx size in adult males, then

A) sexual dimorphism was developing over time in these species.
B) intrasexual selection seems to have occurred.
C) stabilizing selection was occurring in these species concerning larynx size.
D) selection was acting more directly upon genotype than upon phenotype.

Question 29

In the wild, male house finches (Carpodus mexicanus) vary considerably in the amount of red pigmentation in their head and throat feathers, with colors ranging from pale yellow to bright red. These colors come from carotenoid pigments that are found in the birds' diets; no vertebrates are known to synthesize carotenoid pigments. Thus, the brighter red the male's feathers are, the more successful he has been at acquiring the red carotenoid pigment by his food-gathering efforts (all other factors being equal). During breeding season, one should expect female house finches to prefer to mate with males with the brightest red feathers. Which of the following is true of this situation?

A) Alleles that promote more efficient acquisition of carotenoid-containing foods by males should increase over the course of generations.
B) Alleles that promote more effective deposition of carotenoid pigments in the feathers of males should increase over the course of generations.
C) There should be directional selection for bright red feathers in males.
D) Three of the statements are correct.
E) Two of the statements are correct.

Question 30

The restriction enzymes of bacteria protect the bacteria from successful attack by bacteriophages, whose genomes can be degraded by the restriction enzymes. The bacterial genomes are not vulnerable to these restriction enzymes because bacterial DNA is methylated. This situation selects for bacteriophages whose genomes are also methylated. As new strains of resistant bacteriophages become more prevalent, this in turn selects for bacteria whose genomes are not methylated and whose restriction enzymes instead degrade methylated DNA. The outcome of the conflict between bacteria and bacteriophage at any point in time results from

A) frequency-dependent selection.
B) evolutionary imbalance.
C) heterozygote advantage.
D) neutral variation.
E) genetic variation being preserved by diploidy.

Question 31

Most Swiss starlings produce four to five eggs in each clutch. Starlings producing fewer, or more, than this have reduced fitness. Which of the following terms best describes this situation?

A) artificial selection
B) directional selection
C) stabilizing selection
D) disruptive selection
E) sexual selection

Question 32

The same gene that causes various coat patterns in wild and domesticated cats also causes a cross-eyed condition in these cats, the cross-eyed condition being slightly maladaptive. In a hypothetical environment, the coat pattern that is associated with crossed eyes is highly adaptive, with the result that both the coat pattern and the cross-eyed condition increase in a feline population over time. Which statement is supported by these observations?

A) Evolution is progressive and tends toward a more perfect population.
B) Phenotype is often the result of compromise.
C) Natural selection reduces the frequency of maladaptive genes in populations over the course of time.
D) Polygenic inheritance is generally maladaptive, and should become less common in future generations.
E) In all environments, coat pattern is a more important survival factor than is eye-muscle tone.

Question 33

If the original finches that had been blown over to the Galápagos from South America had already been genetically different from the parental population of South American finches, even before adapting to the Galápagos, this would have been an example of

A) genetic drift.
B) the bottleneck effect.
C) the founder effect.
D) genetic drift and the founder effect.
E) all three of these.

Question 34

In seedcracker finches from Cameroon, small- and large-billed birds specialize in cracking soft and hard seeds, respectively. If long-term climatic change resulted in all seeds becoming hard, what type of selection would then operate on the finch population?

A) disruptive selection
B) directional selection
C) stabilizing selection
D) No selection would operate because the population is in Hardy-Weinberg equilibrium.

Question 35

Sexual dimorphism is most often a result of

A) pansexual selection.
B) stabilizing selection.
C) intrasexual selection.
D) intersexual selection.
E) artificial selection.

Question 36

The recessive allele that causes phenylketonuria (PKU) is harmful, except when an infant's diet has appropriate levels of the amino acid phenylalanine. What maintains the presence of this harmful allele in a population's gene pool?

A) heterozygote advantage
B) stabilizing selection
C) diploidy
D) balancing selection

Question 37

Heterozygote advantage should be most closely linked to which of the following?

A) sexual selection
B) stabilizing selection
C) random selection
D) directional selection
E) disruptive selection

Question 38

During breeding season, one should expect female house finches to prefer to mate with males with the brightest red feathers. Which of the following terms are appropriately applied to this situation?

A) sexual selection
B) mate choice
C) intersexual selection
D) Three of the responses are correct.
E) Two of the responses are correct.

Question 39

Arrange the following from most general (i.e., most inclusive) to most specific (i.e., least inclusive): 1. natural selection
2) microevolution
3) intrasexual selection
4) evolution
5) sexual selection

A) 4, 1, 2, 3, 5
B) 4, 2, 1, 3, 5
C) 4, 2, 1, 5, 3
D) 1, 4, 2, 5, 3
E) 1, 2, 4, 5, 3

Question 40

Which of the following statements best summarizes evolution as it is viewed today?

A) It represents the result of selection for acquired characteristics.
B) It is synonymous with the process of gene flow.
C) It is the descent of humans from the present-day great apes.
D) It is the differential survival and reproduction of the most-fit phenotypes.

