Question 1

Which DNA repair pathway is primarily responsible for correcting small, non-helix-distorting base lesions such as deaminated cytosine in human cells?

Accepted Answer

Base Excision Repair (BER)

Question 2

A patient with xeroderma pigmentosum is highly sensitive to sunlight and develops skin cancers at a young age. Which DNA repair pathway is defective in this disorder?

Accepted Answer

Nucleotide Excision Repair (NER)

Question 3

In bacteria, how does the mismatch repair system distinguish the newly synthesized DNA strand from the template strand?

Accepted Answer

By the absence of methylation on the new strand

Question 4

Which enzyme is responsible for recognizing and removing damaged bases in the base excision repair pathway?

Accepted Answer

DNA glycosylase

Question 5

A double-strand break in DNA is repaired using a sister chromatid as a template, resulting in error-free repair. Which pathway is this?

Accepted Answer

Homologous Recombination (HR)

Question 6

Which of the following statements about nonhomologous end joining (NHEJ) is correct?

Accepted Answer

NHEJ can result in loss of nucleotides at the repair site.

Question 7

Which of the following is NOT a function of the MutS protein in bacterial mismatch repair?

Accepted Answer

Making a nick in the DNA strand

Question 8

A researcher exposes E. coli to UV light, causing thymine dimers to form. Which repair mechanism can directly reverse this damage using blue light?

Accepted Answer

Photoreactivation repair

Question 9

Which of the following is a key difference between direct repair and base excision repair?

Accepted Answer

Direct repair restores the original base structure without removing nucleotides.

Question 10

A double-strand break occurs in a human cell during G1 phase. Which repair pathway is most likely to be used, and what is a possible consequence?

Accepted Answer

Nonhomologous end joining; possible loss of genetic information

Question 11

Which of the following is NOT necessary for homologous recombination to occur?

Accepted Answer

5′ DNA strand overhangs

Question 12

If two genes are located far apart on the same chromosome, what is the maximum recombination frequency that can be observed between them?

Accepted Answer

$$50\%$$

Question 13

Which of the following best explains why sexual reproduction via meiosis increases genetic variation among offspring?

Accepted Answer

It increases genetic variation through independent assortment, crossing over, and random fertilization.

Question 14

A fruit fly geneticist observes that the recombination frequency between two genes is $$10\%. $$What is the distance between these genes in map units (centiMorgans)?

Accepted Answer

$$10 cM$$

Question 15

Which of the following statements about thymine dimers is NOT accurate?

Accepted Answer

Thymine dimers are covalent links between thymidines on opposite DNA strands.

Question 16

Which process is responsible for generating genetic diversity by swapping segments of parental chromosomes during meiosis?

Accepted Answer

Crossing over

Question 17

Which protein acts as a scaffold, binding to broken DNA ends and recruiting other proteins during nonhomologous end joining (NHEJ)?

Accepted Answer

Ku proteins

Question 18

A geneticist finds that the recombination frequency between yellow and white genes in Drosophila is $$0.5\%$$, and between white and miniature is $$34.5\%. $$Which two genes are physically closest together?

Accepted Answer

Yellow and white

Question 19

Which of the following is NOT a difference between mitosis and meiosis?

Accepted Answer

Meiosis results in genetically identical daughter cells.

DNA Mutation, Repair, and Genetic Mapping in Eukaryotes

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