Q: Which of the following equations best represents the formation of a heteroduplex DNA region during homologous recombination?

$\text{ssDNA}_{A} + \text{dsDNA}_{B} \rightarrow \text{Heteroduplex}_{AB}$

Question 1

Which DNA repair mechanism is most likely to result in the loss of genetic information between direct repeats, and is associated with diseases such as non-insulin dependent diabetes and Fabry disease?

Accepted Answer

Single-strand annealing (SSA)

Question 2

In the context of double-strand break (DSB) repair, what is the primary function of the RecA protein in bacteria?

Accepted Answer

It polymerizes around single-stranded DNA to form nucleofilaments and promotes strand invasion.

Question 3

Which of the following best describes a Holliday junction?

Accepted Answer

A four-stranded DNA structure formed during homologous recombination.

Question 4

A mutation in which type of gene is most likely to result in a dramatically increased mutation rate and predisposition to cancer?

Accepted Answer

A DNA repair gene

Question 5

Which of the following is a consequence of depurination in DNA?

Accepted Answer

Loss of an adenine or guanine base, resulting in an abasic site

Question 6

During homologous recombination, which enzyme in eukaryotes is functionally analogous to RecA in bacteria?

Accepted Answer

Rad51

Question 7

Which repair pathway is most likely to correct a thymine dimer caused by ultraviolet irradiation?

Accepted Answer

Nucleotide excision repair

Question 8

A patient with a defect in the MRN complex is likely to have problems with which stage of double-strand break repair?

Accepted Answer

End processing and generation of 3' overhangs

Question 9

Which of the following equations best represents the formation of a heteroduplex DNA region during homologous recombination?

Accepted Answer

$	ext{ssDNA}_{A} + 	ext{dsDNA}_{B} ightarrow 	ext{Heteroduplex}_{AB}$

Question 10

Site-specific recombination is characterized by which of the following features?

Accepted Answer

It occurs at short, specific DNA sequences recognized by recombinase enzymes.

Question 11

Which of the following is a likely outcome if a cell is defective in both ruv and rec genes after exposure to UV irradiation?

Accepted Answer

The cell will accumulate DNA double-strand breaks and may die.

Question 12

Which of the following best explains the role of branch migration in homologous recombination?

Accepted Answer

It moves the crossover point along the DNA, increasing the length of heteroduplex DNA.

Question 13

A mutation that converts cytosine to uracil in DNA is most likely to be corrected by which repair pathway?

Accepted Answer

Base excision repair

Question 14

Which of the following is a direct consequence of a mismatch repair defect in a human cell?

Accepted Answer

Accumulation of replication errors and increased mutation rate

Question 15

Which protein complex is responsible for holding double-strand breaks together and preparing them for resection in eukaryotic cells?

Accepted Answer

MRN complex (Mre11-Rad50-Nbs1)

Question 16

Which of the following scenarios is most likely to result in gene conversion?

Accepted Answer

DSB repair with mismatch repair in heteroduplex DNA

Question 17

Which equation best represents the process of DNA strand invasion during homologous recombination?

Accepted Answer

$	ext{ssDNA}_{A} + 	ext{dsDNA}_{B} \xrightarrow{RecA/Rad51} 	ext{D-loop}$

Question 18

Which of the following is a real-world example of a mutation that can lead to cancer due to defective DNA repair?

Accepted Answer

Mutation in the BRCA1 gene leading to impaired homologous recombination

Question 19

Which repair system is most likely to be triggered by a bulky DNA adduct caused by exposure to polycyclic aromatic hydrocarbons from cigarette smoke or BBQ?

Accepted Answer

Nucleotide excision repair

DNA Recombination II: Mechanisms and Biological Implications

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