Question 1

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

Accepted Answer

Stabilizing selection occurs when natural selection favors the average or intermediate phenotype, while selecting against phenotypes at both extremes. In this case, starlings producing four to five eggs have the highest fitness, while those producing fewer or more eggs have reduced fitness. This is an example of stabilizing selection.

Question 2

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.

Accepted Answer

The founder effect occurs when a small group of individuals separates from a larger population and establishes a new colony with a limited gene pool. In the case of the island of Hawaii, it was formed from volcanic activity and therefore did not have a preexisting population. As a result, the evolution of life on this new island would have been influenced by the founder effect.

Question 3

Please use the following information to answer the questions below.
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 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

Accepted Answer

Combining moderate doses of nucleoside analogs (NA) and two different protease inhibitors (PI) targets multiple steps in the HIV life cycle, reducing the chance for resistance to develop compared to monotherapy or short-term treatments.

Question 4

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.

Accepted Answer

Stabilizing selection favors the heterozygous individuals and selects against the homozygous ones, leading to a decrease in the frequency of both homozygotes and an increase in the frequency of heterozygotes. However, since the gene is incompletely dominant, the heterozygous individuals will always express some phenotypic traits of both homozygotes, making it advantageous to maintain a certain proportion of heterozygotes in the population. Therefore, the proportion of the population that is heterozygous at this locus should remain constant over many generations. The population's average heterozygosity should also remain stable, as there is a balanced ratio of both homozygotes and heterozygotes.

Question 5

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.

Accepted Answer

The ongoing conflict between bacteria and bacteriophages results from frequency-dependent selection, as the prevalence of one trait (e.g., methylated DNA in bacteria or methylated genomes in bacteriophages) affects the selective advantage of another trait (e.g., unmethylated DNA in bacteria or unmethylated genomes in bacteriophages). This creates a cycling pattern of selection that ultimately maintains genetic diversity in both populations. The other options, such as evolutionary imbalance, heterozygote advantage, or neutral variation, do not fully capture the dynamics of this co-evolutionary process.

Question 6

Figure 21.3
In a very large population,a quantitative trait has the distribution pattern shown in 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?
A)immigration or emigration only
B)genetic drift only
C)directional selection and adaptation
D)genetic drift and disruptive selection
E)immigration or emigration,directional selection,and adaptation

Accepted Answer

If the curve shifts to the left or right, it indicates directional selection and adaptation. This means that certain traits are becoming more advantageous and being selected for, which would cause the shift in the distribution pattern. There is no indication of genetic drift or immigration/emigration in the question. Disruptive selection is not a correct answer because it would result in a bimodal distribution, with peaks at both ends of the graph, rather than a unimodal distribution with a shift to one side.

Question 7

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

Accepted Answer

Heterozygote advantage, also known as balancing selection, occurs when an individual who is heterozygous for a particular trait has a higher fitness than both the homozygotes. Stabilizing selection favors the heterozygotes, as they are better adapted to the intermediate range of the trait(s) being selected for, while the homozygotes on either extreme are under selection pressure. Sexual selection, directional selection, and disruptive selection are not necessarily linked to heterozygote advantage. Random selection does not favor any genotype over another, so it is not relevant to the concept of heterozygote advantage.

Question 8

Identify the statement that describes the imperfection of natural selection.
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.

Accepted Answer

Natural selection works by modifying existing structures rather than creating new ones from scratch, which can lead to imperfections in the adaptations of organisms.

Question 9

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.

Accepted Answer

The trend towards decreasing larynx size in adult females and increasing larynx size in adult males suggests that sexual dimorphism was developing over time in these species. This is because sexual dimorphism refers to the physical differences between males and females of the same species resulting from sexual selection. In this case, the increasing larynx size in males could have been a result of sexual selection, where females may have preferred males with deeper voices as an indication of their physical fitness. Alternatively, it could have been a result of intersexual selection, where males competed with each other for access to females with the deeper voice being an advantage.

Question 10

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

Accepted Answer

Gene duplication through translocation occurs when a segment of a gene detaches and then reattaches to a different location within the genome. In this scenario, the detachment of two genes from one RNA molecule and their attachment to the end of the other RNA molecule within the same HIV particle results in one of the RNA molecules having additional genetic material, hence a gene duplication event due to translocation. There is no increase or decrease in the total number of genes within the viral particle, nor is there a point substitution mutation, which would involve a change in a single nucleotide.

Question 11

Please use the following information to answer the question(s)below.
 
