Question 1

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

Accepted Answer

Natural selection acts upon existing genetic variation in a population. Therefore, genetic variation must be present in a population before natural selection can act upon it.

Question 2

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

Accepted Answer

Increased gene flow between two populations results in increased gene exchange, leading to decreased genetic differences between the two populations. This is because gene flow introduces new alleles into each population, reducing the genetic divergence between them.

Question 3

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

Accepted Answer

The earthquake caused a drastic reduction in the ground-squirrel population, killing 98% of the squirrels. This led to a genetic bottleneck, in which the surviving population is likely not representative of the initial population in terms of genetic variation. The fact that the surviving population has, on average, broader stripes suggests that there may have been selection for this trait during the bottleneck, as individuals with broader stripes may have had a better chance of survival. However, without more information about the genetic basis of stripe broadness and the specific selective pressures at play, it is difficult to say for certain what type of selection (if any) was operating.

Question 4

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

Accepted Answer

Natural selection can favor beneficial mutations because organisms with beneficial mutations are more likely to survive and reproduce, passing those beneficial traits on to their offspring. It does not create mutations itself nor does it completely eliminate harmful mutations. While some harmful mutations may lead to decreased fitness and be eliminated by natural selection, others may not have a significant impact on survival and reproduction and may persist in a population.

Question 5

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

Accepted Answer

Mutation is the ultimate source of variation in natural populations. Other mechanisms, such as natural selection, genetic drift, and gene flow, operate on the variation created by mutation.

Question 6

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

Accepted Answer

Genetic drift is the random fluctuations in gene frequencies due to chance events such as founder effects, bottleneck events or simply random variations in reproductive success. Genetic drift is most pronounced in small populations where chance events can have a greater impact on gene frequency. In larger populations, genetic drift is less likely to occur as chance events are diluted in a larger pool. Therefore, genetic drift most consistently requires a small population as a precondition for its occurrence.

Question 7

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

Accepted Answer

The observed trait difference between the UCSD population and the nearby mountain populations is most likely due to a founder effect because the UCSD population was established from a small group of individuals that were not representative of the larger mountain population. This led to a reduced genetic variation in the UCSD population, which may have led to the observed lower average percentage of white in their tails.

Question 8

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 this scenario, directional selection would operate on the finch population because the only individuals that would survive and reproduce would be those with larger bills capable of cracking the now-hard seeds. The frequency of the "large-billed" genotype would increase while the "small-billed" genotype would decrease, leading to a shift in the population's genetic composition.

Question 9

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

Accepted Answer

This phenomenon is an example of frequency-dependent selection, where the fitness of a phenotype depends on its frequency relative to other phenotypes in a given population. In this case, the rarity of one sex makes it more valuable for reproductive success, leading to increased parental investment.

Question 10

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.

Accepted Answer

When the frogs from both populations expand their ranges to the area between the lakes, they will likely come into contact and mate with each other. As both populations prefer loud frogs, there will be selection for louder courtship songs. However, because females do not distinguish between the slightly different songs, there will be no selection for one specific song. As a result, the songs will likely become more similar to each other as the genes for loudness become more prevalent in the combined population.

Question 11

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.

Accepted Answer

If the Tamiflu-resistance gene involves a cost, it will experience directional selection leading to reduction in its frequency. This means that the gene will be selected against and will be eliminated from the population over time if it does not provide any significant advantage. This is because the cost of carrying the gene outweighs any potential benefits.

Question 12

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.

Accepted Answer

Genetic drift is a mechanism of evolution that can lead to random changes in the population's genetic makeup. It can increase or decrease a population's fitness, often occurs more significantly in small populations, and can lead to a decrease in genetic variation. Therefore, any of the statements A, B, C, or D could be true depending on the specific circumstances of the population experiencing genetic drift.

Question 13

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.

Accepted Answer

Observing an increase in a trait alone is not enough to conclude that it is advantageous. There could be other factors at play, such as genetic drift or mutations. Additionally, the fitness advantage of a trait can vary depending on environmental conditions and other factors. Therefore, further research is needed to determine whether the increase in ear length is advantageous or not.

Question 14

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

Accepted Answer

The genetic uniqueness of the Dunker population is likely due to the founder effect, inbreeding, and genetic drift. When a small group of individuals establishes a new population, such as when the Dunkers migrated to Pennsylvania, the genetic makeup of the founding population can have a disproportionate effect on the genetic diversity of the new population. Inbreeding within the small population can lead to further reductions in genetic diversity, and genetic drift can cause changes in gene frequencies due to random events rather than natural selection. All of these factors can contribute to the genetic uniqueness of the Dunker population.

Question 15

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

Accepted Answer

The answer of  Soon after the island of Hawaii...

Question 16

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.

Accepted Answer

Lateral gene transfer is a form of mutation as it involves the introduction of new genetic material into an organism's genome, which can lead to new traits.

Question 17

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.

Accepted Answer

The high radiation levels caused by the nuclear accident likely increased the mutation rate in rodent populations. As a result, the increased genetic variation may have allowed some individuals to survive and reproduce in the new environment. This can lead to "adaptive evolution", which is the process by which populations evolve in response to environmental changes. While mutations may cause changes in rodent physiology over time, it is more likely that the increased genetic variation led to increased abilities to adapt to the environment. Additionally, genetic drift and decreased fitness are possible outcomes of mutations, but there is no evidence to suggest that this occurred in the Chernobyl rodent populations. Finally, it is unlikely that new alleles became fixed in the population as a result of the accident since genetic variation would have been increased.

Quiz 23: Evolutionary Processes

Genetic variation ________.

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

Natural selection ________.

Mutation is the only evolutionary mechanism that ________.

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?

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?

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

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?

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 ________.