Deck 23: Evolutionary Processes

Question 1

For a biologist studying a small fish population in the lab, which Hardy-Weinberg condition is easiest to meet?

A) no selection
B) no genetic drift
C) no gene flow
D) no mutation
E) random mating

Answer 1

C

Question 2

In all three species of phalarope, a taxon of wading shorebirds, the majority of parental care is provided by the male. Based on the Bateman-Trivers hypothesis of sexual selection, what would you expect to see in phalaropes?

A) Chick survival is very low.
B) Females are more brightly colored than males.
C) Each female mates with a single male.
D) Males are larger than females.

Answer 2

B

Question 3

Cystic fibrosis is a genetic disorder in homozygous recessives that causes death during the teenage years. If 9 in 10,000 newborn babies have the disease, what are the expected frequencies of the dominant (A1) and recessive (A2) alleles according to the Hardy-Weinberg model?

A) f(A1) = 0.9997, f(A2) = 0.0003
B) f(A1) = 0.9800, f(A2) = 0.0200
C) f(A1) = 0.9700, f(A2) = 0.0300
D) f(A1) = 0.9604, f(A2) = 0.0392
E) f(A1) = 0.9600, f(A2) = 0.0400

Answer 3

C

Question 4

Use the following information to answer the question(s) below.
Martin Wikelski and L. Michael Romero (Body size, performance, and fitness in Galápagos marine iguanas, Integrative and Comparative Biology 43 [2003]: 376-86) measured the snout-to-vent (anus) length of Galápagos marine iguanas and observed the percent survival of different-sized animals, all of the same age. The graph shows the log snout-vent length (SVL, a measure of overall body size) plotted against the percent survival of these different-size classes for males and females.
Wikelski and Romero (2003) found that large marine iguanas had higher reproductive success than smaller iguanas did. However, the large iguanas were generally in poor body condition because they could not eat enough; at higher temperatures, their foraging efficiency improved, allowing them to eat more. Thus, Wikelski and Romero hypothesized that iguana size will ________ as global warming gradually increases air and water temperatures in the Galápagos Islands.

A) increase
B) decrease
C) stabilize around the mean body size
D) remain unchanged (it is not clear that body size increases fitness)

Question 5

Which of the graphs shown best represents the relationship between the intensity of directional selection and the genetic variation present within a population?

A) Graph A
B) Graph B
C) Graph C
D) Graph D
E) Graph E

Question 6

Cystic fibrosis is a genetic disorder in homozygous recessive (ff) humans that typically significantly reduces life expectancy. Over time, we would expect the f allele frequency to ________ for this trait.

A) remain the same
B) increase
C) decrease
D) fluctuate

Question 7

For biologists studying a large flatworm population in the lab, which Hardy-Weinberg condition is most difficult to meet?

A) no selection
B) no genetic drift
C) no gene flow
D) no mutation
E) random mating

Question 8

Three-spined stickleback fish (Gasterosteus aculeatus) show substantial heritable variation in gill-raker length related to differences in their diets. Longer gill rakers appear to function better for capturing open-water prey, while shorter gill rakers function better for capturing shallow-water prey. Which of the following types of selection is most likely to be found in a large lake (open water in the middle and shallow water around the sides) with a high density of these fish?

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

Question 9

The recessive allele that causes sickle cell anemia is harmful to homozygous individuals. What maintains the presence of this allele in a population's gene pool?

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

Question 10

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

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

Question 11

A researcher wants to know if gene flow is contributing to evolution of drought tolerance of pitcher plants in a specific bog. As a control, she should

A) determine if the population is in Hardy-Weinberg equilibrium.
B) transplant pitcher plants from other populations into the bog.
C) estimate the frequency of alleles at relevant genes for drought tolerance.
D) All of the above steps should be taken.
E) None of these steps should be taken; gene flow does not contribute to evolution.

Question 12

Why doesn't inbreeding depression, by itself, cause evolution?

A) It decreases the population's average fitness.
B) It limits gene flow.
C) It does not change the population's allele frequencies.
D) It increases homozygosity.
E) It violates the Hardy-Weinberg assumptions.

Question 13

When nonrandom mating occurs in a population so that individuals prefer to mate with similar individuals, allele frequencies should

A) remain the same, but homozygotes will be overrepresented in the population.
B) remain the same, but heterozygotes will be overrepresented in the population.
C) change and heterozygotes will be overrepresented in the population.
D) change and homozygotes will be overrepresented in the population.
E) remain the same, at Hardy-Weinberg equilibrium.

