ASCP Technologist in Molecular Biology (MB) Certification Exam — Questions and Answers

Question 1: Running the same sample on different days, by different operators, primarily assesses which performance characteristic?

Repeatability
Linearity
Reproducibility (intermediate precision) (Correct answer)
Analytical specificity

Correct answer: Reproducibility (intermediate precision)

Variation across days and operators assesses intermediate precision/reproducibility rather than within-run repeatability.

Question 2: Which PCR application is used to detect chromosomal translocations such as BCR-ABL fusion in chronic myeloid leukemia (CML)?

Methylation-specific PCR
Reverse transcription PCR targeting the fusion transcript (Correct answer)
Standard genomic DNA PCR
LAMP amplification

Correct answer: Reverse transcription PCR targeting the fusion transcript

RT-PCR targets the BCR-ABL mRNA fusion transcript produced by the Philadelphia chromosome translocation, providing a highly sensitive diagnostic and monitoring tool for CML.

Question 3: Before choosing reference genes for a new tissue and treatment, what is the best practice?

Use GAPDH because it is always stable
Use 18S rRNA only
Normalize to total plate fluorescence
Validate candidate genes for stability under the study conditions (Correct answer)

Correct answer: Validate candidate genes for stability under the study conditions

Reference gene stability varies by tissue and treatment and must be empirically validated, e.g., with geNorm or NormFinder.

Question 4: Why is fluorometric quantification (e.g., dye-based dsDNA assays) often preferred over UV absorbance for low-concentration samples?

It detects all nucleotides, including free dNTPs
It is more sensitive and specific for dsDNA, unaffected by RNA or free nucleotides (Correct answer)
It requires no standards
It measures protein contamination simultaneously

Correct answer: It is more sensitive and specific for dsDNA, unaffected by RNA or free nucleotides

Fluorescent dyes bind specifically to dsDNA, giving accurate low-level quantification without interference from RNA or nucleotides.

Question 5: Which PCR-based method is used to quantify viral load in HIV-positive patients to monitor antiretroviral therapy effectiveness?

Digital droplet PCR only
Nested PCR
Colony PCR
Quantitative RT-PCR (Correct answer)

Correct answer: Quantitative RT-PCR

Quantitative RT-PCR measures HIV RNA copies per milliliter of plasma, providing clinicians with data to monitor viral suppression during treatment.

Question 6: What consequence can result from failing to maintain proper regulatory standards & compliance standards in Polymerase Chain Reaction?

Loss of certification, legal penalties, and reputational damage (Correct answer)
Increased customer satisfaction
Reduced workload for staff
Lower training requirements

Correct answer: Loss of certification, legal penalties, and reputational damage

Non-compliance can result in serious consequences including certification revocation, legal penalties, fines, and significant reputational damage.

Question 7: Which application of digital PCR (dPCR) gives it an advantage over qPCR for rare mutation detection in liquid biopsy samples?

Faster thermal cycling speed
Absolute quantification without a standard curve (Correct answer)
Larger sample volume capacity
Lower reagent costs

Correct answer: Absolute quantification without a standard curve

dPCR partitions the reaction into thousands of droplets, allowing absolute quantification of rare mutations without relying on a standard curve, increasing sensitivity for liquid biopsy.

Question 8: On a Levey-Jennings chart, a single control value falls outside ±3 SD of the mean. Which Westgard rule is violated?

2-2s
1-3s (Correct answer)
10x
R-4s

Correct answer: 1-3s

The 1-3s rule rejects a run when one control value exceeds the mean ±3 SD, usually pointing to random error.

Question 9: In a qPCR run, Sample A has a Ct of 22 and Sample B has a Ct of 28 for the same target. What does this indicate?

Sample A was contaminated with primer dimers
Both samples had equal starting template
Sample A had more starting template than Sample B (Correct answer)
Sample B had more starting template than Sample A

Correct answer: Sample A had more starting template than Sample B

Ct is inversely related to starting template quantity, so a lower Ct means more initial target.

Question 10: Using the 2^-ΔΔCt method, a treated sample has a ΔΔCt of -2 relative to the control. What is the fold change in expression?

2-fold increase
4-fold decrease
0.25-fold change
4-fold increase (Correct answer)

Correct answer: 4-fold increase

2^-(-2) = 2^2 = 4, so expression is up 4-fold.

Question 11: The MIQE guidelines primarily address which aspect of PCR?

Biosafety level requirements
Laboratory staffing ratios
Thermal cycler calibration intervals
Minimum information for publishing and reporting qPCR experiments (Correct answer)

Correct answer: Minimum information for publishing and reporting qPCR experiments

MIQE (Minimum Information for Publication of Quantitative Real-Time PCR Experiments) standardizes qPCR reporting for transparency and reproducibility.

Question 12: What is the PRIMARY objective of specimen collection & handling within the Polymerase Chain Reaction profession?

To ensure quality outcomes through standardized practices and continuous improvement (Correct answer)
To limit the scope of professional activities
To maintain the status quo without change
To create additional requirements for practitioners

Correct answer: To ensure quality outcomes through standardized practices and continuous improvement

The primary objective is ensuring quality outcomes through established standards while continuously improving practices and processes.

Question 13: When choosing locations for environmental swab monitoring, which site has the highest priority?

