AP Biology : 7.4 Population Genetics – Exam Style questions with Answer- MCQ

Question

In which populations is genetic drift more likely to occur?
(A) large populations
(B) small populations
(C) populations with great diversity
(D) populations with a high degree of gene flow

▶️Answer/Explanation

Ans:

(B) Genetic drift, the random loss of alleles, is more likely in small
populations because in small populations, fewer individuals would
have the opportunity to pass on a rare allele to the next generation than
in a large population. Choice (A) is incorrect because it is the opposite
of the correct answer. Greater diversity does not influence the chances
of genetic drift, so choice (C) is incorrect. Choice (D) is incorrect
because gene flow, or migration, does not necessarily cause genetic
drift.

Question

A group of birds is flying south during their yearly migration when a hurricane with extremely strong winds occurs. Only 10% of the group
survive the storm, reaching their winter nesting site and reproducing the next spring. This type of event is an example of
(A) the bottleneck effect because only the fittest members of the
population survived.
(B) the bottleneck effect because the population size was rapidly
reduced.
(C) the founder effect because the group of birds from before the
storm were not genetically diverse.
(D) the founder effect because the birds colonized a new habitat and
never migrated again back to their original habitat.

▶️Answer/Explanation

Ans:

(B) The bottleneck effect occurs when the majority of a population dies
and the surviving individuals do not possess all of the alleles from the
original population. Choice (A) is incorrect because survival after
bottleneck events may be random and is not dependent on an
organism’s fitness. The founder effect occurs when a small group of
individuals leaves a larger population to colonize a new area. Since this
scenario does not describe the founder effect, choices (C) and (D) are
incorrect. Also, nothing in the question provides any information on the
genetic diversity of the population before the hurricane, which further
rules out choice (C). Choice (D) can be further ruled out because
nothing in the question suggests that the birds never migrated back to
their original habitat.

Question

Which of the following best explains the conditions under which the founder effect occurs?
(A) Random evolutionary change happens over multiple generations,
causing a large population to separate into two smaller,
genetically different populations.
(B) A population’s size is rapidly reduced, and the genetic diversity of
the surviving population is not representative of the original,
larger population.
(C) A small group of individuals from a larger population colonizes a
new habitat. The small group that colonizes the new habitat does
not possess the genetic diversity of the original, larger population.
(D) Environmental pressures select for the individuals with the
adaptations that give them a greater likelihood of surviving and
reproducing.

▶️Answer/Explanation

Ans:

(C) The founder effect occurs when a small group of individuals from
a large population leaves the larger group to colonize a new area and
the small group does not possess the same allele frequencies as the
larger group. Choice (A) is incorrect because the founder effect is not
caused by random evolutionary change. The rapid reduction of a
population’s size, leading to a group of survivors that is not
representative of the original, larger population, is the bottleneck effect.
Thus, choice (B) is incorrect. Choice (D) is incorrect because it
describes the process of natural selection, not the founder effect.

Question

An isolated population in the United States are descendants of approximately 200 immigrants who arrived in the 1700s. Some individuals in this group of immigrants carried the allele for Ellis-Van Creveld syndrome. Today, this allele occurs at a much higher frequency in the descendants of this group than in the general population in the United States. This difference in the frequency of the Ellis-Van Creveld allele is an example of
(A) the bottleneck effect.
(B) the founder effect.
(C) natural selection.
(D) random mutations over multiple generations.

▶️Answer/Explanation

Ans:

(B) This scenario is an example of the founder effect. Choice (A) is
incorrect because the original population did not undergo a rapid
decrease in population size. There is no evidence in the question that
Ellis-Van Creveld syndrome leads to decreased survival, so choice (C)
is incorrect. Choice (D) is incorrect because it would be extremely
unlikely that random mutations over several generations would lead to
the appearance of the allele that causes Ellis-Van Creveld syndrome.

Question

A scientist is studying the allele frequencies for a particular gene in a population of wild prairie dogs over a five-year period. The allele
frequencies are shown in the table.

YearFrequency of Allele A1Frequency of Allele A2
10.001.00
20.001.00
30.100.90
40.130.87
50.150.85

Which of the following is the most likely cause of the observed change in allele frequencies?
(A) artificial selection
(B) natural selection
(C) genetic drift
(D) gene flow

▶️Answer/Explanation

Ans:

(D) Initially, the population of wild prairie dogs did not possess the A1
allele, so it is likely that it arrived in an individual prairie dog that
migrated into the population sometime between years 2 and 3.
Therefore, gene flow is the correct answer. Choice (A) is incorrect
because these are wild prairie dogs, and there is no evidence of
selective breeding of prairie dogs by humans. No information is given
in the question about whether or not alleles A1 or A2 confer a survival
advantage, so choice (B) is incorrect. No allele was lost in the
population, so choice (C) is incorrect.

Scroll to Top