Question 1

Which of the following best describes the principle behind the Ames test for mutagenicity?

Accepted Answer

It detects the conversion of his- auxotrophs to his+ prototrophs after exposure to a potential mutagen.

Question 2

A patient is diagnosed with hereditary colon cancer. Which DNA repair pathway is most likely defective in this individual?

Accepted Answer

Mismatch repair

Question 3

Which of the following mutations is responsible for cystic fibrosis, as described in the study materials?

Accepted Answer

A three-base-pair deletion of phenylalanine codon at position 508 of the CFTR gene

Question 4

Which DNA repair mechanism is responsible for removing bulky lesions that distort the DNA double helix, such as thymine dimers?

Accepted Answer

Nucleotide excision repair

Question 5

A mutation in the polyadenylation site of the HBB gene most likely results in which of the following?

Accepted Answer

Unstable mRNAs due to reduced efficiency of mRNA cleavage and polyadenylation

Question 6

Which of the following statements about photoactivation repair is correct?

Accepted Answer

It is found in many organisms except humans and uses blue light to activate the photoreactivation enzyme.

Question 7

Which of the following best describes the mechanism of action for DNA transposons?

Accepted Answer

They use a cut-and-paste mechanism involving transposase and inverted terminal repeats (ITRs).

Question 8

A maize kernel displays pigmented spots due to the movement of a transposable element. Which genetic system is responsible for this phenomenon?

Accepted Answer

Ac-Ds system

Question 9

Which of the following is a key difference between autonomous and nonautonomous DNA transposons?

Accepted Answer

Autonomous elements encode the transposase enzyme required for their own movement.

Question 10

Which repair pathway is most likely to be activated in bacteria when there is extensive DNA damage that blocks replication, and what is a consequence of this pathway?

Accepted Answer

SOS repair; increased mutation rate due to error-prone DNA polymerases

Question 11

A patient with xeroderma pigmentosum is highly sensitive to sunlight and prone to skin cancer. Which DNA repair pathway is defective in this disorder?

Accepted Answer

Nucleotide excision repair

Question 12

Which of the following equations correctly represents the relationship between the number of revertant colonies in the Ames test and the mutagenicity of a compound?

Accepted Answer

$$N_{revertants} \propto [mutagen]$$

Question 13

Which of the following best describes the function of DNA glycosylase in base excision repair?

Accepted Answer

It removes the damaged base from DNA.

Question 14

Which of the following is a consequence of a single base-pair mutation in the TATA sequence at position -30 upstream of the HBB gene?

Accepted Answer

Decreased gene transcription and severe disease

Question 15

Which of the following statements about LINEs and SINEs in the human genome is correct?

Accepted Answer

They are examples of retrotransposons that move via an RNA intermediate.

Question 16

A mutation creates an abnormal mRNA splice site in the HBB gene. What is the most likely outcome?

Accepted Answer

Reduced or abolished mRNA splicing, leading to severe disease

Question 17

Which repair pathway is most likely to be defective in a patient with X-ray hypersensitivity and a predisposition to hereditary breast and ovarian cancers?

Accepted Answer

Double-strand break repair

Question 18

Which of the following best describes the difference between the mechanisms of DNA transposons and retrotransposons?

Accepted Answer

DNA transposons move via a cut-and-paste mechanism, while retrotransposons move via a copy-and-paste mechanism using an RNA intermediate.

Question 19

Which enzyme is responsible for recognizing inverted terminal repeats (ITRs) at the ends of DNA transposons?

Accepted Answer

Transposase

Question 20

Which of the following best explains why mutations in DNA repair genes are often associated with increased cancer susceptibility?

Accepted Answer

Defective DNA repair leads to accumulation of mutations, some of which may activate oncogenes or inactivate tumor suppressor genes.

DNA Repair and Transposition: Mechanisms and Implications in Genetics

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