Exterior building walls
Break room refrigerators
High-touch surfaces like pipettes, centrifuge lids, and hood work surfaces (Correct answer)
Ceiling tiles in office areas

Correct answer: High-touch surfaces like pipettes, centrifuge lids, and hood work surfaces

High-touch surfaces in the work areas are where contamination most likely builds up and spreads into reactions.

Question 14: In forensic DNA analysis in the US, which PCR-based technique is used to generate a DNA profile for identity comparison?

STR (Short Tandem Repeat) PCR analysis (Correct answer)
Multiplex ligation-dependent probe amplification
Digital PCR
Restriction fragment length polymorphism

Correct answer: STR (Short Tandem Repeat) PCR analysis

STR PCR analysis amplifies multiple short tandem repeat loci simultaneously to generate a DNA profile used by CODIS for identity matching.

Question 15: How is the limit of detection (LOD) of a qPCR assay commonly defined?

The Ct value of the NTC
The concentration that gives a Ct of 40
The highest concentration on the standard curve
The lowest concentration detected in at least 95% of replicates (Correct answer)

Correct answer: The lowest concentration detected in at least 95% of replicates

LOD is usually the lowest target level that is reliably detected, typically in 95% of replicates.

Question 16: In real-time qPCR, what does the cycle threshold (Ct) represent?

The cycle at which fluorescence crosses a set threshold above background (Correct answer)
The total number of cycles run
The melting temperature of the product
The cycle at which the reaction reaches plateau

Correct answer: The cycle at which fluorescence crosses a set threshold above background

Ct is the cycle where signal first rises detectably above background, and it is inversely related to starting template amount.

Question 17: Why should denaturation steps not be made much longer than needed?

Long high-temperature exposure reduces polymerase activity and can depurinate the template (Correct answer)
It makes primers bind more specifically
It raises the dNTP concentration
It shortens the amplicon

Correct answer: Long high-temperature exposure reduces polymerase activity and can depurinate the template

Extended time at 94-98°C shortens enzyme half-life and damages DNA through depurination.

Question 18: Which PCR application is most commonly used in US clinical laboratories to detect SARS-CoV-2?

RT-PCR (reverse transcription PCR) (Correct answer)
Allele-specific PCR
Inverse PCR
Standard endpoint PCR

Correct answer: RT-PCR (reverse transcription PCR)

RT-PCR is used to detect SARS-CoV-2 because the virus has an RNA genome that must first be reverse-transcribed into cDNA before amplification.

Question 19: A faint band below 100 bp appears in every lane, including the NTC. What is it most likely?

Degraded genomic DNA
Primer dimer (Correct answer)
Plasmid contamination
The specific target amplicon

Correct answer: Primer dimer

Primer dimers are short artifacts that form even without template and run below about 100 bp.

Question 20: Why is Taq polymerase preferred in PCR?

It binds RNA.
It denatures DNA.
It is heat-stable and synthesizes DNA (Correct answer)
It functions at low pH.

Correct answer: It is heat-stable and synthesizes DNA

Taq polymerase is preferred in PCR because of its exceptional heat-stability. Unlike most enzymes, it can withstand the high temperatures (94-95°C) required to denature DNA in each PCR cycle without degrading. This allows the enzyme to remain active throughout multiple cycles, efficiently synthesizing new DNA strands and making the PCR process automated and highly effective.

Question 21: Which statement about a data availability statement is correct?

It tells readers where and how the underlying data can be accessed, such as repository accession numbers (Correct answer)
It is needed only for clinical trials
It is the same as the conflict-of-interest statement
It lists the funding agencies

Correct answer: It tells readers where and how the underlying data can be accessed, such as repository accession numbers

A data availability statement points readers to the data behind the findings, often through repository accession numbers.

Question 22: A strong band under 100 bp appears in both samples and the no-template control. Which change best reduces it?

Increase primer concentration
Lower the annealing temperature
Use hot-start polymerase and raise the annealing temperature (Correct answer)
Lengthen the extension step

Correct answer: Use hot-start polymerase and raise the annealing temperature

Primer-dimers form at low temperatures before or during cycling, and hot-start enzymes plus higher stringency reduce them.

Question 23: Which anticoagulant is generally preferred for blood samples intended for PCR testing?

Sodium fluoride
EDTA (Correct answer)
Heparin
Sodium citrate with heparin

Correct answer: EDTA

EDTA is preferred because heparin strongly inhibits PCR and is difficult to remove during extraction.

Question 24: Which PCR-based diagnostic test is used in US clinical labs to differentiate influenza A, influenza B, and RSV in respiratory specimens from a single sample?

Multiplex real-time RT-PCR panel (Correct answer)
Pyrosequencing
Southern blot hybridization
Single-plex endpoint PCR

Correct answer: Multiplex real-time RT-PCR panel

Multiplex real-time RT-PCR panels allow simultaneous detection and differentiation of multiple respiratory viruses from one specimen, improving turnaround time and resource efficiency.

Question 25: A trend chart shows NTC Ct values moving from undetected to Ct 36, then Ct 33 over several weeks. This pattern suggests:

Instrument calibration drift only
Improved assay sensitivity
Contamination building up that needs investigation before it affects results (Correct answer)
Normal run-to-run variation

Correct answer: Contamination building up that needs investigation before it affects results

Earlier and earlier NTC Ct values mean a growing contaminant load in the lab or reagents.

Question 26: A standard curve has a slope of -3.32. What amplification efficiency does this correspond to?