Question 41

In the year 2500, five male space colonists and five female space colonists (all unrelated to each other) settle on an uninhabited Earthlike planet in the Andromeda galaxy. The colonists and their offspring randomly mate for generations. All 10 of the original colonists had free earlobes, and 2 were heterozygous for that trait. The allele for free earlobes is dominant to the allele for attached earlobes.
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

Question 42

Use the following information to answer the following questions.
In those parts of equatorial Africa where the malaria parasite is most common, the sickle-cell allele constitutes 20% of the β hemoglobin alleles in the human gene pool.
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

Question 43

Use this information to answer the following questions.
A large population of laboratory animals has been allowed to breed randomly for a number of generations. After several generations, 25% of the animals display a recessive trait (aa), the same percentage as at the beginning of the breeding program. The rest of the animals show the dominant phenotype, with heterozygotes indistinguishable from the homozygous dominants.
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.

Question 44

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.

Question 45

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?

A)

B)

C)

D)

Question 46

Use this information to answer the following questions.
You are studying three populations of birds. Population A has 10 birds, of which 1 is brown (a recessive trait) and 9 are red. Population B has 100 birds, of which 10 are brown. Population C has 30 birds, and 3 of them are brown.
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.

Question 47

In the year 2500, five male space colonists and five female space colonists (all unrelated to each other) settle on an uninhabited Earthlike planet in the Andromeda galaxy. The colonists and their offspring randomly mate for generations. All 10 of the original colonists had free earlobes, and 2 were heterozygous for that trait. The allele for free earlobes is dominant to the allele for attached earlobes.
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

Question 48

Use this information to answer the following questions.
You are studying three populations of birds. Population A has 10 birds, of which 1 is brown (a recessive trait) and 9 are red. Population B has 100 birds, of which 10 are brown. Population C has 30 birds, and 3 of them are brown.
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.

Question 49

Use the following information to answer the following questions.
In those parts of equatorial Africa where the malaria parasite is most common, the sickle-cell allele constitutes 20% of the β hemoglobin alleles in the human gene pool.
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.

Question 50

Use this information to answer the following questions.
A large population of laboratory animals has been allowed to breed randomly for a number of generations. After several generations, 25% of the animals display a recessive trait (aa), the same percentage as at the beginning of the breeding program. The rest of the animals show the dominant phenotype, with heterozygotes indistinguishable from the homozygous dominants.
What is the estimated frequency of allele A in the gene pool?

A) 0.25
B) 0.50
C) 0.75
D) 0.125

Question 51

Use this information to answer the following questions.
A large population of laboratory animals has been allowed to breed randomly for a number of generations. After several generations, 25% of the animals display a recessive trait (aa), the same percentage as at the beginning of the breeding program. The rest of the animals show the dominant phenotype, with heterozygotes indistinguishable from the homozygous dominants.
What proportion of the population is probably heterozygous (Aa) for this trait?

A) 0.05
B) 0.25
C) 0.50
D) 0.75

Question 52

Use the following information to answer the following questions.
In those parts of equatorial Africa where the malaria parasite is most common, the sickle-cell allele constitutes 20% of the β hemoglobin alleles in the human gene pool.
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

Question 53

Use the following information to answer the following questions.
In those parts of equatorial Africa where the malaria parasite is most common, the sickle-cell allele constitutes 20% of the β hemoglobin alleles in the human gene pool.
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

Question 54

Use the following information to answer the following questions.
In those parts of equatorial Africa where the malaria parasite is most common, the sickle-cell allele constitutes 20% of the β hemoglobin alleles in the human gene pool.
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

Question 55

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.

Question 56

Use Figure 21.2 to answer the following question.
Figure 21.2
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.

Question 57

Use the following information to answer the following questions.
In those parts of equatorial Africa where the malaria parasite is most common, the sickle-cell allele constitutes 20% of the β hemoglobin alleles in the human gene pool.
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.

Question 58

In a very large population, a quantitative trait has the distribution pattern shown in Figure 21.3.
Figure 21.3
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

Question 59

The following questions refer to the information in the following paragraph.
HIV's genome of RNA includes the code for reverse transcriptase (RT), an enzyme that acts early in infection to synthesize a DNA genome off of an RNA template. The HIV genome also codes for protease (PR), an enzyme that acts later in infection by cutting long viral polyproteins into smaller, functional proteins. Both RT and PR represent potential targets for antiretroviral drugs. Drugs called nucleoside analogs (NA) act against RT, whereas drugs called protease inhibitors (PI) act against PR.
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

Question 60

If global warming permits mosquitoes to live at higher altitudes than they currently do, then in which direction should the entire plot in the correct distribution below be shifted? a. b. c. d.

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.

Question 61

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

Question 62

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.

Question 63

In the year 2500, five male space colonists and five female space colonists (all unrelated to each other) settle on an uninhabited Earthlike planet in the Andromeda galaxy. The colonists and their offspring randomly mate for generations. All 10 of the original colonists had free earlobes, and 2 were heterozygous for that trait. The allele for free earlobes is dominant to the allele for attached earlobes.
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.

Question 64

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.

Question 65

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

Question 66

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.

Question 67

In the year 2500, five male space colonists and five female space colonists (all unrelated to each other) settle on an uninhabited Earthlike planet in the Andromeda galaxy. The colonists and their offspring randomly mate for generations. All 10 of the original colonists had free earlobes, and 2 were heterozygous for that trait. The allele for free earlobes is dominant to the allele for attached earlobes.
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.

Question 68

In the year 2500, five male space colonists and five female space colonists (all unrelated to each other) settle on an uninhabited Earthlike planet in the Andromeda galaxy. The colonists and their offspring randomly mate for generations. All 10 of the original colonists had free earlobes, and 2 were heterozygous for that trait. The allele for free earlobes is dominant to the allele for attached earlobes.
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.

Question 69

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.