Question 14

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 15

Use the following information to answer the question(s) below.
Martin Wikelski and L. Michael Romero (Body size, performance, and fitness in Galápagos marine iguanas, Integrative and Comparative Biology 43 [2003]: 376-86) measured the snout-to-vent (anus) length of Galápagos marine iguanas and observed the percent survival of different-sized animals, all of the same age. The graph shows the log snout-vent length (SVL, a measure of overall body size) plotted against the percent survival of these different-size classes for males and females.
Currently, the only predators of Galápagos marine iguanas are Galápagos hawks. Iguana body size is not correlated with risk of hawk predation, although small iguanas can sprint faster than large iguanas. If predators (for example, cats) that preferentially catch and eat slower iguanas are introduced to the island, iguana body size is likely to ________ in the absence of other factors; the iguanas would then be under ________ selection.

A) increase; directional
B) increase; disruptive
C) decrease; directional
D) decrease; disruptive
E) stay the same; stabilizing

Question 16

Use the following information to answer the question below.
Researchers studying a small milkweed population note that some plants produce a toxin and other plants do not. They identify the gene responsible for toxin production. The dominant allele (T) codes for an enzyme that makes the toxin, and the recessive allele (t) codes for a nonfunctional enzyme that cannot produce the toxin. Heterozygotes produce an intermediate amount of toxin. The genotypes of all individuals in the population are determined (see chart) and used to determine the actual allele frequencies in the population.
Refer to the accompanying figure. Is this population in Hardy-Weinberg equilibrium?

A) Yes.
B) No; there are more heterozygotes than expected.
C) No; there are more homozygotes than expected.
D) It is impossible to tell.

Question 17

Use the following information to answer the question(s) below.
Martin Wikelski and L. Michael Romero (Body size, performance, and fitness in Galápagos marine iguanas, Integrative and Comparative Biology 43 [2003]: 376-86) measured the snout-to-vent (anus) length of Galápagos marine iguanas and observed the percent survival of different-sized animals, all of the same age. The graph shows the log snout-vent length (SVL, a measure of overall body size) plotted against the percent survival of these different-size classes for males and females.
Examine the accompanying figure. What type of selection for body size appears to be occurring in these marine iguanas?

A) directional selection
B) stabilizing selection
C) disruptive selection
D) You cannot determine the type of selection from the above information.

Question 18

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

A) Evolution by natural selection represents the result of selection for acquired characteristics.
B) Evolution by natural selection is the production of adaptations that meet present and anticipated needs.
C) Evolution by natural selection is the descent of humans from the present-day great apes.
D) Evolution by natural selection is the differential survival and reproduction of the most-fit phenotypes.

Question 19

Suppose 64 percent of a remote mountain village can taste phenylthiocarbamide (PTC) and must, therefore, have at least one copy of the dominant PTC taster allele. If this population conforms to Hardy-Weinberg expectations for this gene, what percentage of the population must be heterozygous for this trait?

A) 16 percent
B) 32 percent
C) 40 percent
D) 48 percent
E) 60 percent

Question 20

Evolution in a population of island iguanas can be caused by the following agent(s):

A) natural selection.
B) genetic drift.
C) gene flow.
D) All of the above can be agents.
E) both natural selection and genetic drift.

Question 21

Genetic variation ________.

A) is created by the direct action of natural selection
B) arises in response to changes in the environment
C) must be present in a population before natural selection can act upon the population
D) tends to be reduced by when diploid organisms produce gametes

Question 22

Which of the following is the most predictable outcome of increased gene flow between two populations?

A) lower average fitness in both populations
B) higher average fitness in both populations
C) increased genetic difference between the two populations
D) decreased genetic difference between the two populations
E) increased genetic drift

Question 23

An earthquake decimates a ground-squirrel population, killing 98 percent of the squirrels. The surviving population happens to have broader stripes, on average, than the initial population. If broadness of stripes is genetically determined, what effect has the ground-squirrel population experienced during the earthquake?

A) directional selection
B) disruptive selection
C) a founder event
D) a genetic bottleneck
E) gene flow

Question 24

Natural selection ________.

A) is a random process
B) creates beneficial mutations
C) completely eliminates harmful mutations
D) can favor beneficial mutations

Question 25

Mutation is the only evolutionary mechanism that ________.