-Examining the figure,which type of selection has two peaks of frequency of individuals?
A)directional selection
B)disruptive selection
C)stabilizing selection
D)natural selection

Accepted Answer

Disruptive selection is characterized by two peaks of frequency of individuals at opposite ends of the spectrum, favoring extreme phenotypes over intermediate ones.

Question 12

Which of the following is most likely to produce an African butterfly species in the wild whose members have one pattern?
A)artificial selection
B)directional selection
C)stabilizing selection
D)disruptive selection

Accepted Answer

Stabilizing selection favors the intermediate phenotype in a population, and can result in fewer variations in appearance. In the case of African butterfly species, if there were individuals with different patterns (e.g. spotted and striped), stabilizing selection would favor those with patterns that were more similar to each other, resulting in the population having one dominant pattern.

Question 13

Please use the following information to answer the questions below.
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.

Accepted Answer

If the frequency of the recessive trait (aa) has not changed over time, it suggests that there is no selective advantage or disadvantage associated with either phenotype under laboratory conditions. Therefore, it can be concluded that the two phenotypes are about equally adaptive. This is supported by the fact that heterozygotes are indistinguishable from homozygous dominants, indicating that the dominant allele is not completely dominant.

Question 14

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)

Accepted Answer

The answer of Anopheles mosquitoes,which carry the malaria parasite,cannot live...

Question 15

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

Accepted Answer

Since UV light penetrates deeper into water than blue light, the fish with the allele for UV sensitive photopigment will have an advantage in locating themselves where they can see best. Therefore, over time, the frequency of the UV-sensitive allele should increase in the population compared to the blue-sensitive allele. This is depicted by the shift in the graph towards the right in option B, which shows higher frequency of the UV-sensitive allele at deeper depths.

Question 16

Sexual dimorphism is most often a result of
A)pansexual selection.
B)stabilizing selection.
C)intrasexual selection.
D)intersexual selection.
E)artificial selection.

Accepted Answer

Sexual dimorphism is most often a result of intersexual selection, where individuals of one sex choose mates based on specific traits of the other sex. This can lead to the evolution of exaggerated and distinct physical or behavioral characteristics in one sex that enhance their ability to attract and compete for mates.

Question 17

Please use the following information to answer the question(s)below.
 
-Examining the figure,which type of selection eliminates extreme frequency of individuals' phenotype?
A)directional selection
B)disruptive selection
C)stabilizing selection
D)natural selection

Accepted Answer

Stabilizing selection eliminates extreme frequency of individuals' phenotype by favoring the intermediate phenotype.

Question 18

Mountains also have an unmatched power to drive human evolution.Starting tens of thousands of years ago,people moved to high altitudes,and there they experienced natural selection that has reworked their biology.In Tibet,for example,people have broader arteries and capillaries.In the Andes,they can dissolve more oxygen into their blood.These different traits of people who live in high altitudes illustrate
A)stabilizing evolution.
B)sexual selection.
C)adaptive evolution.
D)acclimatization.

Accepted Answer

The different traits exhibited by people living in high altitudes illustrate adaptive evolution, as their biology has been reworked through natural selection to better suit their environment. The other options do not fit as well - stabilizing evolution refers to a reduction in variation within a population, sexual selection involves the selection of certain traits for mating purposes rather than survival advantage, and acclimatization refers to a temporary physiological response to changes in the environment.

Question 19

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.

Accepted Answer

The presence of a maladaptive trait (crossed eyes) in a highly adaptive environment suggests that phenotype is often the result of compromise, or trade-offs between different traits. In this case, the coat pattern may provide a selective advantage, while the crossed eyes may be a disadvantage. This illustrates the complexity of natural selection and how it can act on multiple traits simultaneously. The other answer choices are not supported by the observations given.

Question 20

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.

Accepted Answer

In the scenario where all seeds become hard, only the large-billed birds would have an advantage and be able to effectively crack the seeds. This would cause the frequency of the large-billed birds to increase over time, while the small-billed birds would decrease in frequency. This type of selection is called directional selection, as it favors one extreme of a trait distribution over the other.

Quiz 21: The Evolution of Populations

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?

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

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

Identify the statement that describes the imperfection of natural selection.

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?

Please use the following information to answer the question(s) below. -Examining the figure,which type of selection has two peaks of frequency of individuals?

Which of the following is most likely to produce an African butterfly species in the wild whose members have one pattern?

Sexual dimorphism is most often a result of

Please use the following information to answer the question(s) below. -Examining the figure,which type of selection eliminates extreme frequency of individuals' phenotype?

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?