Diagnostic Genetic Sciences – Final Laboratory Practical
DGS 4235 – LAB IN MOLECULAR DIAGNOSTICS | FINAL LAB
PRACTICAL | EXAM QUESTIONS AND CORRECT ANSWERS |
2026/2027
DGS 4235 Final Lab Practical
1. A blood specimen for DNA extraction arrives in a lavender-top tube.
Which anticoagulant does this tube contain?
A. Sodium citrate
B. Potassium oxalate
C. Sodium heparin
D. EDTA
D. EDTA
EDTA chelates Mg2+, protecting DNA from nucleases, and does not inhibit
PCR the way heparin does.
2. Why is heparinized blood generally avoided for PCR-based molecular
testing?
A. Heparin degrades genomic DNA during storage
B. Heparin causes red cell lysis in transit
C. Heparin binds to agarose and distorts bands
D. Heparin inhibits Taq DNA polymerase
D. Heparin inhibits Taq DNA polymerase
Heparin co-purifies with nucleic acids and inhibits polymerase activity,
giving false negatives.
Page 1 of 51
, Diagnostic Genetic Sciences – Final Laboratory Practical
3. A student sets a P200 pipette to 250 µL. What is the most likely
consequence?
A. The tip will hold the extra 50 µL in reserve
B. The pipette automatically delivers 200 µL
C. Delivery will be accurate but slower
D. Damage to the pipette and inaccurate delivery
D. Damage to the pipette and inaccurate delivery
Setting a pipette beyond its rated range strains the piston mechanism and
gives unreliable volumes.
4. When aspirating with a standard air-displacement pipette, the
plunger should be pressed to which point?
A. Halfway between first and second stop
B. The second stop
C. The first stop
D. Past the second stop to the ejector
C. The first stop
The first stop sets the calibrated volume; the second stop is only used for
blow-out during dispensing.
5. Which pipetting technique is best suited for viscous solutions such as
glycerol-containing enzyme stocks?
A. Multi-dispensing from a single aspiration
B. Reverse pipetting
C. Forward pipetting with rapid release
D. Pre-wetting with water
B. Reverse pipetting
Reverse pipetting draws excess liquid and leaves the film in the tip,
improving accuracy with viscous reagents.
6. Ethidium bromide is handled with nitrile gloves primarily because it
is a:
A. Mutagen that intercalates DNA
B. Radioactive emitter
C. Volatile neurotoxin
D. Strong corrosive acid
A. Mutagen that intercalates DNA
EtBr inserts between base pairs and is a recognised mutagen, so skin
contact must be avoided.
Page 2 of 51
, Diagnostic Genetic Sciences – Final Laboratory Practical
7. Which UV wavelength range does a standard gel documentation
transilluminator emit, requiring face protection?
A. Visible blue light (about 470 nm)
B. Infrared (above 700 nm)
C. Far UV below 100 nm
D. Short to mid UV (about 254–312 nm)
D. Short to mid UV (about 254–312 nm)
Transilluminators emit damaging UV; a face shield protects the eyes and
skin from burns.
8. Formamide used in FISH denaturation solutions is a hazard because
it is a:
A. Strong oxidiser
B. Radioactive isotope
C. Teratogen
D. Pyrophoric solid
C. Teratogen
Formamide is a reproductive toxin and must be handled in a fume hood
with gloves.
9. To reduce PCR contamination, which workflow is correct?
A. Reagent prep, then sample prep, then amplification, then product
analysis in separate areas
B. Amplification first, then reagent prep in the same hood
C. Sample prep after gel analysis in the post-PCR room
D. Product analysis and reagent prep at the same bench
A. Reagent prep, then sample prep, then amplification, then product
analysis in separate areas
A unidirectional workflow keeps amplicons from re-entering clean pre-
PCR spaces.
10. Aerosol-barrier (filter) tips are used in molecular work mainly to:
A. Prevent aerosols from contaminating the pipette shaft
B. Increase the volume a tip can hold
C. Make tips autoclavable
D. Speed up aspiration
A. Prevent aerosols from contaminating the pipette shaft
Filters block droplets and aerosols that could carry template between
samples.
Page 3 of 51
, Diagnostic Genetic Sciences – Final Laboratory Practical
11. What is the purpose of a 10% bleach wipe-down of the PCR bench
before setup?
A. Oxidise and fragment contaminating DNA
B. Sterilise bacteria only
C. Remove RNase but not DNA
D. Neutralise ethidium bromide
A. Oxidise and fragment contaminating DNA
Sodium hypochlorite damages nucleic acids, destroying stray templates
and amplicons.
12. The class II biological safety cabinet is used for cell culture because
it provides:
A. Protection for the user, the product and the environment
B. A completely sealed glove-box barrier
C. Protection for the product only
D. Protection for the user only
A. Protection for the user, the product and the environment
Class II cabinets use HEPA-filtered inflow and downflow air to protect all
three.
13. Samples for RNA analysis should ideally be stored at:
A. −20 °C in a frost-free freezer
B. 4 °C
C. Room temperature
D. −80 °C
D. −80 °C
RNA is labile; ultra-low temperature limits RNase activity and hydrolysis.
14. A frost-free −20 °C freezer is poorly suited to enzyme storage
because:
A. It lacks shelving for tubes
B. It cycles temperature during defrost
C. It exposes enzymes to UV light
D. It cannot reach below −10 °C
B. It cycles temperature during defrost
Periodic warming during defrost cycles can damage enzymes and
reagents.
