Question 1

Which of the following best explains why RNA viruses have higher mutation rates compared to DNA viruses?

Accepted Answer

RNA-dependent RNA polymerases lack proofreading activity, leading to frequent replication errors.

Question 2

A mutation changes a codon from UAU (tyrosine) to UAA (stop codon). What type of mutation is this?

Accepted Answer

Nonsense mutation

Question 3

Which equation best represents the average mutation rate per nucleotide per year in a typical eukaryotic genome?

Accepted Answer

$$1 	imes 10$$^{-9}$$

Question 4

A frameshift mutation occurs when:

Accepted Answer

A nucleotide is inserted or deleted, altering the reading frame

Question 5

Which of the following is a transition mutation?

Accepted Answer

G changes to A

Question 6

A patient with Huntington disease has 60 CAG repeats in the HTT gene. Based on the table of trinucleotide repeat disorders, what is the most likely principal phenotype?

Accepted Answer

Uncontrolled movement

Question 7

Which repair mechanism is primarily responsible for correcting deaminated cytosine in DNA?

Accepted Answer

Base excision repair (BER)

Question 8

A chemical mutagen causes the conversion of cytosine to uracil. What is the most likely outcome during DNA replication?

Accepted Answer

A C to T transition

Question 9

Which of the following best describes the mechanism of action of ethidium bromide as a mutagen?

Accepted Answer

It intercalates between DNA base pairs, causing frameshift mutations.

Question 10

A mutation in the promoter region of a gene most likely results in:

Accepted Answer

Altered levels of gene expression

Question 11

Which of the following is TRUE regarding somatic mutations?

Accepted Answer

They can cause cancer in the affected tissue but are not passed to offspring.

Question 12

Which repair pathway is most active throughout the cell cycle and is used for double-strand break repair in both dividing and non-dividing cells?

Accepted Answer

Non-homologous end joining (NHEJ)

Question 13

A patient is exposed to aflatoxin B1, which is metabolized in the liver to a mutagenic epoxide. Which test would best confirm the mutagenicity of this compound?

Accepted Answer

Ames test using S9 extract

Question 14

Which protein is activated in response to high levels of DNA damage and can induce cell cycle arrest or apoptosis?

Accepted Answer

p53

Question 15

During homologous recombination in meiosis, what is the function of the Holliday junction?

Accepted Answer

It allows for the exchange of genetic material between homologous chromosomes.

Question 16

A mutation changes a codon from GAA (glutamic acid) to GAG (glutamic acid). What type of mutation is this?

Accepted Answer

Silent (synonymous) mutation

Question 17

Which of the following is a plausible outcome of a suppressor mutation?

Accepted Answer

Restoration of wild-type phenotype despite the presence of the original mutation

Question 18

Which of the following best describes the mechanism of strand slippage during DNA replication?

Accepted Answer

Temporary detachment and reattachment of DNA polymerase leads to hairpin formation and repeat expansion.

Question 19

Which of the following is a consequence of the deamination of 5-methylcytosine?

Accepted Answer

Formation of thymine

Question 20

Which repair mechanism is used by E. coli to correct mismatched base pairs after DNA replication, and how does it distinguish the correct strand?

Accepted Answer

Mismatch repair; by methylation of the original strand

Mutation, DNA Repair, and Homologous Recombination

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