About 100% (Correct answer)
About 90%
About 110%
About 80%

Correct answer: About 100%

Efficiency = 10^(-1/slope) - 1, and a slope of -3.32 gives about 100% (perfect doubling each cycle).

Question 27: Which step in PCR involves the separation of DNA strands?

Denaturation (Correct answer)
Transcription
Elongation
Annealing

Correct answer: Denaturation

The denaturation step in PCR involves the separation of the double-stranded DNA template into two single strands. This occurs at a high temperature, typically 94–95°C, which breaks the hydrogen bonds between complementary base pairs. Separating the strands makes the DNA accessible for the primers to bind in the subsequent annealing step, initiating the amplification process.

Question 28: What is the effect of excessive Mg2+ concentration in a PCR reaction?

Lower fidelity and more nonspecific amplification (Correct answer)
Complete loss of polymerase activity
Faster primer degradation
Lower template melting temperature

Correct answer: Lower fidelity and more nonspecific amplification

High Mg2+ stabilizes mismatched primer binding and lowers fidelity, producing extra bands.

Question 29: In environmental DNA (eDNA) surveys, a field blank (filtered sterile water carried to the site) is used to detect:

Degradation of target DNA during transport
Inhibition in the extraction kit
Contamination introduced during field sampling and handling (Correct answer)
Low filter pore efficiency

Correct answer: Contamination introduced during field sampling and handling

Field blanks go through the same handling as real samples to show contamination added in the field.

Question 30: In oncology diagnostics, which PCR-based method is used to detect minimal residual disease (MRD) in leukemia patients?

Nested PCR
Quantitative real-time PCR (qPCR) (Correct answer)
Asymmetric PCR
Colony PCR

Correct answer: Quantitative real-time PCR (qPCR)

qPCR is used for MRD detection because it can quantify extremely low levels of residual leukemic cells with high sensitivity.

Question 31: Which PCR technique is used to identify single nucleotide polymorphisms (SNPs) associated with drug metabolism in pharmacogenomics?

Long-range PCR
Ligation-mediated PCR
Allele-specific PCR (Correct answer)
Inverse PCR

Correct answer: Allele-specific PCR

Allele-specific PCR uses primers designed to amplify only one allele, making it ideal for distinguishing SNP variants relevant to pharmacogenomics.

Question 32: What is the main purpose of hot-start PCR?

To speed up the denaturation step
To remove RNA contamination from the sample
To prevent polymerase activity at low temperatures that causes mispriming and primer-dimers (Correct answer)
To increase the processivity of the enzyme

Correct answer: To prevent polymerase activity at low temperatures that causes mispriming and primer-dimers

Hot-start methods block polymerase activity until the first high-temperature step, reducing nonspecific products formed during setup.

Question 33: What is the primary instrumental advantage of a gradient thermal cycler?

It provides faster ramp rates than standard cyclers
It tests several annealing temperatures across the block in a single run (Correct answer)
It measures fluorescence in real time
It eliminates the need for a heated lid

Correct answer: It tests several annealing temperatures across the block in a single run

A gradient block holds different columns at different temperatures, so annealing conditions can be optimized in one run.

Question 34: Where should the fluorescence threshold be set for reliable Ct determination?

Below the baseline
At the plateau phase
At the very first cycle
Within the exponential phase, above baseline noise (Correct answer)

Correct answer: Within the exponential phase, above baseline noise

Setting the threshold in the exponential phase, where amplification is most consistent, gives reproducible Ct values.

Question 35: In agricultural diagnostics, which PCR application is used by US regulatory agencies to verify the presence of approved genetically modified (GMO) crops?

Random amplified polymorphic DNA (RAPD) PCR
Event-specific PCR targeting transgene insertion sites (Correct answer)
Inverse PCR
In situ PCR

Correct answer: Event-specific PCR targeting transgene insertion sites

Event-specific PCR amplifies the unique genomic junction between the inserted transgene and host plant DNA, providing definitive identification of a specific approved GMO event.

Question 36: Which characteristic BEST describes a successful quality assurance & control culture in Polymerase Chain Reaction?

Top-down directives without employee input
Periodic campaigns without sustained effort
Continuous learning where all team members actively seek improvement (Correct answer)
Focus on compliance over genuine improvement

Correct answer: Continuous learning where all team members actively seek improvement

A culture where all team members actively seek improvement opportunities creates sustainable quality enhancement across the organization.

Question 37: Which emerging PCR-based technology uses CRISPR-Cas systems coupled with PCR amplification to provide highly specific visual detection results for point-of-care infectious disease testing?

Hot-start PCR with melt curve analysis
Conventional multiplex PCR
Digital droplet PCR
SHERLOCK (Specific High-sensitivity Enzymatic Reporter unLOCKing) (Correct answer)

Correct answer: SHERLOCK (Specific High-sensitivity Enzymatic Reporter unLOCKing)

SHERLOCK combines isothermal amplification with CRISPR-Cas13 cleavage of a reporter molecule, generating a visible or fluorescent signal specific to the target nucleic acid.

Question 38: In Polymerase Chain Reaction, how should environmental monitoring & assessment results be communicated to stakeholders?

Through clear, structured reports with actionable recommendations (Correct answer)
Using technical jargon without explanation
Only when specifically requested
Verbally without written documentation

Correct answer: Through clear, structured reports with actionable recommendations

Clear, structured reports with actionable recommendations ensure stakeholders understand findings and can take appropriate action.

