Quality Assurance in DNA Testing — MCQs

10 questions

For DNA test, liquid blood is preserved in:

Arrange the following in sequential order with regards to the steps of collection of samples for pap smear testing: Use posterior vaginal wall retractor Take the sample Make smear on a slide Fix the smear

In vitro DNA amplification is done by

Which test is used for detecting gunshot residue?

Which of the following statements accurately describes the relationship between quality assurance (QA), quality control (QC), internal quality assurance (IQA), and external quality assurance (EQA)?

What is the technique for accurate quantification of gene expression?

Which of the following statements about nucleic acid amplification tests (NAATs) for STIs is FALSE?

DNA fingerprinting is used for paternity testing and forensic identification of suspects. Which of the following is the most accurate description of DNA fingerprinting?

DNA fingerprinting can be done with all, except:

Q10

Disputed maternity can be solved by using the following tests, EXCEPT:

Quality Assurance in DNA Testing Indian Medical PG Practice Questions and MCQs

Question 1: For DNA test, liquid blood is preserved in:

A. Sodium fluoride
B. Potassium oxalate
C. Sodium citrate
D. EDTA (Correct Answer)

Explanation: ***EDTA*** - Ethylenediaminetetraacetic acid (EDTA) is the preferred anticoagulant for DNA extraction because it **chelates metal ions** (like magnesium), which are cofactors for **DNases** (enzymes that degrade DNA). - By inhibiting DNases, EDTA effectively **preserves DNA integrity** in blood samples for genetic testing. *Sodium fluoride* - **Sodium fluoride** is primarily used as an antiglycolytic agent to preserve glucose in blood samples. - It does not specifically function to preserve DNA or inhibit DNA degradation significantly. *Potassium oxalate* - **Potassium oxalate** acts as an anticoagulant by precipitating calcium, but it is not optimal for long-term DNA preservation. - Its anticoagulant properties are less suitable for molecular testing compared to EDTA, and it doesn't protect DNA as effectively. *Sodium citrate* - **Sodium citrate** is an anticoagulant primarily used for coagulation studies (e.g., PT, PTT) by chelating calcium. - While it prevents clotting, it is **less effective than EDTA** in protecting DNA from degradation by DNases, making it a poorer choice for DNA banking.

Question 2: Arrange the following in sequential order with regards to the steps of collection of samples for pap smear testing: Use posterior vaginal wall retractor Take the sample Make smear on a slide Fix the smear

A. 1,2,4,3
B. 3,1,2,4
C. 1,2,3,4 (Correct Answer)
D. 2,1,3,4

Explanation: ***1,2,3,4*** - The correct sequence for collecting a Pap smear involves first **visualizing the cervix** using a posterior vaginal wall retractor, then **taking the sample** (e.g., using a broom or spatula and brush), followed by **making a smear on a slide** and finally **fixing the smear** to preserve the cells. - This sequential order ensures proper cell collection and preservation for accurate cytological examination. *1,2,4,3* - This option incorrectly places **fixing the smear** before **making the smear on the slide**. Cells must first be spread onto the slide before they can be fixed. - Fixing an un-smeared sample or attempting to smear after fixing would lead to an inadequate or damaged specimen. *3,1,2,4* - This sequence incorrectly starts with **making a smear on a slide** before any sample has been collected or the cervix visualized. - One cannot make a smear without first taking a sample and accessing the cervix via a retractor. *2,1,3,4* - This option incorrectly states that **taking the sample** occurs before **using a posterior vaginal wall retractor**. The retractor is essential for proper visualization and access to the cervix to obtain a quality sample. - Attempting to take a sample without proper visualization would lead to an inadequate or incorrect specimen collection.

Question 3: In vitro DNA amplification is done by

A. Recombinant technique
B. Polymerase chain reaction (Correct Answer)
C. Electrophoresis
D. Blotting technique

Explanation: ***Polymerase chain reaction*** - **Polymerase chain reaction (PCR)** is an in vitro technique used to amplify specific DNA sequences, creating millions of copies from a small initial sample. - It involves cycles of **denaturation** (94-96°C), **annealing** (50-65°C), and **extension** (72°C) using a heat-stable DNA polymerase like **Taq polymerase**. - PCR is the gold standard for in vitro DNA amplification, requiring only a **thermocycler**, primers, dNTPs, and DNA polymerase. *Recombinant technique* - **Recombinant DNA technology** involves combining DNA from different sources to create new genetic material for gene expression or cloning. - It utilizes **restriction enzymes** and **ligases** to insert DNA into vectors, which are then replicated within **host organisms** (bacteria, yeast) - this is primarily an **in vivo** process, not in vitro amplification. *Electrophoresis* - **Electrophoresis** is a separation technique used to resolve DNA fragments, RNA, or proteins based on size and charge through a gel matrix. - It does not amplify DNA; it's used for **analysis** and **visualization** of DNA samples after amplification or other manipulations. *Blotting technique* - **Blotting techniques** (Southern blot for DNA, Northern blot for RNA, Western blot for proteins) detect specific macromolecules after gel electrophoresis. - These methods transfer molecules to membranes and use labeled probes for **identification and detection**, not amplification.

Question 4: Which test is used for detecting gunshot residue?

A. Lie test for Firearm injury
B. Neutron activation analysis for firearm use (Correct Answer)
C. Toluidine blue test
D. Benzidine test for blood stain

Explanation: ***Neutron activation analysis for firearm use*** - **Neutron activation analysis (NAA)** is a highly sensitive and reliable method for detecting specific elements characteristic of **gunshot residue (GSR)**, such as **barium**, **antimony**, and **lead**. - This technique works by irradiating samples with neutrons, causing them to emit gamma rays that are unique to each element, allowing for precise identification and quantification of GSR particles. *Lie test for Firearm injury* - A "lie test" typically refers to a **polygraph test**, which assesses physiological responses to detect deception, not physical evidence like gunshot residue. - Polygraph tests are not used for identifying **firearm injury** or the presence of actual physical traces. *Toluidine blue test* - The **Toluidine blue test** is primarily used in dentistry to detect and delineate **dysplastic or malignant lesions** in the oral mucosa. - It has no application in the forensic analysis of gunshot residue or firearm use. *Benzidine test for blood stain* - The **Benzidine test** was historically used as a preliminary test for the presence of **blood stains**, as it reacts with the heme component of hemoglobin. - It is not used for detecting **gunshot residue** and has largely been replaced by safer and more specific tests due to its carcinogenic properties.

Question 5: Which of the following statements accurately describes the relationship between quality assurance (QA), quality control (QC), internal quality assurance (IQA), and external quality assurance (EQA)?

A. Quality Control (QC) is a process that supports Quality Assurance (QA).
B. Quality Control (QC) and Quality Assurance (QA) are distinct but interrelated processes.
C. Quality Assurance (QA) focuses solely on compliance and excludes Quality Control (QC).
D. Quality Assurance (QA) includes Quality Control (QC), Internal Quality Assurance (IQA), and External Quality Assurance (EQA). (Correct Answer)

Explanation: ***Quality Assurance (QA) includes Quality Control (QC), Internal Quality Assurance (IQA), and External Quality Assurance (EQA).*** - **Quality Assurance (QA)** is the comprehensive, overarching system that encompasses all systematic activities designed to ensure quality throughout the entire process—from planning and design to implementation and evaluation. - **Quality Control (QC)** is an integral component within QA that focuses on operational techniques and activities used to fulfill quality requirements and detect defects in the final product or service. - **Internal Quality Assurance (IQA)** refers to quality assessment activities conducted within the organization itself (self-assessment, internal audits). - **External Quality Assurance (EQA)** involves quality assessment by external agencies (proficiency testing, external audits, accreditation). - All three (QC, IQA, EQA) function as **components within the broader QA framework**, making this the most comprehensive and accurate description of their relationship. *Quality Control (QC) is a process that supports Quality Assurance (QA).* - While this statement is true, it is incomplete and understates the relationship. - QC is not merely "supportive" but is an **integral operational component** embedded within the QA system. - This option fails to capture the comprehensive hierarchical relationship where QA serves as the umbrella framework encompassing QC, IQA, and EQA. *Quality Control (QC) and Quality Assurance (QA) are distinct but interrelated processes.* - From an operational perspective, QA (proactive, prevention-focused) and QC (reactive, detection-focused) do have distinct roles. - However, in quality management frameworks, QC is best understood as a **functional component within the broader QA system** rather than as a separate parallel process. - This option is less precise than the correct answer, which explicitly describes the inclusive hierarchical relationship. *Quality Assurance (QA) focuses solely on compliance and excludes Quality Control (QC).* - This statement is factually incorrect on both counts. - **QA is not limited to compliance**; it encompasses proactive planning, continuous improvement, systematic monitoring, and excellence in all processes—far beyond mere regulatory compliance. - **QA explicitly includes QC** as a core operational function for monitoring and verifying the quality of outputs, making the claim of exclusion completely wrong.

Question 6: What is the technique for accurate quantification of gene expression?

A. PCR
B. Real-Time Reverse Transcriptase PCR (Correct Answer)
C. Reverse Transcriptase PCR
D. Northern blot

Explanation: ***Real-Time Reverse Transcriptase PCR*** - This technique allows for the **quantification of gene expression** by concurrently reverse-transcribing RNA to cDNA and amplifying it while monitoring the accumulation of DNA in real-time using fluorescent reporters. - The ** threshold cycle (Ct) value** is inversely proportional to the initial amount of target mRNA, enabling precise quantification. *Northern blot* - This method is used to detect **RNA sequences** and can provide semi-quantitative data about gene expression levels based on band intensity. - However, it is generally **less sensitive** and provides less precise quantification compared to real-time PCR. *PCR* - **Standard PCR** amplifies DNA, but it is not directly used for gene expression quantification as it starts with DNA templates. - While it can be used to detect the presence of a gene, it does not quantify its expression without further modifications or additional steps like reverse transcription and real-time monitoring. *Reverse Transcriptase PCR* - This technique involves **reverse transcribing RNA into cDNA** and then performing standard PCR to amplify the cDNA. - While it confirms the presence of mRNA and allows for cDNA amplification, it is a **qualitative or semi-quantitative** method for expression, as the endpoint detection does not accurately reflect initial mRNA concentration due to plateau effects.

Question 7: Which of the following statements about nucleic acid amplification tests (NAATs) for STIs is FALSE?

A. They can be used for test of cure after 3 weeks
B. They can detect dead organisms after treatment
C. They can be used for pharyngeal gonorrhea screening
D. They are less sensitive than culture for rectal chlamydia (Correct Answer)

Explanation: ***They are less sensitive than culture for rectal chlamydia*** - This statement is **FALSE**. NAATs are generally **more sensitive** than culture methods for detecting *Chlamydia trachomatis* in all anatomical sites, including the rectum. - The high sensitivity of NAATs allows for the detection of very low bacterial loads, making them the preferred diagnostic method for many STIs. *They can be used for test of cure after 3 weeks* - This statement is generally **true**. While a "test of cure" (TOC) is not routinely recommended for uncomplicated *Chlamydia* or *Gonorrhea* infections due to high treatment efficacy, it can be considered in specific circumstances (e.g., persistent symptoms, pregnancy, or use of alternative regimens). - If a TOC is performed, it should ideally be done **no sooner than 3 weeks post-treatment** to minimize potential false positives from detecting residual nucleic acids from dead organisms. *They can detect dead organisms after treatment* - This statement is **true**. NAATs detect the **nucleic acids (DNA or RNA)** of the target organism. - These nucleic acids can persist in the body for a period even after the organism has been killed by treatment, leading to a positive NAAT result despite successful eradication of the infection. *They can be used for pharyngeal gonorrhea screening* - This statement is **true**. NAATs are the **recommended method** for detecting *Neisseria gonorrhoeae* in extragenital sites, including the pharynx. - Pharyngeal gonorrhea is often **asymptomatic**, making screening of at-risk individuals important for public health.

Question 8: DNA fingerprinting is used for paternity testing and forensic identification of suspects. Which of the following is the most accurate description of DNA fingerprinting?

A. DNA is isolated from blood, skin, or sperm and its fragment size distribution is analyzed by gel electrophoresis
B. DNA can be isolated from blood, skin, or sperm and analyzed for variable patterns of restriction fragments arising from tandemly repeated sequences (microsatellites) (Correct Answer)
C. DNA is isolated from blood, skin, or sperm and hybridized with probes from the HLA locus to visualize HLA gene patterns
D. DNA is copied from blood, skin, or sperm RNA using reverse transcriptase and analyzed for the pattern of complementary DNAs

Explanation: ***DNA can be isolated from blood, skin, or sperm and analyzed for variable patterns of restriction fragments arising from tandemly repeated sequences (microsatellites)*** - **DNA fingerprinting**, also known as **DNA profiling**, primarily relies on the analysis of highly variable regions of DNA, specifically **tandemly repeated sequences** like microsatellites or STRs (short tandem repeats). - These regions exhibit individual-specific variation in the number of repeats, which, when cut by **restriction enzymes**, produce fragments of varying lengths, generating a unique **restriction fragment length polymorphism (RFLP)** pattern. *DNA is isolated from blood, skin, or sperm and its fragment size distribution is analyzed by gel electrophoresis* - While **gel electrophoresis** is a part of the process to separate DNA fragments by size, this option is incomplete as it doesn't specify *what* fragments are being analyzed or *why* they differ between individuals. - The crucial aspect of DNA fingerprinting is the analysis of **variable short tandem repeats (STRs)** or **variable number tandem repeats (VNTRs)**, which generate these distinct fragment sizes. *DNA is isolated from blood, skin, or sperm and hybridized with probes from the HLA locus to visualize HLA gene patterns* - **HLA (Human Leukocyte Antigen)** typing is used for tissue matching in transplantation and for studying autoimmune diseases, but it is **not the primary method** for DNA fingerprinting in paternity or forensic cases. - While HLA genes are polymorphic, the specific patterns examined in DNA fingerprinting are typically **non-coding repetitive sequences** which are more variable and less complex to interpret for individual identification. *DNA is copied from blood, skin, or sperm RNA using reverse transcriptase and analyzed for the pattern of complementary DNAs* - **DNA fingerprinting** directly analyzes **genomic DNA**, not RNA. The process of reverse transcribing RNA into cDNA is typically used for studying gene expression. - **RNA is less stable** than DNA and does not contain the same highly variable **repetitive sequences** (like STRs or VNTRs) that are fundamental to DNA fingerprinting.

Question 9: DNA fingerprinting can be done with all, except:

A. Saliva
B. WBC
C. RBC (Correct Answer)
D. Spermatozoa

Explanation: ***RBC*** - **Mature red blood cells** lack a nucleus and therefore do not contain **DNA**. - DNA fingerprinting relies on analyzing an individual's unique DNA sequence, which is not present in RBCs. *Saliva* - Saliva contains **epithelial cells** from the mouth, which have intact nuclei and thus sufficient DNA for analysis [2]. - It is a common and non-invasive source of DNA for forensic and genetic testing [2]. *WBC* - **White blood cells** (leukocytes) are nucleated cells that contain a full complement of DNA [2]. - They are an excellent source of DNA for genetic analysis, including DNA fingerprinting. *Spermatozoa* - **Sperm cells** are haploid and contain a nucleus with DNA, making them suitable for DNA fingerprinting [1]. - They are frequently used in forensic cases, particularly in sexual assault investigations [1].

Question 10: Disputed maternity can be solved by using the following tests, EXCEPT:

A. Blood grouping
B. HLA typing
C. DNA fingerprinting
D. Precipitin test (Correct Answer)

Explanation: ***Precipitin test*** - The **precipitin test** is used to determine the origin of a **blood sample**, specifically whether it is **human or animal blood**, by detecting species-specific proteins. It is not used for assessing maternity. - This test is primarily employed in **forensic serology** to differentiate between blood from different animal species, making it irrelevant for paternity or maternity disputes. *Blood grouping* - **Blood grouping** (e.g., ABO and Rh systems) can be used to **exclude paternity or maternity** by comparing the blood types of the child, mother, and alleged father. - If the child's blood type is incompatible with the alleged parents based on Mendelian inheritance, one or both can be excluded. *HLA typing* - **HLA typing** (Human Leukocyte Antigen) is a more powerful genetic marker system than ABO/Rh for determining paternity or maternity. - It involves analyzing highly polymorphic genes on chromosome 6 that encode cell surface proteins, providing a more definitive means of **inclusion or exclusion**. *DNA fingerprinting* - **DNA fingerprinting** (also known as **DNA profiling**) is the **most accurate and widely accepted method** for resolving paternity and maternity disputes. - It analyzes highly variable regions of DNA unique to each individual, providing a statistically strong basis for **inclusion or exclusion** by comparing genetic profiles.

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