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📝 Mutations and natural selection evolution (11 MCQs)

📖 From Principles of Biochemistry • 1. The Foundations of Biochemistry • 11 questions available

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What is Mutations and natural selection evolution?

Definition:
Mutations are heritable changes in the DNA sequence that create genetic variation, and natural selection acts on this variation by favoring alleles that increase fitness, leading to changes in allele frequencies over generations, and this is the fundamental mechanism of evolution, resulting in adaptation and speciation, and it operates at the molecular level by altering protein sequences and regulatory regions.

Working:
Mutations work by altering the genetic code, which can change the amino acid sequence of proteins, affect expression levels, or create new functions; the mutation rate is typically $10^{-8}$ to $10^{-10}$ per base pair per generation in bacteria, and natural selection works by differential survival and reproduction, where the equation $\Delta p = \frac{p(1-p)(w_A - w_a)}{\bar{w}}$ describes the change in allele frequency, and beneficial mutations are selected and spread, while harmful ones are eliminated, driving evolutionary change and enabling adaptation to new environments.

Example:
A simple example is the mutation that confers resistance to the antibiotic rifampicin in bacteria, where a single nucleotide change in the RNA polymerase gene allows the bacteria to survive in the presence of the drug, and natural selection then increases the frequency of this allele in the population, illustrating how mutations and selection drive evolution.

Reason:
Understanding mutations and natural selection is fundamental to evolutionary biology, genetics, and medicine, as it explains the origin of diversity, the emergence of antibiotic resistance, and the development of diseases like cancer, and it is essential for conservation and biotechnology.

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📝 All Mutations and natural selection evolution MCQs

Q1. A population contains individuals with different inherited traits. Which sequence best explains how a new mutation can contribute to evolutionary change over several generations?

A.Mutation creates a heritable difference, environmental selection changes reproductive success, and allele frequencies shift ✅

B.Natural selection creates a useful mutation, which immediately becomes fixed in every individual

C.An individual's acquired trait is inherited and automatically increases the population's mutation rate

D.Mutation occurs only after environmental selection identifies the trait that the population needs

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: A mutation can introduce a heritable genetic difference before selection acts. If the resulting phenotype affects reproductive success, individuals carrying the advantageous variant may leave more offspring, causing the associated allele to become more common across generations.

Q2. Why can a mutation that has no obvious effect on an organism still be important for future evolution?

A.It always produces an immediate survival advantage

B.It can alter a hereditary sequence without changing the present phenotype, while potentially providing variation for future conditions ✅

C.It prevents natural selection from acting on the population

D.It guarantees that the organism will develop a new adaptation

💡 Difficulty: medium | ✅ Correct: B

📖 Explanation: A mutation may be neutral under current conditions, meaning its immediate phenotype or fitness effect is negligible. However, environmental conditions can change, and the same genetic variation may later influence survival or reproduction.

Q3. Two populations of the same organism experience different environments. Population X contains mostly allele A, while population Y contains mostly allele B. If A improves survival in X but B improves survival in Y, what is the strongest conclusion?

A.Natural selection should favor different alleles in the two environments ✅

B.Only allele A can be beneficial because it occurs in one population

C.Mutations cannot occur once natural selection begins

D.The population with allele B must eventually replace population X

💡 Difficulty: hard | ✅ Correct: A

📖 Explanation: Fitness is context-dependent. An allele that improves survival or reproduction in one environment may not provide the same advantage elsewhere. Therefore, natural selection can favor different hereditary variants in different environments.

Q4. A researcher claims, 'Because an organism needs a particular adaptation, its hereditary instructions will change specifically to produce that adaptation.' Which correction is most scientifically appropriate?

A.Mutations arise as directed responses whenever an organism needs them

B.Natural selection creates mutations by increasing the mutation rate of useful genes

C.Heritable variation can arise independently of immediate need, and selection can increase variants that improve reproductive success ✅

D.Adaptations occur only when every individual acquires the same mutation simultaneously

💡 Difficulty: hard | ✅ Correct: C

📖 Explanation: The claim confuses mutation with selection. Genetic changes can arise without being directed toward a future need. Natural selection then changes the frequency of variants according to their effects on survival and reproduction.

Q5. A population initially has allele frequencies $A=0.80$ and $a=0.20$ . After several generations in a changed environment, the frequencies become $A=0.35$ and $a=0.65$ . Which interpretation is most defensible?