Question 39: Which error statistic should a figure legend use to show how much individual biological replicates vary?

Standard error of the mean (SEM)
95% confidence interval of the mean
Coefficient of determination (R²)
Standard deviation (SD) (Correct answer)

Correct answer: Standard deviation (SD)

SD describes the spread of individual data points, while SEM describes how precisely the mean is estimated.

Question 40: When a researcher observes multiple non-specific bands on an agarose gel after PCR, which primer design issue is the most likely cause?

Primers that are too long (> 30 nt)
Primers with a Tm that is too high relative to the annealing temperature used
Primers stored at -20°C before use
Primers with low specificity due to sequences complementary to multiple genomic loci (Correct answer)

Correct answer: Primers with low specificity due to sequences complementary to multiple genomic loci

Non-specific banding occurs when primers share homology with off-target genomic sites, causing amplification of unintended products alongside the target.

Question 41: A background calibration on a qPCR instrument is performed using:

A serial dilution of a known template
An empty instrument with no plate loaded
A plate containing buffer or water without fluorescent dyes (Correct answer)
A plate containing each pure dye

Correct answer: A plate containing buffer or water without fluorescent dyes

Background calibration measures fluorescence from the plate, buffer, and optics so it can be subtracted from experimental data.

Question 42: Which PCR application is used to diagnose genetic disorders prenatally by analyzing cell-free fetal DNA in maternal blood?

Reverse complement PCR
Hot-start PCR
Non-invasive prenatal testing (NIPT) using qPCR (Correct answer)
In situ PCR

Correct answer: Non-invasive prenatal testing (NIPT) using qPCR

NIPT uses qPCR or next-generation sequencing on cell-free fetal DNA circulating in maternal plasma to detect chromosomal abnormalities.

Question 43: What is the main purpose of gradient PCR?

To test a range of annealing temperatures in one run to find the optimum (Correct answer)
To convert RNA into cDNA
To quantify product in real time
To amplify several targets at once

Correct answer: To test a range of annealing temperatures in one run to find the optimum

A gradient thermal block runs different annealing temperatures across columns at the same time.

Question 44: What is the PRIMARY benefit of documenting research methodology & design in Polymerase Chain Reaction?

Creating a reference for quality assurance, training, and continuous improvement (Correct answer)
Reducing the workload for future practitioners
Protecting against client complaints only
Meeting minimum paperwork requirements

Correct answer: Creating a reference for quality assurance, training, and continuous improvement

Documentation serves multiple purposes including quality assurance, training resources, and a foundation for continuous improvement.

Question 45: In veterinary diagnostics, which PCR application is used by USDA-approved laboratories to detect foot-and-mouth disease virus (FMDV) in suspect animal specimens?

Standard endpoint RT-PCR only
Isothermal PCR at 37°C
LAMP without real-time detection
Real-time RT-PCR for rapid confirmatory diagnosis (Correct answer)

Correct answer: Real-time RT-PCR for rapid confirmatory diagnosis

Real-time RT-PCR is the USDA-approved gold standard for rapid FMDV detection due to its high sensitivity, specificity, and ability to provide results within hours.

Question 46: What is the typical temperature for the denaturation step in PCR?

94–95°C (Correct answer)
70–72°C
20–25°C
40–50°C

Correct answer: 94–95°C

The denaturation step in PCR requires a high temperature to separate the double-stranded DNA template into single strands. A typical temperature for this step is 94–95°C. This heat is sufficient to break the hydrogen bonds between complementary base pairs, making the DNA accessible for primer binding in the subsequent annealing step.

Question 47: Why should lab coats used in the post-PCR area never be worn into the pre-PCR area?

Pre-PCR rooms require sterile gowns only
Coats interfere with laminar airflow
They can carry amplicons that contaminate clean reagents and setups (Correct answer)
Post-PCR coats are not flame resistant

Correct answer: They can carry amplicons that contaminate clean reagents and setups

PPE worn in amplification areas collects amplified DNA and moves it into clean zones.

Question 48: The limit of detection (LOD) for a clinical PCR assay is commonly defined as the lowest concentration that is:

Quantified with less than 5% CV
Below the NTC Ct value
Detected in at least 95% of replicates (Correct answer)
Detected in at least 50% of replicates

Correct answer: Detected in at least 95% of replicates

LOD is usually the lowest concentration detected in at least 95% of replicate tests.

Question 49: Which practice is the main regulatory and accreditation expectation for preventing amplicon carryover contamination in a clinical PCR lab?

Opening amplified tubes in the reagent prep room
Running all steps on one bench to save time
Sharing pipettes between all areas
Physically separated pre- and post-amplification areas with unidirectional workflow (Correct answer)

Correct answer: Physically separated pre- and post-amplification areas with unidirectional workflow

Accreditation checklists expect separate pre- and post-PCR areas and a one-way workflow to prevent amplicon contamination.

Question 50: A qPCR standard curve has a slope of -3.32. What amplification efficiency does this indicate?

About 50%
About 150%
About 100% (Correct answer)
About 75%

Correct answer: About 100%

Efficiency = 10^(-1/slope) - 1, and a slope of -3.32 gives about 100%.

Question 51: In the ΔΔCt method, a target gene shows a ΔΔCt of -2. What is its fold change relative to the calibrator, assuming 100% efficiency?

