Population Genetics and Essential Biology I Advanced Prep:
Master Evolutionary Mechanics & Hardy-Weinberg
Equilibrium Practice Questions
Subject: Population Genetics, Hardy-Weinberg Principles, and Essential Biology
I
Question 1: In a large, isolated population of Drosophila melanogaster, the frequency of a
recessive lethal allele is $q = 0.1$. If the population undergoes one generation of random mating,
what is the expected frequency of the lethal phenotype in the subsequent generation, assuming
no mutation, migration, or selection occurring between birth and the phenotypic observation?
A) 0.01
B) 0.09
C) 0.18
D) 0.81
Correct Answer: A) 0.01
Explanation: According to the Hardy-Weinberg principle, the genotype frequencies in the next
generation are predicted by $p^2 + 2pq + q^2 = 1$. The frequency of the homozygous recessive
phenotype is represented by $q^2$. Given $q = 0.1$, $q^2 = (0.1)^2 = 0.01$. Distractors B and
C represent intermediate steps or incorrect applications of the $2pq$ heterozygous calculation,
and D represents the homozygous dominant frequency ($p^2$).
Question 2: Which condition must be strictly violated for a population to undergo evolutionary
change via genetic drift?
A) The population must be infinitely large.
B) Mating must be non-random.
C) Mutation rates must be non-zero.
D) Migration must occur between subpopulations.
Correct Answer: A) The population must be infinitely large.
Explanation: Genetic drift is defined as random fluctuations in allele frequencies due to
sampling error, which is inversely proportional to population size. An infinitely large population
,eliminates sampling error, thereby preventing genetic drift. While B, C, and D are factors in
evolution, they are not the prerequisite for the absence of drift.
Question 3: A population exhibits an excess of heterozygotes compared to Hardy-Weinberg
expectations. Which of the following is the most parsimonious explanation?
A) Inbreeding depression.
B) Disassortative mating.
C) Bottleneck effect.
D) Founder effect.
Correct Answer: B) Disassortative mating.
Explanation: Disassortative mating (negative assortative mating) occurs when individuals prefer
mates with phenotypes different from their own, which increases heterozygosity. Inbreeding (A),
bottlenecks (C), and founder effects (D) generally result in an excess of homozygotes.
Question 4: In a specific locus, the fitness values for genotypes AA, Aa, and aa are $w_{AA} =
0.8$, $w_{Aa} = 1.0$, and $w_{aa} = 0.6$. What will be the long-term outcome of natural
selection at this locus?
A) The allele 'a' will be fixed.
B) The allele 'A' will be fixed.
C) A stable polymorphism will be maintained.
D) Both alleles will be lost due to purging of deleterious mutations.
Correct Answer: C) A stable polymorphism will be maintained.
Explanation: This scenario describes heterozygote advantage (overdominance), where the fitness
of the heterozygote is greater than either homozygote. Selection acts to maintain both alleles in
the population at equilibrium, preventing the fixation of either A or a.
Question 5: How does the "Effective Population Size" ($N_e$) typically compare to the "Census
Population Size" ($N$) in natural populations?
A) $N_e$ is usually equal to $N$.
B) $N_e$ is usually smaller than $N$ due to factors like unequal sex ratios and variance in
reproductive success.
,C) $N_e$ is usually larger than $N$ because non-breeding individuals still contribute to the gene
pool.
D) $N_e$ is irrelevant in populations that have reached Hardy-Weinberg equilibrium.
Correct Answer: B) $N_e$ is usually smaller than $N$ due to factors like unequal sex ratios
and variance in reproductive success.
Explanation: The effective population size measures the genetic strength of a population; it is
almost always lower than the census size because only a fraction of the census population
contributes to the next generation's gene pool equally.
Question 6: According to the Neutral Theory of Molecular Evolution, most evolutionary changes
at the molecular level are caused by:
A) Genetic drift of selectively neutral alleles.
B) Natural selection favoring advantageous mutations.
C) High rates of spontaneous mutation.
D) Horizontal gene transfer.
Correct Answer: A) Genetic drift of selectively neutral alleles.
Explanation: Motoo Kimura’s Neutral Theory posits that the vast majority of evolutionary
changes at the DNA level are the result of random genetic drift of mutant alleles that are
selectively neutral, rather than direct selective pressure.
