Chapter 23 Practice Questions

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.

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

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.

D) 0.81

Hardy-Weinberg equilibrium must occur in populations wherein 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.

E) Only two of the responses above are correct.

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 b hemoglobin alleles in the human gene pool. 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

A) 0.04

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 ten of the original colonists had free earlobes, and two 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

A) 0.1 a, 0.9 A

The following questions refer to 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. 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.

A) The proportions of both types of homozygote should decrease.

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 A) genetic drift. B) gene flow. C) disruptive selection. D) discrete variation. E) directional selection.

A) genetic drift.

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.

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

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

B) stabilizing selection

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 b 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.

B) gene flow

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.

B) heterozygotes can come about in two ways.

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

C) 4, 2, 1, 5, 3

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.

C) 54%.

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.

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

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 ten of the original colonists had free earlobes, and two 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.

C) 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

D) 0.42

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.

D) Four of these statements are true.

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.

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

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.

D) gene flow.

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? A) 0.2 B) 2.0 C) 4.0 D) 16.0 E) 32.0

E) 32.0

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 b 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

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

E) frequency-dependent selection.

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

E) individuals