Question 1

Which of the following best describes a missense mutation?

Accepted Answer

A mutation that changes one amino acid in the protein sequence.

Question 2

A patient is diagnosed with a hereditary disease caused by an increase in the number of trinucleotide repeats in a gene. Which type of mutation is most likely responsible?

Accepted Answer

Nucleotide repeat expansion

Question 3

Which of the following mutations is most likely to result in a nonfunctional protein due to a shift in the reading frame?

Accepted Answer

Frameshift mutation

Question 4

A mutation changes a codon from $$\mathrm{UAC} ($$tyrosine) to $$\mathrm{UAA} ($$stop). What type of mutation has occurred?

Accepted Answer

Nonsense mutation

Question 5

Which DNA repair mechanism is most likely to introduce additional errors when repairing double-strand breaks?

Accepted Answer

Non-homologous end joining (NHEJ)

Question 6

A base analog such as 5-bromouridine can cause mutations because:

Accepted Answer

It pairs with normal nucleotides but can mispair, leading to base substitutions.

Question 7

Which of the following best explains why mutations in non-coding regions can cause disease?

Accepted Answer

They can alter gene regulation, leading to over- or under-expression of a gene.

Question 8

A mutation in the promoter region of a gene reduces the level of transcription. What type of mutation is this?

Accepted Answer

Regulatory mutation

Question 9

Which of the following is a consequence of a cryptic splice site mutation?

Accepted Answer

Additional nucleotides are retained in the mature mRNA, potentially altering the protein sequence.

Question 10

Which chemical mutagen is most likely to cause frameshift mutations by distorting the DNA duplex?

Accepted Answer

Intercalating agents

Question 11

A DNA sequence undergoes a transition mutation. Which of the following best describes this event?

Accepted Answer

A purine is replaced by another purine, or a pyrimidine by another pyrimidine.

Question 12

Which of the following best describes a forward mutation?

Accepted Answer

A mutation that converts a wild-type allele to a mutant allele.

Question 13

A patient is exposed to UV irradiation, resulting in the formation of thymine dimers. Which DNA repair mechanism is most likely to fix this damage?

Accepted Answer

Nucleotide excision repair

Question 14

Which of the following is a spontaneous mutation mechanism that can occur during DNA replication?

Accepted Answer

Strand slippage leading to repeat expansion

Question 15

A mutation in the splice site of an intron leads to retention of the intron in the mature mRNA. What is the most likely consequence?

Accepted Answer

Reduced production of functional protein due to splicing errors

Question 16

Which of the following best describes the proofreading capability of DNA polymerase?

Accepted Answer

It removes incorrectly paired nucleotides during DNA replication.

Question 17

A mutagen causes the loss of an amino group from cytosine, converting it to uracil. What type of chemical change has occurred?

Accepted Answer

Deamination

Question 18

Which of the following equations correctly represents the mutation rate per base pair in most organisms at the DNA level?

Accepted Answer

$$10^{-9}$$

Question 19

A second mutation elsewhere in the genome compensates for the effect of a first mutation, restoring the wild-type phenotype. What is this phenomenon called?

Accepted Answer

Second-site reversion (suppressor mutation)

Question 20

Which of the following is NOT a possible consequence of a transposon insertion?

Accepted Answer

Increase in DNA polymerase proofreading accuracy

Mutations and Genome Changes: Mechanisms, Types, and Consequences

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