-2-fold
2-fold
0.25-fold
4-fold increase (Correct answer)

Correct answer: 4-fold increase

Fold change = 2^-ΔΔCt = 2^2 = 4.

Question 52: Which specification should be verified on a Certificate of Analysis (CoA) when receiving a new lot of dNTPs for PCR to ensure reagent quality?

Color of the solution
Osmolality of the solution
Viscosity measurements
Purity (≥99%) and absence of nuclease contamination (Correct answer)

Correct answer: Purity (≥99%) and absence of nuclease contamination

High purity dNTPs (≥99% by HPLC) and confirmed absence of DNase/RNase are critical quality parameters on a CoA that directly affect PCR performance and reliability.

Question 53: When facing an unfamiliar challenge in specimen collection & handling within Polymerase Chain Reaction, what is the BEST approach?

Avoid the challenge if possible
Apply the most familiar technique regardless of suitability
Attempt to resolve it independently without consultation
Research established best practices, consult colleagues, and document the approach (Correct answer)

Correct answer: Research established best practices, consult colleagues, and document the approach

Researching best practices and consulting colleagues combines established knowledge with practical experience, while documentation supports future reference.

Question 54: What is the primary purpose of PCR in molecular biology?

To analyze protein structure.
To amplify DNA segments. (Correct answer)
To sequence RNA.
To cut DNA into fragments.

Correct answer: To amplify DNA segments.

The primary purpose of Polymerase Chain Reaction (PCR) in molecular biology is to amplify specific segments of DNA. This technique allows scientists to make millions of copies from even a tiny amount of DNA, enabling detailed study and analysis. PCR is invaluable for various applications, including genetic testing, forensic analysis, and disease diagnosis, by providing sufficient material for further research.

Question 55: Why do Taq-generated PCR products suit TA cloning?

Taq adds a single non-templated 3' adenine overhang (Correct answer)
They have blunt ends
They carry 5' phosphate overhangs
They contain built-in restriction sites

Correct answer: Taq adds a single non-templated 3' adenine overhang

Taq's terminal transferase activity leaves a 3' A that pairs with the 3' T overhang of TA vectors.

Question 56: In infectious disease surveillance, which PCR approach enables point-of-care testing by completing amplification in under 30 minutes without a thermocycler?

Conventional PCR
Nested PCR
Touchdown PCR
Loop-mediated isothermal amplification (LAMP) (Correct answer)

Correct answer: Loop-mediated isothermal amplification (LAMP)

LAMP uses a strand-displacing polymerase at a constant temperature, eliminating the need for a thermocycler and enabling rapid point-of-care diagnostic use.

Question 57: Which adjustment to a gel image is generally acceptable for publication?

Increasing contrast only in the lane of interest
Cloning background over a smear
Brightness/contrast applied evenly across the whole image (Correct answer)
Erasing a faint nonspecific band

Correct answer: Brightness/contrast applied evenly across the whole image

Linear adjustments applied to the whole image are acceptable; local edits that remove or enhance features are not.

Question 58: Why should lab coats be dedicated to specific areas (pre-PCR vs. post-PCR)?

Because post-PCR coats must be flame-resistant
To prevent amplicons on clothing from being carried into clean areas (Correct answer)
To meet color-coding rules for visitors only
Because pre-PCR areas require sterile surgical gowns

Correct answer: To prevent amplicons on clothing from being carried into clean areas

Area-specific coats prevent transfer of amplified DNA on clothing into reagent and sample preparation spaces.

Question 59: Which federal agency administers the CLIA program, including certification and laboratory inspections?

Centers for Medicare & Medicaid Services (CMS) (Correct answer)
Food and Drug Administration (FDA)
Centers for Disease Control and Prevention (CDC)
Occupational Safety and Health Administration (OSHA)

Correct answer: Centers for Medicare & Medicaid Services (CMS)

CMS administers CLIA certification, fees, and surveys, while FDA categorizes test complexity and CDC provides technical support.

Question 60: Which PCR technique is used in newborn screening programs in the US to detect mutations causing conditions like spinal muscular atrophy (SMA)?

Rolling circle amplification
Multiplex ligation-dependent probe amplification (MLPA) (Correct answer)
Inverse PCR
Asymmetric PCR

Correct answer: Multiplex ligation-dependent probe amplification (MLPA)

MLPA uses PCR amplification of ligation products to detect copy number variations and point mutations, making it suitable for newborn screening panels.

Question 61: What temperature range is used for primer annealing?

30°C
75°C
50–65°C (Correct answer)
90°C

Correct answer: 50–65°C

The primer annealing step in PCR occurs at a specific temperature range, typically 50–65°C. This temperature is crucial because it allows the short DNA primers to bind specifically to their complementary sequences on the single-stranded DNA template. The optimal annealing temperature is determined by the melting temperature of the primers and ensures specific amplification while minimizing non-specific binding.

Question 62: How does digital PCR (dPCR) quantify nucleic acids without a standard curve?

By measuring Ct values against a reference gene
By measuring band intensity on a gel
By melt curve analysis
By partitioning the sample into many reactions and counting positive partitions with Poisson statistics (Correct answer)

Correct answer: By partitioning the sample into many reactions and counting positive partitions with Poisson statistics

The fraction of positive partitions, corrected with Poisson statistics, gives absolute copy number.

Question 63: A paper uses the abbreviation 'NTC' throughout. What is the correct practice?

