Chapter 23 Biology

If the sickle-cell allele is recessive, what proportion of the population should be susceptible to sickle-cell anemia under typical conditions?

0.04

Which of these is closest to the allele frequency in the founding population?

0.1 a, 0.9 A

What should be the proportion of heterozygous individuals in populations that live here?

0.32

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?

0.42

What is the estimated frequency of allele A in the gene pool?

0.50

What proportion of the population is probably heterozygous (Aa) for this trait?

0.50

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?

0.80

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?

0.81

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 and 3

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?

100

If the curve in the previous figure 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?

2 and 3

Within the body of an HIV-infected individual who is being treated with a single NA, and whose HIV particles are currently vulnerable to this NA, which of these situations can increase the virus' relative fitness?

2 only

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 percentage of the population that is heterozygous for this allele?

32.0

Arrange the following from most general (i.e., most inclusive) to most specific (i.e., least inclusive):

4, 2, 1, 5, 3

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:

4, 3, 2, 1

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

54%.

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 percentage of the population that is homozygous for this allele?

9.0

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?

Advantageous alleles do not arise on demand.

HIV has nine genes in its RNA genome. Every HIV particle contains two RNA molecules, and each molecule contains all nine genes. If, for some reason, the two RNA molecules within a single HIV particle do not have identical sequences, then which of these terms can be applied due to the existence of the nonidentical regions?

All but one of the responses are correct.

Which statement about variation is true?

All new alleles are the result of nucleotide variability.

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?

Allele frequency cannot be determined from this information.

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

Blue light is that portion of the visible spectrum that penetrates the deepest 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 following graphs 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?

B

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

Each bird's survival was strongly influenced by the depth and strength of its beak as the drought persisted.

How many of these statements regarding populations are true?

Four of these statements are true.

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?

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

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

It is the differential survival and reproduction of the most-fit phenotypes.

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

It must be present in a population before natural selection can act upon the population.

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?

Methylated and nonmethylated strains should be maintained among both bacteria and bacteriophages, with ratios that vary over time.

What is true of natural selection?

Mutations occur at random; natural selection can preserve and distribute beneficial mutations.

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?

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

Hardy-Weinberg equilibrium must occur in populations wherein

Only two of the responses above are correct.

The same gene that causes various coat patterns in wild and domesticated cats also causes the 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?

Phenotype is often the result of compromise.

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?

The proportions of both types of homozygote should decrease.

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?

The two phenotypes are about equally adaptive under laboratory conditions.

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?

Three of the responses are correct.

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?

Three of the statements are correct.

A trend toward the decrease in the size of plants on the slopes of mountains as altitudes increase is an example of

a cline.

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

adaptations are often compromises.

Which of these variables is likely to undergo the largest change in value as the result of a mutation that introduces a brand-new allele into a population's gene pool at a locus that had formerly been fixed?

average heterozygosity

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

both the first and third of these.

Evolution

can happen whenever any of the conditions for Hardy-Weinberg equilibrium are not met.

During an individual organism's lifetime, which of these is most likely to help the organism respond properly to changes in its environment?

change in gene expression

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

cross your flies with flies from another lab.

The volcano is currently dormant, but in a hypothetical future scenario, satellite cones at the base of Mt. Kilimanjaro spew sulfurous gases and lava, destroying all life located between the base and 6,000 feet above sea level. As a result of this catastrophe, how should the frequency of the sickle-cell allele change in the remnant human population that survives above 6,000 feet, and which phenomenon accounts for this change in allele frequency?

decreases; bottleneck effect

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

diploidy

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?

directional selection

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?

directional selection; stabilizing selection

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?

disruptive selection

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 one excludes the involvement of gender in the situation, then the pattern that is apparent in the fossil record is most similar to one that should be expected from

disruptive selection.

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

frequency-dependent selection.

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

frequency-dependent selection.

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?

gene flow

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

gene flow.

The production of new types of flu virus in the manner described above is most similar to the phenomenon of

gene flow.

If the nucleotide variability of a locus equals 0%, what is the gene variability and number of alleles at that locus?

gene variability = 0%; number of alleles = 1

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?

genetic drift

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

genetic drift

There are 40 individuals in population 1, all with genotype A1A1, and there are 25 individuals in population 2, all with genotype A2A2. 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 is most likely an example of

genetic drift

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

heterozygotes can come about in two ways.

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

heterozygotes have two alleles.

Natural selection changes allele frequencies because some ________ survive and reproduce more successfully than others.

individuals

Sexual dimorphism is most often a result of

intersexual selection.

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

natural selection is generally limited to modifying structures that were present in previous generations and in previous species.

Most invertebrates have a cluster of ten similar Hox genes, all located on the same chromosome. Most vertebrates have four such clusters of Hox genes, located on four nonhomologous chromosomes. The process that could have potentially contributed to the cluster's presence on more than one chromosome was ________.

nondisjunction

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

nucleotide variability and average heterozygosity only.

Which population is most likely to be subject to the bottleneck effect?

population A

In which population would it be least likely that an accident would significantly alter the frequency of the brown allele?

population B

In modern terminology, diversity is understood to be a result of genetic variation. Which of the following is a recognized source of variation for evolution?

recombination by crossing over in meiosis

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

sexual dimorphism was developing over time in these species.

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

stabilizing selection

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?

stabilizing selection

What is true of the trait whose frequency distribution in a large population appears in the previous figure? It has probably undergone

stabilizing selection

Sparrows with average-sized wings survive severe storms better than those with longer or shorter wings, illustrating

stabilizing selection.

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

the allele's frequency should not change from one generation to the next, but its representation in homozygous and heterozygous genotypes may change.

No two people are genetically identical, except for identical twins. The main source of genetic variation among human individuals is

the reshuffling of alleles in sexual reproduction.

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?

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)?

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