Question 7: A population of 100 individuals has an allele frequency of $p = 0.5$. If the
population experiences a severe bottleneck, reducing it to 10 individuals, what is the immediate
effect on the gene pool?
A) Allele frequencies are guaranteed to remain 0.5.
B) The probability of losing rare alleles increases significantly.
C) Genetic diversity increases due to increased mutation rate.
D) Hardy-Weinberg equilibrium is reached more rapidly.
Correct Answer: B) The probability of losing rare alleles increases significantly.
Explanation: Bottlenecks involve drastic reductions in population size. By sampling a very small
group from a large population, the probability of "missing" rare alleles is high, leading to a
permanent loss of genetic variation.
, Question 8: In a population where selection against a recessive lethal allele ($s = 1.0$) is
occurring, why is the allele never completely eliminated?
A) Mutation constantly regenerates the allele.
B) The allele is hidden in the heterozygous state where it is not exposed to selection.
C) Genetic drift favors the lethal allele in small populations.
D) The allele provides a slight fitness advantage in different environments.
Correct Answer: B) The allele is hidden in the heterozygous state where it is not exposed to
selection.
Explanation: Selection acts on phenotypes. In heterozygotes (Aa), the recessive lethal allele is
masked by the dominant allele. Because the phenotype is not expressed, the lethal allele is
protected from natural selection.
Question 9: Which of the following is an example of frequency-dependent selection?
A) The fitness of a genotype increases as its frequency in the population decreases.
B) The fitness of a genotype is constant regardless of its frequency.
C) Homozygotes are always favored over heterozygotes.
D) Sexual selection acts independently of allele frequency.
Correct Answer: A) The fitness of a genotype increases as its frequency in the population
decreases.
Explanation: Negative frequency-dependent selection, such as rare-male advantage or predator-
prey dynamics, grants higher fitness to rare phenotypes, thereby maintaining variation.
Question 10: In the context of the Hardy-Weinberg model, what is the expected frequency of
heterozygotes when the allele frequencies are $p=0.7$ and $q=0.3$?
A) 0.21
B) 0.42
C) 0.49
D) 0.09
Correct Answer: B) 0.42
Master Evolutionary Mechanics & Hardy-Weinberg
Equilibrium Practice Questions
Subject: Population Genetics, Hardy-Weinberg Principles, and Essential Biology
I
Question 1: In a large, isolated population of Drosophila melanogaster, the frequency of a
recessive lethal allele is $q = 0.1$. If the population undergoes one generation of random mating,
what is the expected frequency of the lethal phenotype in the subsequent generation, assuming
no mutation, migration, or selection occurring between birth and the phenotypic observation?
A) 0.01
B) 0.09
C) 0.18
D) 0.81
Correct Answer: A) 0.01
Explanation: According to the Hardy-Weinberg principle, the genotype frequencies in the next
generation are predicted by $p^2 + 2pq + q^2 = 1$. The frequency of the homozygous recessive
phenotype is represented by $q^2$. Given $q = 0.1$, $q^2 = (0.1)^2 = 0.01$. Distractors B and
C represent intermediate steps or incorrect applications of the $2pq$ heterozygous calculation,
and D represents the homozygous dominant frequency ($p^2$).
Question 2: Which condition must be strictly violated for a population to undergo evolutionary
change via genetic drift?
A) The population must be infinitely large.
B) Mating must be non-random.
C) Mutation rates must be non-zero.
D) Migration must occur between subpopulations.
Correct Answer: A) The population must be infinitely large.
Explanation: Genetic drift is defined as random fluctuations in allele frequencies due to
sampling error, which is inversely proportional to population size. An infinitely large population
,eliminates sampling error, thereby preventing genetic drift. While B, C, and D are factors in
evolution, they are not the prerequisite for the absence of drift.
Question 3: A population exhibits an excess of heterozygotes compared to Hardy-Weinberg
expectations. Which of the following is the most parsimonious explanation?
A) Inbreeding depression.
B) Disassortative mating.
C) Bottleneck effect.
D) Founder effect.
Correct Answer: B) Disassortative mating.
Explanation: Disassortative mating (negative assortative mating) occurs when individuals prefer
mates with phenotypes different from their own, which increases heterozygosity. Inbreeding (A),
bottlenecks (C), and founder effects (D) generally result in an excess of homozygotes.