Define it only in a glossary at the end
Spell it out at first use in the text, followed by the abbreviation in parentheses (Correct answer)
Define it only in the figure legends
Never define it because it is common

Correct answer: Spell it out at first use in the text, followed by the abbreviation in parentheses

Abbreviations should be defined at first mention, for example 'no-template control (NTC)'.

Question 64: A VTM tube arrives with the specimen leaked into the transport bag. What is the appropriate action?

Test the remaining liquid as usual
Add fresh VTM and proceed
Reject the specimen and request recollection (Correct answer)
Wipe the tube and report normally

Correct answer: Reject the specimen and request recollection

Leaked specimens pose contamination and safety risks and may have compromised volume or integrity.

Question 65: A researcher changes a value in a paper lab notebook. Which correction method preserves data integrity?

Cover it with correction fluid and initial it
Tear out the page and rewrite it
Erase the value and write the new one
Draw a single line through it, write the correction, then initial and date it (Correct answer)

Correct answer: Draw a single line through it, write the correction, then initial and date it

A single strikethrough keeps the original entry readable and creates a traceable audit trail.

Question 66: Which quality assurance & control tool is MOST valuable for identifying root causes in Polymerase Chain Reaction?

Blame assignment without investigation
Quick fixes based on symptoms
Historical trend analysis alone
Root cause analysis with systematic investigation methods (Correct answer)

Correct answer: Root cause analysis with systematic investigation methods

Root cause analysis with systematic methods identifies underlying causes rather than symptoms, leading to lasting solutions.

Question 67: What is the main drawback of SYBR Green chemistry compared with probe-based qPCR?

It cannot be used with DNA templates
It needs a reverse transcriptase
It only works with multiplex reactions
It binds any double-stranded DNA, including primer-dimers and nonspecific products (Correct answer)

Correct answer: It binds any double-stranded DNA, including primer-dimers and nonspecific products

SYBR Green is not sequence-specific, so any dsDNA adds to the signal.

Question 68: What enzyme is required in the first step of RT-PCR?

DNA ligase
Reverse transcriptase (Correct answer)
RNase H only
Restriction endonuclease

Correct answer: Reverse transcriptase

Reverse transcriptase synthesizes cDNA from an RNA template, which is then amplified by PCR.

Question 69: How often should quality assurance & control metrics be reviewed in Polymerase Chain Reaction?

Regularly at defined intervals with additional reviews triggered by significant events (Correct answer)
When external audits are scheduled
Only during annual performance reviews
When problems are reported

Correct answer: Regularly at defined intervals with additional reviews triggered by significant events

Regular scheduled reviews ensure ongoing monitoring while event-triggered reviews capture the impact of significant changes.

Question 70: Why are PCR master mixes typically prepared with roughly 10% excess volume?

To increase the final primer concentration
To allow the mix to evaporate during cycling
To dilute PCR inhibitors in the samples
To compensate for pipetting losses so every reaction receives a full volume (Correct answer)

Correct answer: To compensate for pipetting losses so every reaction receives a full volume

Extra volume covers dead volume and pipetting losses so the last reaction is not short.

Question 71: After a SYBR Green qPCR run, a melt curve shows two distinct peaks. What does this most likely indicate?

The reference dye failed
The template was degraded RNA
Perfect single-product amplification
More than one product, such as a primer-dimer alongside the target (Correct answer)

Correct answer: More than one product, such as a primer-dimer alongside the target

Each distinct melting peak reflects a dsDNA species with a different Tm.

Question 72: What is the typical denaturation temperature range in standard PCR?

50-65°C
37-42°C
94-98°C (Correct answer)
68-72°C

Correct answer: 94-98°C

Temperatures of 94-98°C separate dsDNA strands without destroying a thermostable polymerase over normal cycling.

Question 73: Why is the plateau phase not used for quantification in real-time PCR?

The polymerase is inactive during the plateau
Fluorescence cannot be detected in the plateau
Reagents become limiting, so the final yield no longer reflects the starting quantity (Correct answer)
The plateau happens before the baseline

Correct answer: Reagents become limiting, so the final yield no longer reflects the starting quantity

In the plateau, depleted reagents and product reannealing break the link between yield and starting template.

Question 74: In tissue typing for organ transplantation, which PCR-based approach is used to determine HLA compatibility between donor and recipient?

Inverse PCR
Overlap extension PCR
Emulsion PCR
Sequence-specific primer PCR (PCR-SSP) (Correct answer)

Correct answer: Sequence-specific primer PCR (PCR-SSP)

PCR-SSP uses primer pairs designed to amplify only specific HLA alleles, enabling rapid and accurate HLA typing for transplant matching.

Question 75: Using a standard Taq polymerase, approximately what extension time is recommended for a 3 kb amplicon?

About 30 seconds
About 15 minutes
About 10 seconds
About 3 minutes (Correct answer)

Correct answer: About 3 minutes

Taq extends at roughly 1 kb per minute, so a 3 kb product needs about 3 minutes.

Question 76: What is the role of primers in PCR?

Start DNA synthesis at specific sites (Correct answer)
Break DNA strands
Bind to proteins
Act as enzymes

Correct answer: Start DNA synthesis at specific sites

Primers are short, synthetic DNA sequences that are crucial for initiating DNA synthesis in PCR. They bind to specific, complementary regions at the ends of the target DNA segment during the annealing step. This binding provides a starting point for the Taq polymerase enzyme to begin synthesizing new DNA strands, ensuring that only the desired region of the DNA is amplified.

