Medical Laboratory TechnicianĀ Exam Molecular Diagnostics 2 ā Questions and Answers
Question 1: FISH (Fluorescence In Situ Hybridization) is primarily used to detect:
- Bacterial contamination in blood cultures
- Chromosomal abnormalities and gene rearrangements (Correct answer)
- Viral load in serum
- Point mutations in mitochondrial DNA
Correct answer: Chromosomal abnormalities and gene rearrangements
FISH uses fluorescently labeled DNA probes that hybridize to specific chromosomal regions, allowing visualization of chromosomal abnormalities, deletions, duplications, and translocations.
Question 2: The BCR-ABL fusion gene detected by molecular methods is associated with which condition?
- Acute lymphoblastic leukemia only
- Chronic myelogenous leukemia (CML) (Correct answer)
- Multiple myeloma
- Hodgkin lymphoma
Correct answer: Chronic myelogenous leukemia (CML)
The BCR-ABL fusion gene results from the Philadelphia chromosome translocation t(9;22) and is the hallmark of CML, used for diagnosis and monitoring treatment response.
Question 3: DNA sequencing by the Sanger method uses which modified nucleotides to terminate chain elongation?
- Deoxyribonucleotides (dNTPs)
- Dideoxyribonucleotides (ddNTPs) (Correct answer)
- Ribonucleotides (rNTPs)
- Phosphorylated nucleotides
Correct answer: Dideoxyribonucleotides (ddNTPs)
Sanger sequencing incorporates dideoxynucleotides (ddNTPs), which lack a 3'-OH group, causing chain termination at specific bases, producing fragments of different lengths for sequence determination.
Question 4: Which quality control measure is most important in a molecular diagnostics laboratory to prevent false-positive results?
- Using heat-inactivated samples
- Strict physical separation of pre- and post-amplification areas (Correct answer)
- Running all samples in duplicate
- Using only fresh specimens
Correct answer: Strict physical separation of pre- and post-amplification areas
Physical separation of pre-amplification (specimen prep and PCR setup) from post-amplification (detection) areas prevents amplicon contamination, the primary cause of false-positive PCR results.
Question 5: What is a molecular beacon probe in real-time PCR?
- A linear probe that binds to the amplicon
- A hairpin-shaped probe with a fluorophore and quencher that fluoresces when hybridized (Correct answer)
- A radioactively labeled DNA probe
- A protein probe that binds DNA
Correct answer: A hairpin-shaped probe with a fluorophore and quencher that fluoresces when hybridized
Molecular beacons are hairpin-shaped oligonucleotides with a fluorophore at one end and a quencher at the other; when they hybridize to their target, the hairpin opens and fluorescence is emitted.
Question 6: Next-generation sequencing (NGS) differs from Sanger sequencing primarily in that NGS:
- Can only sequence short fragments of DNA
- Sequences millions of DNA fragments simultaneously in a massively parallel manner (Correct answer)
- Requires more sample volume than Sanger
- Is less accurate than Sanger sequencing
Correct answer: Sequences millions of DNA fragments simultaneously in a massively parallel manner
NGS platforms sequence millions of DNA fragments simultaneously through massively parallel processing, enabling whole-genome or whole-exome analysis at far greater throughput than Sanger sequencing.
Question 7: A positive internal control in a PCR assay serves to:
- Confirm the target sequence is absent
- Verify that PCR inhibitors in the specimen did not prevent amplification (Correct answer)
- Indicate sample contamination
- Determine the melting temperature of the amplicon
Correct answer: Verify that PCR inhibitors in the specimen did not prevent amplification
An internal control (co-amplified with the target) confirms that the PCR reaction worked properly; if the internal control fails to amplify, it suggests inhibitors in the specimen caused a false-negative result.
Medical Laboratory TechnicianĀ Exam Molecular Diagnostics 2
FISH (Fluorescence In Situ Hybridization) is primarily used to detect: