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Question 1. Which of the following best describes the primary structural difference between DNA and RNA? A) DNA contains deoxyribose, RNA contains ribose B) DNA is single-stranded, RNA is double-stranded C) DNA uses uracil, RNA uses thymine D) DNA has a phosphate-sugar backbone, RNA does not Answer: A Explanation: The sugar in DNA is deoxyribose (lacking a 2′-OH group), whereas RNA contains ribose (with a 2′-OH), giving RNA greater susceptibility to hydrolysis.
Question 2. In eukaryotic chromatin, which histone is NOT part of the core nucleosome octamer? A) H2A B) H2B C) H D) H Answer: D Explanation: H1 is a linker histone that binds DNA between nucleosomes; the core octamer consists of two copies each of H2A, H2B, H3, and H4.
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Question 3. During DNA replication, which enzyme is responsible for removing RNA primers and filling in the resulting gaps? A) DNA helicase B) DNA polymerase I C) DNA ligase D) Topoisomerase I Answer: B Explanation: In prokaryotes, DNA polymerase I has 5′→3′ exonuclease activity to remove RNA primers and 5′→3′ polymerase activity to replace them with DNA.
Question 4. Which of the following promoter elements is located approximately –10 bp upstream of the transcription start site in bacterial genes? A) TATA box B) CAAT box C) Pribnow box D) Enhancer Answer: C Explanation: The Pribnow (–10) box (TATAAT) is a conserved bacterial promoter element located ~10 bp upstream of the start site, facilitating RNA polymerase binding.
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Question 7. A restriction enzyme that cuts DNA at the sequence 5′-GAATTC- 3 ′ produces which type of ends? A) Blunt ends B) 5′ overhangs (sticky ends) C) 3′ overhangs (sticky ends) D) Single-strand nicks Answer: B Explanation: EcoRI cleaves between G and A, generating 5′ overhangs (sticky ends) of 4 nucleotides (AATT).
Question 8. Which of the following best describes a point mutation that changes a codon from one that codes for an amino acid to a stop codon? A) Silent mutation B) Missense mutation C) Nonsense mutation D) Frameshift mutation Answer: C Explanation: A nonsense mutation introduces a premature termination codon, truncating the protein.
Question 9. In Mendelian inheritance, the term “complete dominance” refers to:
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A) Heterozygotes exhibiting an intermediate phenotype B) One allele completely masking the effect of the other in heterozygotes C) Multiple alleles influencing a single trait D) Traits that are expressed only in homozygotes Answer: B Explanation: Complete dominance occurs when the dominant allele’s phenotype is fully expressed in heterozygotes, masking the recessive allele.
Question 10. Which pre-analytical factor most directly affects the integrity of cell-free DNA in plasma samples? A) Use of EDTA as anticoagulant B) Immediate centrifugation within 2 h of draw C) Storage at –20 °C instead of –80 °C D) Transport at ambient temperature Answer: B Explanation: Prompt centrifugation separates plasma from cellular components, preventing leukocyte lysis that would release genomic DNA and dilute cell-free DNA.
Question 11. During phenol-chloroform extraction, the aqueous phase contains: A) Proteins and lipids
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B) Uracil-N-glycosylase (UNG) with dUTP incorporation C) Heat-inactivation of Taq polymerase D) Adding RNase A to the master mix Answer: B Explanation: Incorporating dUTP into PCR products allows UNG to degrade any contaminating amplicons before the next reaction, preventing false positives.
Question 14. In a nested PCR design, the second (inner) set of primers is intended to: A) Increase the annealing temperature B) Reduce non-specific amplification C) Extend the amplicon length D) Replace the need for a reverse transcriptase Answer: B Explanation: Nested PCR uses two successive amplifications; the inner primers target a region within the first amplicon, enhancing specificity and reducing background.
Question 15. Which real-time PCR detection chemistry uses a fluorophore-quencher pair that is cleaved during extension? A) SYBR Green I
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B) Molecular beacon C) TaqMan probe D) Scorpion probe Answer: C Explanation: TaqMan probes contain a reporter fluorophore and a quencher; the 5′- 3 ′ exonuclease activity of Taq polymerase cleaves the probe during extension, separating fluorophore from quencher and generating signal.
Question 16. The cycle threshold (Cₜ) value in qPCR is inversely related to: A) The initial amount of target nucleic acid B) The efficiency of the polymerase C) The length of the amplicon D) The number of PCR cycles performed Answer: A Explanation: A lower Cₜ indicates a higher starting quantity of target because fewer cycles are required to reach the fluorescence threshold.
Question 17. Loop-mediated isothermal amplification (LAMP) primarily produces: A) Linear single-strand DNA
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B) Fluorescein for direct fluorescence microscopy C) Radioactive ^32P for autoradiography D) Both A and C are common Answer: D Explanation: Southern blots historically used ^32P-labeled probes; modern methods frequently employ non-radioactive labels such as biotin or digoxigenin for chemiluminescence.
Question 20. Sanger sequencing relies on which of the following key components? A) dNTPs only B) dideoxynucleotide triphosphates (ddNTPs) that terminate synthesis C) RNA polymerase for template transcription D) Reverse transcriptase for cDNA synthesis Answer: B Explanation: Incorporation of a ddNTP lacking a 3′-OH halts DNA polymerization, generating fragments of varying lengths that are separated to read the sequence.
Question 21. In next-generation sequencing (NGS), the term “read depth” refers to: A) The length of each sequencing read
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B) The number of times a given nucleotide is sequenced C) The number of samples multiplexed in a run D) The quality score of base calls Answer: B Explanation: Read depth (coverage) indicates how many independent reads cover a particular base, influencing confidence in variant detection.