A) is the ultimate source of variation in natural populations
B) does little to change allele frequencies
C) decreases fitness
D) is more important in eukaryotes than in prokaryotes
E) has no effect on genetic variation

Question 26

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

Question 27

Use the following information to answer the question below.
In 1983, a population of dark-eyed junco birds became established on the campus of the University of California, San Diego (UCSD), which is located many miles from the junco's normal habitat in the mixed-coniferous temperate forests in the mountains. Juncos have white outer tail feathers that the males display during aggressive interactions and during courtship displays. Males with more white in their tail are more likely to win aggressive interactions, and females prefer to mate with males with more white in their tails. Females have less white in their tails than do males and display it less often. (Pamela J. Yeh. 2004. Rapid evolution of a sexually selected trait following population establishment in a novel habitat. Evolution 58[1]:166-74.)
Refer to the paragraph on dark-eyed junco birds. The UCSD campus male junco population tails were, on average, 36 percent white, whereas the tails of males from nearby mountain populations averaged 40-45 percent white. If this observed trait difference were due to a difference in the original colonizing population, it would most likely be due to ________.

A) mutations in the UCSD population
B) sexual selection
C) gene flow between populations
D) a genetic bottleneck
E) a founder effect

Question 28

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 29

When imbalances occur in the sex ratio of sexual species that have two sexes (that is, 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 30

Two frog populations (same species) living in two neighboring lakes sing slightly different courtship songs. Increased irrigation makes the land between the two lakes wetter, allowing frogs to expand their ranges to the area between the lakes. Females in both populations prefer loud frogs to quieter frogs but do not distinguish between the two slightly different songs. Assuming that courtship song differences have a genetic basis, predict what will likely happen to the songs of the two frog populations.

A) The songs will become more similar to each other.
B) Males will become louder.
C) Disruptive selection will cause the songs to differentiate even more.
D) Genetic drift will cause the songs to differentiate even more.
E) You cannot predict a change in the courtship songs at the two lakes.

Question 31

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, 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 increase in frequency.

Question 32

Genetic drift occurs in a population. Which of the following statements might be TRUE?

A) Genetic drift increased the population's fitness.
B) Genetic drift decreased the population's fitness.
C) The population was relatively small.
D) The population experiences a decrease in genetic variation.
E) Any of these statements can be true.

Question 33

In a small population of alpine foxes, you observe increased ear length over a 10-year period. Can you conclude that increase in ear length is advantageous in this population?

A) Yes.
B) No.

Question 34

The Dunkers are a religious group that moved from Germany to Pennsylvania in the mid-1700s. They do not marry with members outside their own immediate community. Today, the Dunkers are genetically unique and differ in gene frequencies, at many loci, from all other populations, including those in their original homeland. Which of the following likely explains the genetic uniqueness of this population?

A) population bottleneck and Hardy-Weinberg equilibrium
B) heterozygote advantage and stabilizing selection
C) sexual selection and inbreeding depression
D) mutation and natural selection
E) founder effect, inbreeding, and genetic drift

Question 35

Soon after the island of Hawaii rose above the sea surface (somewhat less than 1 million years ago) and organisms colonized the island, the evolution of life on this new island should have been most strongly influenced by ________.

A) a genetic bottleneck
B) sexual selection
C) habitat differentiation
D) founder effects

Question 36

Pea aphids (Acyrthosiphon pisum) are the only animals able to synthesize their own carotenoid pigments, due to lateral gene transfer from the genome of a fungus to the genome of a recent ancestor of the pea aphids. The resulting red or green coloration alters the risk the aphids face from specific predators and parasites. Select the correct statement below.

A) The lateral transfer of genes for carotenoid synthesis had a deleterious effect on the aphid genome.
B) Natural selection favored the lateral transfer of genes for carotenoid synthesis from a fungus to an aphid.
C) The lateral transfer of genes for carotenoid synthesis from a fungus to an aphid is a form of mutation.
D) The lateral transfer of genes for carotenoid synthesis occurred to provide the aphids with protection from their predators and parasites.

Question 37

In 1986, a nuclear power accident in Chernobyl, USSR (now Ukraine), led to high radiation levels for miles surrounding the plant. The high levels of radiation caused elevated mutation rates in the surviving organisms, and evolutionary biologists have been studying rodent populations in the Chernobyl area ever since. Based on your understanding of evolutionary mechanisms, which of the following most likely occurred in the rodent populations following the accident?

A) Mutation caused major changes in rodent physiology over time.
B) Mutation led to increased genetic variation.
C) Mutation caused genetic drift and decreased fitness.
D) Mutation caused the fixation of new alleles.