A.The hereditary composition of the population changed, suggesting differential reproductive success or another evolutionary process ✅

B.Every individual with allele A must have mutated directly into allele a

C.The environment caused all individuals to intentionally change their genotype

D.The allele frequencies prove that mutation was the only mechanism responsible

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: Allele frequencies changing across generations indicates evolution at the population level. The change could result from natural selection, mutation, migration, drift, or combinations of processes, so the data alone do not establish one mechanism exclusively.

Q6. A bacterial population contains a rare mutation that makes some cells less affected by an antibiotic. Before treatment, the mutation is uncommon. After repeated antibiotic exposure, resistant cells become much more common. What best explains the observation?

A.The antibiotic caused every bacterial cell to develop the exact same useful mutation

B.Pre-existing or newly arising heritable variation allowed resistant cells to survive and reproduce more successfully ✅

C.The bacteria intentionally changed their DNA because they recognized the antibiotic

D.Natural selection eliminated the possibility of any further mutation

💡 Difficulty: medium | ✅ Correct: B

📖 Explanation: The antibiotic creates a selective environment rather than necessarily directing a specific mutation. Cells carrying heritable resistance can survive treatment more successfully and reproduce, increasing the frequency of resistance-associated variants.

Q7. A student observes that darker insects become more common on dark tree bark and concludes, 'The insects changed color because they wanted to hide better.' What is the main flaw in this reasoning?

A.It assumes that individuals intentionally modify hereditary instructions to satisfy environmental demands ✅

B.It assumes that mutations are always harmful

C.It ignores that insects have DNA

D.It assumes natural selection can operate only in laboratory populations

💡 Difficulty: easy | ✅ Correct: A

📖 Explanation: The reasoning treats adaptation as an intentional response by individuals. Evolutionary change generally results from heritable variation already present or arising through genetic change, followed by differences in survival or reproduction.

Q8. A graph records the percentage of individuals carrying a beneficial hereditary variant: Generation 1: 10%, Generation 2: 14%, Generation 3: 22%, Generation 4: 35%, Generation 5: 51%. Which conclusion is best supported by this trend?

A.The variant is becoming more common, consistent with positive selection or another evolutionary process favoring its carriers ✅

B.The variant must have appeared for the first time in Generation 5

C.The environment cannot influence the frequency of hereditary variants

D.The increase proves that every mutation is beneficial

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: The steadily increasing frequency shows that carriers of the variant became a larger proportion of the population. This pattern is consistent with selection favoring the variant, although the graph alone cannot prove the exact mechanism.

Q9. Two researchers propose explanations for an increase in a hereditary variant. Researcher 1 says the variant improves reproductive success in the current environment. Researcher 2 says individuals consciously changed their DNA because they needed the trait. Which explanation is more consistent with evolutionary reasoning?

A.Researcher 1, because differential reproductive success can change variant frequencies across generations ✅

B.Researcher 2, because organisms always control which mutations occur

C.Both explanations are equally supported by the observations

D.Neither explanation can involve hereditary variation

💡 Difficulty: easy | ✅ Correct: A

📖 Explanation: Evolutionary change can occur when inherited variants affect reproductive success, causing their frequencies to increase or decrease over generations. Conscious alteration of DNA to satisfy a need is not required for natural selection.

Q10. A population has two hereditary variants. Variant P provides a small reproductive advantage in Environment 1, while Variant Q provides a larger advantage in Environment 2. The environment switches from 1 to 2 after several generations. What prediction is most reasonable?

A.Q may increase in frequency after the environmental shift if its carriers reproduce more successfully ✅

B.P must remain dominant because natural selection cannot reverse direction

C.Both variants must immediately reach equal frequencies

D.The environmental shift eliminates all hereditary variation

💡 Difficulty: easy | ✅ Correct: A

📖 Explanation: Natural selection depends on environmental conditions and reproductive consequences. If Environment 2 gives Q carriers greater reproductive success, Q can increase in frequency, even if P was previously favored in Environment 1.

Q11. A researcher compares two populations after many generations. Population M shows little change in the frequency of a hereditary variant despite strong environmental differences, while Population N shows a rapid increase in the same variant under similar conditions. Which additional observation would most strongly help explain the difference?

A.Whether the variant has different effects on survival or reproduction in the two populations ✅

B.Whether both populations contain DNA

C.Whether the organisms have cells

D.Whether mutations are possible in principle

💡 Difficulty: hard | ✅ Correct: A

📖 Explanation: Different evolutionary outcomes can result from differences in selection pressure, genetic background, population size, migration, or other factors. Measuring the variant's actual effect on survival and reproduction directly tests whether selection differs between populations.

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