Question 77: Which section of the Federal Food, Drug, and Cosmetic Act lets the FDA authorize unapproved diagnostic tests during a declared emergency?

Section 201(h)
Section 505(b)(2)
Section 510(k)
Section 564 Emergency Use Authorization (Correct answer)

Correct answer: Section 564 Emergency Use Authorization

Section 564 lets FDA issue EUAs, as it did widely for SARS-CoV-2 PCR tests.

Question 78: What is the PRIMARY objective of regulatory standards & compliance in the Polymerase Chain Reaction field?

To limit the scope of professional practice
To increase operational costs for organizations
To ensure adherence to established standards and protect stakeholders (Correct answer)
To create additional paperwork for professionals

Correct answer: To ensure adherence to established standards and protect stakeholders

The primary objective of compliance and regulatory frameworks is to ensure adherence to standards that protect stakeholders.

Question 79: Which clinical PCR application is FDA-cleared and used to rapidly identify antimicrobial resistance genes (e.g., mecA for MRSA) directly from positive blood cultures?

Endpoint PCR with gel electrophoresis
Microarray-based hybridization only
Conventional culture and sensitivity testing
Multiplex real-time PCR panels for bloodstream infection (Correct answer)

Correct answer: Multiplex real-time PCR panels for bloodstream infection

FDA-cleared multiplex real-time PCR panels such as the FilmArray BCID can identify pathogens and resistance genes directly from blood culture bottles within one hour.

Question 80: How should a clinical PCR report express a qualitative result for a pathogen target that was not amplified?

"Not detected" (Correct answer)
"Inconclusive"
"Negative — pathogen absent"
"Cq = 0"

Correct answer: "Not detected"

"Not detected" reflects the assay's detection limit without claiming the pathogen is truly absent.

Question 81: For detection of tick-borne diseases such as Lyme disease in the US, which PCR specimen type is most clinically useful for direct pathogen detection?

Skin biopsy from the erythema migrans lesion (Correct answer)
Whole blood collected during antibiotic therapy
Cerebrospinal fluid in all cases
Serum collected 4 weeks after symptom onset

Correct answer: Skin biopsy from the erythema migrans lesion

Skin biopsy from the erythema migrans rash has the highest PCR sensitivity for Borrelia burgdorferi detection during early Lyme disease.

Question 82: Identical reactions in edge wells of a 96-well block keep giving lower yields than center wells. What is the most likely cause?

Primer degradation
Contamination in the master mix
Wrong primer sequences
Uneven temperature across the thermal block (Correct answer)

Correct answer: Uneven temperature across the thermal block

Poor block uniformity, often at the edges, means some wells don't reach the right temperatures, so the instrument should be checked with a temperature verification kit.

Question 83: For food safety testing in the US, which PCR method allows detection of multiple pathogens such as Salmonella and E. coli simultaneously in a single reaction?

Booster PCR
Multiplex PCR (Correct answer)
Isothermal PCR
Touch-down PCR

Correct answer: Multiplex PCR

Multiplex PCR uses multiple primer pairs in one reaction tube to detect several pathogens simultaneously, making food safety screening faster and more cost-effective.

Question 84: Why does PCR eventually reach a plateau phase?

Reagents run out, the polymerase loses activity, and products reanneal to each other (Correct answer)
The primers become longer each cycle
The template becomes single-stranded permanently
Fluorescence detection saturates the instrument only

Correct answer: Reagents run out, the polymerase loses activity, and products reanneal to each other

Late cycles slow down as dNTPs and primers deplete, enzyme activity drops, and product strands compete with primers.

Question 85: Two consecutive control results both exceed +2 SD on the same side of the mean. This pattern most likely reflects:

Random pipetting error
Normal expected variation
Systematic error such as a reagent or calibration shift (Correct answer)
Sample mix-up

Correct answer: Systematic error such as a reagent or calibration shift

Violating the 2-2s rule points to systematic error, such as a reagent lot or calibration shift.

Question 86: A patient sample shows a delayed internal control Ct (8 cycles later than expected) and no target amplification. What is the best next step?

Report as positive
Report as negative
Suspect inhibition; dilute or re-extract the sample and retest (Correct answer)
Replace the thermal cycler

Correct answer: Suspect inhibition; dilute or re-extract the sample and retest

A strongly delayed IAC signals inhibition, so the negative result is unreliable and dilution or re-extraction is needed.

Question 87: Which polymerase property allows Pfu polymerase to have higher fidelity than Taq polymerase?

Terminal transferase activity
3'→5' exonuclease (proofreading) activity (Correct answer)
Reverse transcriptase activity
5'→3' exonuclease activity

Correct answer: 3'→5' exonuclease (proofreading) activity

The 3'→5' exonuclease removes misincorporated nucleotides, lowering the error rate.

Question 88: What is the primary purpose of performing a gradient PCR when optimizing primer annealing?

To determine the optimal extension time for the product
To test the stability of the DNA template
To measure primer concentration effects on amplification
To identify the annealing temperature that yields the highest specificity and yield (Correct answer)

Correct answer: To identify the annealing temperature that yields the highest specificity and yield

Gradient PCR tests multiple annealing temperatures simultaneously, allowing selection of the optimal Ta that maximizes product specificity and yield.

