Question 1

In a population of beetles, a specific allele

A

provides resistance to a newly introduced pesticide. Scientists observe that the frequency of allele

A

increases from

0.15

to

0.55

over five generations. Which of the following is the most likely interpretation of this change in allele frequency?

Accepted Answer

The pesticide acted as a selective pressure, increasing the fitness of individuals carrying the

A

allele.

Answer

The population is in Hardy-Weinberg equilibrium, and the change is due to random mating.

Answer

The population underwent genetic drift, which randomly increased the frequency of the

A

allele.

Answer

The mutation rate of the gene increased significantly due to the presence of the pesticide.

Question 2

A small group of 15 birds is blown off course during a storm and establishes a new population on an isolated island. The original mainland population had an allele frequency of

A

for a particular neutral trait, but the new island population has an allele frequency of

A

for that same trait. Which process best explains this change?

Accepted Answer

The founder effect, a form of genetic drift, caused a non-representative sample of alleles to start the new population.

Answer

Directional selection favored the allele that increased to

A

due to better adaptation to island life.

Answer

The increase in frequency occurred because the population reached Hardy-Weinberg equilibrium immediately.

Answer

Gene flow between the island and the mainland increased the frequency of the common allele.

Question 3

In a large, isolated population of wildflowers, the frequency of a recessive allele

A

for white petal color changes from

A

to

0.15

over several generations. During this time, no significant environmental changes occurred. What is the most likely interpretation of this data?

Accepted Answer

The population is likely stable and approximating Hardy-Weinberg equilibrium, as the change in allele frequency is negligible.

Answer

The white petal trait is being selected against because the frequency of the

A

allele decreased.

Answer

Strong disruptive selection is occurring, favoring both homozygous dominant and homozygous recessive phenotypes.

Answer

The population is experiencing a bottleneck effect, leading to a rapid loss of genetic diversity.

Question 4

In a population of mice habitat, a volcanic eruption occurs, leaving large areas of dark basalt rock. Over several years, biological surveys show the frequency of a dark-fur allele

A

increases from

A

to

0.15

, while the light-fur allele

0.55

decreases. If the population size remains very large throughout this period, which of the following is the most valid conclusion regarding the change in allele frequencies?

Accepted Answer

The change is primarily driven by natural selection because the dark-fur phenotype provides a survival advantage in the new environment.

Answer

The change is primarily driven by the bottleneck effect, as the volcanic eruption must have killed a random subset of the population.

Answer

The change is primarily driven by a high rate of spontaneous mutations from allele

A

to allele

A

.

Answer

The change is primarily driven by genetic drift because the population size is high enough to allow for random fluctuations.

Question 5

Suppose a population of insects is monitored for a locus with two alleles,

A

and

A

. Initially, the frequency of

0.15

is

0.55

. After a sudden environmental change, the frequency of

B

remains

0.5

, but the frequency of the heterozygous genotype

Bb

drops significantly below

2pq

. Which of the following is the most likely interpretation of this change?

Accepted Answer

Disruptive selection is occurring, where both homozygous phenotypes have higher fitness than the intermediate phenotype.

Answer

Stabilizing selection is occurring, favoring the heterozygous individuals over both homozygotes.

Answer

The population is experiencing the founder effect, which naturally reduces the number of heterozygotes over time.

Answer

Directional selection is occurring, causing the

A

allele to become fixed in the population.

Question 6

In a specific population of fish, an allele

A

for small size has a frequency of

A

, and an allele

0.15

for large size has a frequency of

0.55

. After a local drought reduces the water level, making larger fish more visible to avian predators, the frequency of

B

increases to

0.5

within two generations. How should this change in allele frequency be interpreted?

Accepted Answer

Directional selection occurred because the environmental change created a fitness advantage for the small-sized phenotype.

Answer

Genetic drift occurred because the drought randomly removed individuals regardless of their size phenotype.

Answer

Gene flow occurred because small fish from a neighboring pond migrated to escape the drought conditions.

Answer

Stabilizing selection occurred because the extreme phenotypes were eliminated, maintaining the average size.

Question 7

A biologist studies a population of plants where the frequency of a homozygous recessive genotype (white flowers) is

A

. After a specific species of pollinator that prefers white flowers becomes extinct in the area, the frequency of the recessive allele

A

drops from

0.15

to

0.55

over several years. What is the most likely interpretation of this shift in allele frequency?

Accepted Answer

The fitness of the white-flowered phenotype decreased, leading to negative selection against the

A

allele.

Answer

The change is due to spontaneous mutations converting the recessive

A

allele into a dominant

A

allele at an accelerated rate.

Answer

Genetic drift occurred because the population size must have increased after the pollinator became extinct.

Answer

The population is experiencing stabilizing selection, which preserves the intermediate phenotype and increases the frequency of the

A

allele.

Question 8

An isolated population of 2,000 squirrels lives in a forest. A research study finds that the frequency of an allele

A

for a shortened tail is

A

. After a severe fire reduces the population to 25 individuals, the frequency of allele

0.15

is measured at

0.55

in the surviving group. Which of the following is the most accurate interpretation of this allele frequency change?

Accepted Answer

The change is due to a genetic bottleneck, where a random event drastically reduced the population size and altered allele frequencies by chance.

Answer

The change is due to directional selection, as squirrels with shorter tails were better adapted to survive the fire.

Answer

The change is due to gene flow, as new individuals with the

A

allele likely migrated into the forest after the fire.

Answer

The population is in Hardy-Weinberg equilibrium because the change in frequency ensures that

A

.

Question 9

In a population of tropical fish, the frequency of an allele

A

for bright coloration is

A

. After the introduction of a new predator that hunts by sight, the frequency of the

0.15

allele drops to

0.55

over three generations. Which of the following is the most appropriate interpretation of this data?

Accepted Answer

Directional selection has occurred because the bright coloration phenotype now has lower fitness due to increased predation.

Answer

Genetic drift has occurred because the predator randomly consumed individuals regardless of their color.

Answer

The mutation rate for the

A

allele increased to help the fish blend in with their environment.

Answer

The population is experiencing stabilizing selection, which favors the intermediate phenotype of medium brightness.

Question 10

In a population of flowering plants, a researcher monitors a locus with two alleles,

A

and

A

. Over ten generations, the frequency of

0.15

fluctuates randomly between

0.55

,

B

,

0.5

, and

Bb

, without a consistent upward or downward trend. The population size is relatively small (approx. 50 individuals). What is the most likely interpretation of these allele frequency changes?

Accepted Answer

The changes are primarily driven by genetic drift, which causes unpredictable fluctuations in small populations.

Answer

The population is undergoing directional selection, favoring the

A

allele over the

A

allele.

Answer

The population is experiencing strong gene flow from a much larger neighboring population.

Answer

The fluctuations are a result of a high mutation rate changing

A

to

A

and back again.

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