$$\text{RNA} \xrightarrow{\text{Reverse Transcriptase}} \text{cDNA}$$

Question 1

Which of the following best describes the initial step in homologous recombination repair (HRR) of a double-strand break in DNA?

Accepted Answer

Both DNA strands are digested at the break site to create single-stranded overhangs.

Question 2

During the resolution of a Holliday junction, what determines whether the outcome is a crossover or non-crossover event?

Accepted Answer

The orientation of the cuts made by resolving enzymes at the junction.

Question 3

Which phase(s) of the cell cycle is homologous recombination repair (HRR) most likely to occur, and why?

Accepted Answer

S and G2 phases, because a sister chromatid is available as a template.

Question 4

A D-loop is formed during strand invasion in homologous recombination. What is the primary function of the D-loop?

Accepted Answer

To create a site for DNA polymerase to synthesize new DNA using the homologous template.

Question 5

Which of the following is a key structural feature of a DNA transposon?

Accepted Answer

Inverted Terminal Repeats (ITRs) flanking an open reading frame encoding transposase.

Question 6

What is the main difference between the mechanism of DNA transposons and retrotransposons?

Accepted Answer

DNA transposons move directly as DNA, while retrotransposons move via an RNA intermediate.

Question 7

LINE-1 (L1) elements are classified as which type of transposable element, and what is their significance in the human genome?

Accepted Answer

Non-LTR, autonomous retrotransposons; they encode reverse transcriptase and make up about 17% of the genome.

Question 8

A mutation in the F8 gene caused by a LINE-1 insertion results in hemophilia. Which of the following best explains how this mutation arose?

Accepted Answer

A de novo mutation occurred due to a retrotransposon (LINE-1) inserting into the F8 gene during gamete formation.

Question 9

Which of the following equations correctly represents the process of reverse transcription used by retrotransposons?

Accepted Answer

$$	ext{RNA} \xrightarrow{	ext{Reverse Transcriptase}} 	ext{cDNA}$$

Question 10

Which of the following best describes the outcome of the Synthesis-Dependent Strand Annealing (SDSA) pathway in homologous recombination repair?

Accepted Answer

Strand returns to original DNA, no stable junction formed, always non-crossover.

Question 11

Which of the following is a plausible consequence of transposable element insertion into the regulatory region of a gene?

Accepted Answer

The gene's expression may be disrupted, leading to altered phenotype.

Question 12

What is the evolutionary significance of transposable elements in shaping genomes?

Accepted Answer

They provide raw material for adaptation and can be beneficial if mutations are selected for.

Question 13

Which of the following best describes the mechanism of 'cut-and-paste' transposition?

Accepted Answer

Transposase excises the DNA transposon and reinserts it at a new site, creating direct repeats at the insertion site.

Question 14

Which of the following is true about SINEs (Short Interspersed Elements) in the human genome?

Accepted Answer

They are non-autonomous retrotransposons that use LINE machinery for transposition.

Question 15

Which of the following best explains how transposable elements can cause chromosomal rearrangements?

Accepted Answer

By providing identical sequences that facilitate recombination, leading to duplications, deletions, inversions, or translocations.

Question 16

In the context of genetic engineering, how can transposable elements be repurposed as tools?

Accepted Answer

By using transposase to randomly insert genes of interest into the genome, enabling identification of disease-related genes.

Question 17

Which of the following is a correct description of the structure of a simple transposon?

Accepted Answer

It contains a transposase gene, an antibiotic-resistance gene, and inverted repeats at both ends, flanked by direct repeats in the host genome.

Question 18

Which of the following best describes the process of cDNA library generation?

Accepted Answer

mRNA is converted to cDNA by reverse transcriptase, then cDNA is ligated into vectors and transformed into bacteria for amplification.

Homologous Recombination and Transposable Elements: Mechanisms and Genetic Impact

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