Question 89: What is the purpose of a passive reference dye such as ROX in qPCR?

To serve as the reverse transcription primer
To quench the reporter dye
To normalize for well-to-well differences in fluorescence unrelated to amplification (Correct answer)
To measure the product's melting temperature

Correct answer: To normalize for well-to-well differences in fluorescence unrelated to amplification

ROX corrects for pipetting volume differences and optical variation across wells.

Question 90: What is the function of the heated lid on a thermal cycler?

It speeds up the denaturation step
It sterilizes the outside of the tubes
It provides the annealing temperature
It prevents condensation and evaporation of the reaction onto the tube cap (Correct answer)

Correct answer: It prevents condensation and evaporation of the reaction onto the tube cap

Heating the lid above the block temperature keeps vapor from condensing on caps, maintaining reaction volume.

Question 91: Where should raw high-throughput sequencing reads from an amplicon study usually be deposited before publication?

A personal cloud folder linked in the acknowledgments
The supplementary PDF of the paper
The NCBI Sequence Read Archive (SRA) (Correct answer)
The lab's internal shared drive only

Correct answer: The NCBI Sequence Read Archive (SRA)

Raw sequencing reads belong in a public repository like SRA, with accession numbers cited in the data availability statement.

Question 92: Which sampling approach is best for recovering DNA contamination from a pipette barrel surface?

Dry cotton swab rubbed briefly
Adhesive tape lift followed by autoclaving
Air settle plate placed beside the pipette
Swab moistened with sterile, nuclease-free water or buffer (Correct answer)

Correct answer: Swab moistened with sterile, nuclease-free water or buffer

A moistened swab picks up dried nucleic acid from surfaces much better than a dry swab.

Question 93: Diluting a sample 1:10 causes it to amplify earlier (lower Ct) than the undiluted sample. What does this suggest?

The undiluted sample contains PCR inhibitors (Correct answer)
The assay efficiency is above 100% because of the probe
The threshold was set too low
The diluted sample was contaminated with genomic DNA

Correct answer: The undiluted sample contains PCR inhibitors

Dilution lowers inhibitor concentration, so amplification improves even though there is less template.

Question 94: A low A260/A230 ratio (e.g., 0.9) in a nucleic acid extract most often indicates carryover of:

Genomic DNA
Guanidine salts, carbohydrates, or phenol (Correct answer)
Intact RNA
EDTA-free buffer

Correct answer: Guanidine salts, carbohydrates, or phenol

Chaotropic salts such as guanidine and other organic contaminants absorb strongly at 230 nm, which lowers the ratio below the ideal ~2.0-2.2.

Question 95: In a unidirectional PCR workflow, where should incoming patient specimens be opened and processed?

In the pre-amplification specimen processing area (Correct answer)
At the thermal cycler bench
In the post-amplification area
In the gel electrophoresis room

Correct answer: In the pre-amplification specimen processing area

Specimens must stay in pre-amplification areas to avoid exposure to amplified products.

Question 96: Why should sample processing order be randomized across treatment groups?

To reduce reagent costs
To prevent time-dependent drift from being confounded with treatment (Correct answer)
To increase amplification efficiency
To eliminate the need for controls

Correct answer: To prevent time-dependent drift from being confounded with treatment

Randomization distributes unknown systematic effects evenly across groups.

Question 97: For RT-PCR, which practice best protects RNA samples from degradation during handling?

Storing RNA at 4 °C for several months
Using RNase-free reagents and plasticware, changing gloves often, and treating surfaces with an RNase decontaminant (Correct answer)
Working without gloves to improve dexterity
Using tap water to dilute RNA

Correct answer: Using RNase-free reagents and plasticware, changing gloves often, and treating surfaces with an RNase decontaminant

RNases are ubiquitous and stable, so RNase-free materials and surface decontamination are essential.

Question 98: Degenerate primers are most useful when:

Amplifying from plasmid controls
Only the protein sequence or related gene sequences are known (Correct answer)
The target sequence is known exactly
Performing digital PCR

Correct answer: Only the protein sequence or related gene sequences are known

Degenerate primers are mixtures covering possible codon variants, so they can amplify related or partly unknown sequences.

Question 99: On camera-based qPCR instruments, a Region of Interest (ROI) calibration is used to:

Determine amplification efficiency
Verify heated lid temperature
Set the cycle threshold automatically
Map the location of each well on the detector (Correct answer)

Correct answer: Map the location of each well on the detector

ROI calibration tells the instrument which detector pixels correspond to each well.

Question 100: How can optimization improve PCR efficiency?

Shortens primers
Reduces denaturation
Enhances product quality and consistency (Correct answer)
Lowers enzyme use

Correct answer: Enhances product quality and consistency

PCR optimization involves fine-tuning various reaction parameters such as primer concentration, MgCl₂ concentration, annealing temperature, and enzyme amount. By systematically adjusting these conditions, researchers can significantly improve the specificity, sensitivity, and yield of the PCR. This leads to higher quality, more consistent, and reliable results, making the assay more efficient and robust.

ASCP Technologist in Molecular Biology (MB) Certification Exam

The MB(ASCP) certification exam evaluates competency in molecular biology laboratory science, including nucleic acid chemistry, PCR amplification techniques, laboratory operations, and clinical applications of molecular diagnostics.

100

Questions

150 min

Time Limit

70%

To Pass

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