Q.1 What does DNA stand for?
Deoxyribonucleic Acid
Deoxy Ribose Acid
Dioxyribose Nucleic Acid
Deoxy Nitrogen Acid
Explanation - DNA is the abbreviation for Deoxyribonucleic Acid, the molecule that carries genetic information.
Correct answer is: Deoxyribonucleic Acid
Q.2 Which of the following is the basic structural unit of DNA?
Amino acid
Nucleotide
Lipid
Polysaccharide
Explanation - DNA is composed of repeating units called nucleotides, each containing a sugar, a phosphate group, and a nitrogenous base.
Correct answer is: Nucleotide
Q.3 Which pair correctly represents complementary DNA bases?
Adenine‑Thymine, Cytosine‑Guanine
Adenine‑Guanine, Cytosine‑Thymine
Adenine‑Cytosine, Thymine‑Guanine
Adenine‑Uracil, Cytosine‑Guanine
Explanation - In DNA, adenine pairs with thymine (A‑T) and cytosine pairs with guanine (C‑G) via hydrogen bonds.
Correct answer is: Adenine‑Thymine, Cytosine‑Guanine
Q.4 The sugar component of DNA is:
Ribose
Deoxyribose
Glucose
Fructose
Explanation - DNA contains the five‑carbon sugar deoxyribose, which lacks an oxygen atom at the 2' position compared with ribose.
Correct answer is: Deoxyribose
Q.5 What is the shape of the DNA molecule?
Triple helix
Double helix
Single strand
Quadruple helix
Explanation - Watson and Crick described DNA as a right‑handed double helix formed by two antiparallel strands.
Correct answer is: Double helix
Q.6 Which enzyme synthesizes a new DNA strand during replication?
RNA polymerase
DNA helicase
DNA ligase
DNA polymerase
Explanation - DNA polymerase adds nucleotides to a growing DNA chain using a template strand during replication.
Correct answer is: DNA polymerase
Q.7 During DNA replication, which of the following creates the replication fork?
DNA polymerase
DNA ligase
DNA helicase
Topoisomerase
Explanation - DNA helicase unwinds the double helix, producing two single‑stranded templates and the replication fork.
Correct answer is: DNA helicase
Q.8 What is the purpose of the enzyme DNA ligase?
Unwinds DNA strands
Adds nucleotides to a growing strand
Joins Okazaki fragments
Proofreads DNA
Explanation - DNA ligase catalyzes the formation of phosphodiester bonds between adjacent DNA fragments, especially on the lagging strand.
Correct answer is: Joins Okazaki fragments
Q.9 In a PCR reaction, which temperature step allows primers to anneal to the template DNA?
Denaturation (≈95 °C)
Annealing (≈55‑65 °C)
Extension (≈72 °C)
Cooling (≈4 °C)
Explanation - During annealing, temperature is lowered so short primers can hybridize to their complementary sequences on the template.
Correct answer is: Annealing (≈55‑65 °C)
Q.10 Which component of the PCR mix provides the building blocks for new DNA strands?
DNA polymerase
Primers
dNTPs
Buffer solution
Explanation - Deoxynucleotide triphosphates (dNTPs) are the substrates that DNA polymerase incorporates into the new DNA strand.
Correct answer is: dNTPs
Q.11 What is the main difference between DNA and RNA?
DNA contains uracil, RNA contains thymine
DNA is single‑stranded, RNA is double‑stranded
DNA contains deoxyribose, RNA contains ribose
DNA uses A‑U base pairing, RNA uses A‑T
Explanation - DNA's sugar is deoxyribose, lacking an OH at the 2' carbon, while RNA contains ribose with a hydroxyl group at that position.
Correct answer is: DNA contains deoxyribose, RNA contains ribose
Q.12 Which technique is used to determine the order of nucleotides in a DNA fragment?
Western blot
Sanger sequencing
ELISA
Northern blot
Explanation - Sanger (chain‑termination) sequencing uses dideoxynucleotides to generate DNA fragments of varying lengths for base calling.
Correct answer is: Sanger sequencing
Q.13 In CRISPR‑Cas9 gene editing, what role does the guide RNA (gRNA) play?