Question 4: In a specific locus, the fitness values for genotypes AA, Aa, and aa are $w_{AA} =
0.8$, $w_{Aa} = 1.0$, and $w_{aa} = 0.6$. What will be the long-term outcome of natural
selection at this locus?
A) The allele 'a' will be fixed.
B) The allele 'A' will be fixed.
C) A stable polymorphism will be maintained.
D) Both alleles will be lost due to purging of deleterious mutations.
Correct Answer: C) A stable polymorphism will be maintained.
Explanation: This scenario describes heterozygote advantage (overdominance), where the fitness
of the heterozygote is greater than either homozygote. Selection acts to maintain both alleles in
the population at equilibrium, preventing the fixation of either A or a.
Question 5: How does the "Effective Population Size" ($N_e$) typically compare to the "Census
Population Size" ($N$) in natural populations?
A) $N_e$ is usually equal to $N$.
B) $N_e$ is usually smaller than $N$ due to factors like unequal sex ratios and variance in
reproductive success.
,C) $N_e$ is usually larger than $N$ because non-breeding individuals still contribute to the gene
pool.
D) $N_e$ is irrelevant in populations that have reached Hardy-Weinberg equilibrium.
Correct Answer: B) $N_e$ is usually smaller than $N$ due to factors like unequal sex ratios
and variance in reproductive success.
Explanation: The effective population size measures the genetic strength of a population; it is
almost always lower than the census size because only a fraction of the census population
contributes to the next generation's gene pool equally.
Question 6: According to the Neutral Theory of Molecular Evolution, most evolutionary changes
at the molecular level are caused by:
A) Genetic drift of selectively neutral alleles.
B) Natural selection favoring advantageous mutations.
C) High rates of spontaneous mutation.
D) Horizontal gene transfer.
Correct Answer: A) Genetic drift of selectively neutral alleles.
Explanation: Motoo Kimura’s Neutral Theory posits that the vast majority of evolutionary
changes at the DNA level are the result of random genetic drift of mutant alleles that are
selectively neutral, rather than direct selective pressure.
Question 7: A population of 100 individuals has an allele frequency of $p = 0.5$. If the
population experiences a severe bottleneck, reducing it to 10 individuals, what is the immediate
effect on the gene pool?
A) Allele frequencies are guaranteed to remain 0.5.
B) The probability of losing rare alleles increases significantly.
C) Genetic diversity increases due to increased mutation rate.
D) Hardy-Weinberg equilibrium is reached more rapidly.
Correct Answer: B) The probability of losing rare alleles increases significantly.
Explanation: Bottlenecks involve drastic reductions in population size. By sampling a very small
group from a large population, the probability of "missing" rare alleles is high, leading to a
permanent loss of genetic variation.
, Question 8: In a population where selection against a recessive lethal allele ($s = 1.0$) is
occurring, why is the allele never completely eliminated?
A) Mutation constantly regenerates the allele.
B) The allele is hidden in the heterozygous state where it is not exposed to selection.
C) Genetic drift favors the lethal allele in small populations.
D) The allele provides a slight fitness advantage in different environments.
Correct Answer: B) The allele is hidden in the heterozygous state where it is not exposed to
selection.
Explanation: Selection acts on phenotypes. In heterozygotes (Aa), the recessive lethal allele is
masked by the dominant allele. Because the phenotype is not expressed, the lethal allele is
protected from natural selection.
Question 9: Which of the following is an example of frequency-dependent selection?
A) The fitness of a genotype increases as its frequency in the population decreases.
B) The fitness of a genotype is constant regardless of its frequency.
C) Homozygotes are always favored over heterozygotes.
D) Sexual selection acts independently of allele frequency.
Correct Answer: A) The fitness of a genotype increases as its frequency in the population
decreases.
Explanation: Negative frequency-dependent selection, such as rare-male advantage or predator-
prey dynamics, grants higher fitness to rare phenotypes, thereby maintaining variation.
Question 10: In the context of the Hardy-Weinberg model, what is the expected frequency of
heterozygotes when the allele frequencies are $p=0.7$ and $q=0.3$?
A) 0.21
B) 0.42
C) 0.49
D) 0.09
Correct Answer: B) 0.42
