Question 1

Which chemical mutagen causes the deamination of adenine, resulting in a transition mutation from A/T to G/C?

Accepted Answer

Nitrous acid (HNO$$_2)$$

Question 2

A researcher exposes bacterial DNA to ethidium bromide. What type of mutation is most likely to result from this treatment?

Accepted Answer

Frameshift mutation

Question 3

Which DNA repair mechanism uses the enzyme photolyase and energy from visible light to directly reverse UV-induced thymine dimers?

Accepted Answer

Photoreactive repair

Question 4

A mutation in the phr gene of E. coli would most directly affect which DNA repair process?

Accepted Answer

Photoreactive repair

Question 5

Which of the following best describes the mechanism of action of alkylating agents such as EMS on DNA?

Accepted Answer

They add alkyl groups to guanine, causing G/C to A/T transitions.

Question 6

Which repair system is primarily responsible for removing small, non-helix-distorting base lesions from the genome?

Accepted Answer

Base excision repair (BER)

Question 7

A patient is exposed to strong X-rays, resulting in double-strand DNA breaks. Which repair mechanism is most likely to introduce mutations during repair?

Accepted Answer

Nonhomologous end joining (NHEJ)

Question 8

In the Ames test, a significant increase in revertant colonies on experimental plates compared to control plates indicates what?

Accepted Answer

The chemical tested is a potential mutagen.

Question 9

Which of the following is TRUE regarding nucleotide excision repair (NER)?

Accepted Answer

NER removes a short segment containing DNA damage and replaces it by DNA synthesis.

Question 10

A mutation in the MutH gene of E. coli would most likely impair which process?

Accepted Answer

Recognition of methylation on the original DNA strand during mismatch repair

Question 11

Which equation best represents the transition mutation caused by deamination of cytosine?

Accepted Answer

$$\mathrm{C/G} \rightarrow \mathrm{T/A}$$

Question 12

Which of the following statements about transposable elements is CORRECT?

Accepted Answer

Transposable elements can cause insertional inactivation, leading to nonfunctional gene products.

Question 13

Which repair mechanism is most accurate for repairing double-strand DNA breaks, and why?

Accepted Answer

Homologous recombination (HR), because it uses a homologous DNA template for repair.

Question 14

Which of the following is a real-world example of a phenotype caused by transposable element insertion?

Accepted Answer

Round versus wrinkled pea seeds

Question 15

Retrotransposons differ from DNA transposons in that retrotransposons:

Accepted Answer

Transpose via an RNA intermediate and reverse transcriptase.

Question 16

Which of the following is a plausible consequence of a defect in the BRCA1 gene?

Accepted Answer

Impaired signaling of DNA damage and increased cancer susceptibility

Question 17

Which of the following best explains why NHEJ is considered error-prone compared to HR?

Accepted Answer

NHEJ trims and ligates DNA ends without using a template, often resulting in mutations.

Question 18

Which of the following elements is most abundant in the human genome and can cause mutations by insertion?

Accepted Answer

LINEs (Long Interspersed Nuclear Elements)

Question 19

A scientist observes a DNA segment with flanking direct repeats and an internal region that can excise and insert elsewhere. What is this most likely to be?

Accepted Answer

A DNA transposon

Question 20

Which of the following mechanisms is NOT a way that genomes can change over evolutionary time?

Accepted Answer

Base excision repair

DNA Mutation and Repair Mechanisms: Chemical Mutagens, Intercalating Agents, and DNA Damage

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