Question 22. Which microarray technology is primarily used for detecting copy-number variations (CNVs) across the genome? A) cDNA expression array B SNP genotyping array C. Comparative genomic hybridization (aCGH) array D. Protein-binding microarray Answer: C Explanation: Array CGH compares fluorescently labeled test and reference DNA to identify gains or losses of genomic regions, revealing CNVs.
Question 23. MALDI-TOF mass spectrometry is most frequently employed in clinical microbiology for: A) Quantifying viral load B) Identifying bacterial species based on protein fingerprints
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C) HIV viral load by RT-qPCR D. Western blot for HIV proteins Answer: C Explanation: HIV viral load measurement uses reverse transcription quantitative PCR to determine the number of RNA copies per milliliter, guiding treatment decisions.
Question 26. KRAS exon 2 mutations (G12D, G12V) are most relevant in which clinical context? A) Predicting response to EGFR inhibitors in colorectal cancer B) Determining eligibility for BCR-ABL1 tyrosine-kinase inhibitors C) Guiding therapy for chronic myeloid leukemia D) Assessing risk of hereditary breast-ovarian cancer Answer: A Explanation: KRAS mutations downstream of EGFR confer resistance to anti-EGFR monoclonal antibodies (e.g., cetuximab) in metastatic colorectal cancer.
Question 27. The most common mutation tested in Factor V Leiden thrombophilia involves a single-base substitution at nucleotide 1691 (G→A). This mutation results in: A) An amino-acid change from Arg to Gln
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B) A premature stop codon C) A splice-site alteration D) A silent mutation Answer: A Explanation: The G1691A change converts Arg506 to Gln, impairing protein C cleavage and increasing clotting risk.
Question 28. In forensic DNA analysis, the CODIS core loci primarily consist of: A) Mitochondrial DNA hypervariable regions B) Short tandem repeats (STRs) on autosomes C) Single-nucleotide polymorphisms (SNPs) on the Y chromosome D) Copy-number variations in the genome Answer: B Explanation: CODIS uses a panel of autosomal STR markers because they are highly polymorphic, easy to amplify, and have low mutation rates.
Question 29. Warfarin dosing is affected most significantly by polymorphisms in which gene? A) CYP2C B) VKORC
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D) At room temperature Answer: B Explanation: Annealing temperature is usually 3–5 °C below the primer Tm to allow stable hybridization without nonspecific binding.
Question 32. Which of the following reagents is most commonly used to inactivate RNases during RNA extraction? A) Proteinase K B) RNase inhibitor (RNasin) C) SDS D) Phenol Answer: B Explanation: RNase inhibitors bind and block RNase activity, preserving RNA integrity throughout extraction and downstream applications.
Question 33. In a multiplex PCR assay detecting three respiratory viruses, what is the primary challenge to be addressed? A) Ensuring all primers have identical Tm values B) Using a single fluorescent probe for all targets C) Performing the reaction at a lower annealing temperature than standard PCR D) Avoiding primer-dimer formation among multiple primer sets
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Answer: D Explanation: Multiplex PCR involves many primers; careful design is required to minimize cross-reactivity and primer-dimers that can reduce assay sensitivity.
Question 34. Which of the following best explains why a nonsense- mediated decay (NMD) pathway exists in eukaryotic cells? A) To enhance transcription of mutant genes B) To degrade mRNAs containing premature stop codons C) To increase translation efficiency of all mRNAs D) To promote alternative splicing Answer: B Explanation: NMD surveils mRNA and eliminates transcripts with premature termination codons, preventing production of truncated, potentially deleterious proteins.
Question 35. A laboratory implements a “no-template control” (NTC) in every PCR run. The purpose of the NTC is to: A) Verify the efficiency of the polymerase B) Detect contamination of reagents with target DNA C) Quantify the amount of target in the sample D) Serve as a positive amplification reference
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Answer: B Explanation: Library preparation fragments DNA (or cDNA) and ligates adapters that enable clonal amplification and sequencing on the chosen platform.
Question 38. Which of the following quality-control metrics is most appropriate for assessing the performance of a real-time PCR assay? A) A260/A280 ratio of extracted nucleic acid B) Amplification efficiency (E) close to 100% C) Gel electrophoresis band intensity D) Number of cycles in the denaturation step Answer: B Explanation: Amplification efficiency, derived from the slope of the standard curve, indicates how well the assay doubles target each cycle; values between 90–110% are acceptable.
Question 39. The CLIA “high-complexity” classification for a molecular assay is primarily based on: A) The cost of the instrument used B) The level of training required to interpret results C) The number of samples processed per day D) Whether the assay uses fluorescent detection
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Answer: B Explanation: High-complexity tests demand extensive technical knowledge, interpretation, and quality-control procedures, distinguishing them from moderate- and waived-complexity tests.
Question 40. A laboratory technician notices a faint band at the expected size on an agarose gel after a PCR that included a high-GC template. Which modification is most likely to improve amplification? A) Increase the annealing temperature by 10 °C B) Add DMSO or betaine to the reaction mix C) Reduce the extension time to 15 s D) Use a lower concentration of MgCl₂ Answer: B Explanation: DMSO or betaine reduces secondary structure in GC-rich templates, enhancing primer annealing and polymerase progression.
Question 41. Which of the following is a characteristic feature of a “silent” mutation? A) Alters the amino-acid sequence B) Introduces a premature stop codon C) Does not change the encoded amino acid due to codon redundancy D) Shifts the reading frame