Page 4 of 51
DGS 4235 – LAB IN MOLECULAR DIAGNOSTICS | FINAL LAB
PRACTICAL | EXAM QUESTIONS AND CORRECT ANSWERS |
2026/2027
DGS 4235 Final Lab Practical
1. A blood specimen for DNA extraction arrives in a lavender-top tube.
Which anticoagulant does this tube contain?
A. Sodium citrate
B. Potassium oxalate
C. Sodium heparin
D. EDTA
D. EDTA
EDTA chelates Mg2+, protecting DNA from nucleases, and does not inhibit
PCR the way heparin does.
2. Why is heparinized blood generally avoided for PCR-based molecular
testing?
A. Heparin degrades genomic DNA during storage
B. Heparin causes red cell lysis in transit
C. Heparin binds to agarose and distorts bands
D. Heparin inhibits Taq DNA polymerase
D. Heparin inhibits Taq DNA polymerase
Heparin co-purifies with nucleic acids and inhibits polymerase activity,
giving false negatives.
Page 1 of 51
, Diagnostic Genetic Sciences – Final Laboratory Practical
3. A student sets a P200 pipette to 250 µL. What is the most likely
consequence?
A. The tip will hold the extra 50 µL in reserve
B. The pipette automatically delivers 200 µL
C. Delivery will be accurate but slower
D. Damage to the pipette and inaccurate delivery
D. Damage to the pipette and inaccurate delivery
Setting a pipette beyond its rated range strains the piston mechanism and
gives unreliable volumes.
4. When aspirating with a standard air-displacement pipette, the
plunger should be pressed to which point?
A. Halfway between first and second stop
B. The second stop
C. The first stop
D. Past the second stop to the ejector
C. The first stop
The first stop sets the calibrated volume; the second stop is only used for
blow-out during dispensing.
5. Which pipetting technique is best suited for viscous solutions such as
glycerol-containing enzyme stocks?
A. Multi-dispensing from a single aspiration
B. Reverse pipetting
C. Forward pipetting with rapid release
D. Pre-wetting with water
B. Reverse pipetting
Reverse pipetting draws excess liquid and leaves the film in the tip,
improving accuracy with viscous reagents.
6. Ethidium bromide is handled with nitrile gloves primarily because it
is a:
A. Mutagen that intercalates DNA
B. Radioactive emitter
C. Volatile neurotoxin
D. Strong corrosive acid
A. Mutagen that intercalates DNA
EtBr inserts between base pairs and is a recognised mutagen, so skin
contact must be avoided.
Page 2 of 51
, Diagnostic Genetic Sciences – Final Laboratory Practical
7. Which UV wavelength range does a standard gel documentation
transilluminator emit, requiring face protection?
A. Visible blue light (about 470 nm)
B. Infrared (above 700 nm)
C. Far UV below 100 nm
D. Short to mid UV (about 254–312 nm)
D. Short to mid UV (about 254–312 nm)
Transilluminators emit damaging UV; a face shield protects the eyes and
skin from burns.
8. Formamide used in FISH denaturation solutions is a hazard because
it is a:
A. Strong oxidiser
B. Radioactive isotope
C. Teratogen
D. Pyrophoric solid
C. Teratogen
Formamide is a reproductive toxin and must be handled in a fume hood
with gloves.
9. To reduce PCR contamination, which workflow is correct?
A. Reagent prep, then sample prep, then amplification, then product
analysis in separate areas
B. Amplification first, then reagent prep in the same hood
C. Sample prep after gel analysis in the post-PCR room
D. Product analysis and reagent prep at the same bench
A. Reagent prep, then sample prep, then amplification, then product
analysis in separate areas
A unidirectional workflow keeps amplicons from re-entering clean pre-
PCR spaces.
10. Aerosol-barrier (filter) tips are used in molecular work mainly to:
A. Prevent aerosols from contaminating the pipette shaft
B. Increase the volume a tip can hold
C. Make tips autoclavable
D. Speed up aspiration
A. Prevent aerosols from contaminating the pipette shaft
Filters block droplets and aerosols that could carry template between
samples.
Page 3 of 51
, Diagnostic Genetic Sciences – Final Laboratory Practical
11. What is the purpose of a 10% bleach wipe-down of the PCR bench
before setup?
A. Oxidise and fragment contaminating DNA
B. Sterilise bacteria only
C. Remove RNase but not DNA
D. Neutralise ethidium bromide
A. Oxidise and fragment contaminating DNA
Sodium hypochlorite damages nucleic acids, destroying stray templates
and amplicons.
12. The class II biological safety cabinet is used for cell culture because
it provides:
A. Protection for the user, the product and the environment
B. A completely sealed glove-box barrier
C. Protection for the product only
D. Protection for the user only
A. Protection for the user, the product and the environment
Class II cabinets use HEPA-filtered inflow and downflow air to protect all
three.
13. Samples for RNA analysis should ideally be stored at:
A. −20 °C in a frost-free freezer
B. 4 °C
C. Room temperature
D. −80 °C
D. −80 °C
RNA is labile; ultra-low temperature limits RNase activity and hydrolysis.
14. A frost-free −20 °C freezer is poorly suited to enzyme storage
because:
A. It lacks shelving for tubes
B. It cycles temperature during defrost
C. It exposes enzymes to UV light
D. It cannot reach below −10 °C
B. It cycles temperature during defrost
Periodic warming during defrost cycles can damage enzymes and
reagents.
Page 4 of 51
