Q: Which equation best represents the process of reverse transcription used by retrotransposons?

$$\text{RNA} \xrightarrow{\text{reverse transcriptase}} \text{cDNA}$$

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 homologous recombination. What is its primary function?

Accepted Answer

To allow the invading strand to pair with homologous DNA and displace one strand.

Question 5

Which pathway of homologous recombination repair always results in a non-crossover outcome?

Accepted Answer

Synthesis-dependent strand annealing (SDSA)

Question 6

Transposable elements can cause mutations by inserting into genes. Which scenario below is most likely to result in a frameshift mutation?

Accepted Answer

A transposable element inserts into the coding region of a gene.

Question 7

Which structural feature is required for a DNA transposon to be recognized and excised by transposase?

Accepted Answer

Inverted terminal repeats (ITRs)

Question 8

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

Accepted Answer

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

Question 9

LINE-1 (L1) elements are responsible for some human genetic diseases. Which of the following best explains how a LINE-1 insertion can cause hemophilia?

Accepted Answer

LINE-1 inserts into the F8 gene, disrupting its function and causing a mutant allele.

Question 10

Which equation best represents the process of reverse transcription used by retrotransposons?

Accepted Answer

$$	ext{RNA} \xrightarrow{	ext{reverse transcriptase}} 	ext{cDNA}$$

Question 11

Which of the following is a non-autonomous retrotransposon in the human genome?

Accepted Answer

Alu element

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 outcome when two identical transposable elements are present in a genome?

Accepted Answer

They can facilitate recombination, leading to duplications, deletions, or chromosomal rearrangements.

Question 14

In the Sleeping Beauty transposon system used to generate transgenic mice, what is the role of the transposase enzyme?

Accepted Answer

It excises and inserts the transposon into the genome.

Question 15

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

Accepted Answer

LINEs are autonomous and encode reverse transcriptase.

Question 16

A transposable element is inserted into the second intron of the white gene in Drosophila, causing a mutant phenotype. What is the most likely molecular consequence?

Accepted Answer

Premature termination of transcription and aberrant splicing of mRNA.

Question 17

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

Accepted Answer

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

Question 18

Which formula represents the creation of direct repeats (DRs) during DNA transposon insertion?

Accepted Answer

$$	ext{Target site} \xrightarrow{	ext{transposon insertion}} 	ext{DR} - 	ext{Transposon} - 	ext{DR}$$

Question 19

Which of the following is a key difference between LTR and non-LTR retrotransposons?

Accepted Answer

LTR retrotransposons contain long terminal repeats, while non-LTR retrotransposons do not.

Holliday Junctions, Homologous Recombination, and Transposable Elements

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