Cuts the DNA backbone
Provides a template for repair
Directs Cas9 to a specific DNA sequence
Activates transcription of target genes
Explanation - The gRNA contains a 20‑nt sequence complementary to the target DNA, guiding Cas9 endonuclease to the precise location for cleavage.
Correct answer is: Directs Cas9 to a specific DNA sequence
Q.14 Which DNA repair mechanism corrects mismatched bases after replication?
Nucleotide excision repair
Base excision repair
Mismatch repair
Homologous recombination
Explanation - Mismatch repair proteins recognize and excise incorrectly paired bases, then DNA polymerase fills the gap using the correct strand as template.
Correct answer is: Mismatch repair
Q.15 What is the function of telomerase in eukaryotic cells?
Separates sister chromatids
Synthesizes ribosomal RNA
Adds repetitive sequences to chromosome ends
Degrades damaged DNA
Explanation - Telomerase extends telomeres by adding TTAGGG repeats, preventing chromosome shortening during replication.
Correct answer is: Adds repetitive sequences to chromosome ends
Q.16 Which of the following statements about plasmids is FALSE?
They can replicate independently of chromosomal DNA.
They are typically circular DNA molecules.
They can carry antibiotic‑resistance genes.
They are transcribed by RNA polymerase II.
Explanation - Plasmids are prokaryotic elements; transcription uses bacterial RNA polymerase, not eukaryotic RNA polymerase II.
Correct answer is: They are transcribed by RNA polymerase II.
Q.17 In gel electrophoresis, DNA fragments are separated primarily based on:
Charge density
Molecular weight
Shape
Hydrophobicity
Explanation - DNA fragments have uniform negative charge per base, so separation in an agarose gel occurs mainly due to size (molecular weight).
Correct answer is: Molecular weight
Q.18 Which enzyme creates nicks in the DNA backbone during the initiation of DNA replication?
DNA polymerase I
RNA primase
DNA helicase
DNA ligase
Explanation - Primase synthesizes a short RNA primer, forming a 3'‑OH that DNA polymerase can extend from, effectively creating a nicked start point.
Correct answer is: RNA primase
Q.19 What is the main advantage of using a high‑fidelity DNA polymerase in PCR?
Higher speed of amplification
Lower error rate during DNA synthesis
Ability to amplify longer fragments
Reduced need for primers
Explanation - High‑fidelity polymerases possess proofreading activity, decreasing incorporation of incorrect nucleotides.
Correct answer is: Lower error rate during DNA synthesis
Q.20 Which of the following best describes a “silent mutation” in DNA?
A change that introduces a premature stop codon
A substitution that does not alter the encoded amino acid
A deletion that shifts the reading frame
An insertion that creates a new start codon
Explanation - Due to the redundancy of the genetic code, some base changes do not affect the resulting protein sequence.
Correct answer is: A substitution that does not alter the encoded amino acid
Q.21 In the context of DNA sequencing, what does “coverage” refer to?
The number of different species sequenced in a study
The proportion of the genome that is sequenced at least once
The depth of sequencing, i.e., average number of reads per base
The length of the reads generated by the sequencer
Explanation - Coverage (or depth) indicates how many times each nucleotide is read, influencing accuracy of the final sequence.
Correct answer is: The depth of sequencing, i.e., average number of reads per base
Q.22 Which of the following best explains why DNA is negatively charged?
The phosphate groups contain a negative charge at physiological pH
The nitrogenous bases are anionic
The deoxyribose sugar has a carboxyl group
Hydrogen bonds impart negative charge
Explanation - Each phosphate backbone carries a negative charge due to its ionized phosphoric acid groups.
Correct answer is: The phosphate groups contain a negative charge at physiological pH
Q.23 What is the purpose of a “restriction enzyme” in recombinant DNA technology?
To amplify DNA fragments
To join DNA fragments together
To cut DNA at specific sequences
To transcribe DNA into RNA
Explanation - Restriction endonucleases recognize short palindromic sequences and cleave DNA, generating compatible ends for cloning.
Correct answer is: To cut DNA at specific sequences
Q.24 Which of the following statements about the genetic code is FALSE?
It is universal across almost all organisms.
It is degenerate, meaning multiple codons can encode the same amino acid.
It is ambiguous; a single codon can specify more than one amino acid.
It is read in a non‑overlapping, triplet manner.
Explanation - The genetic code is unambiguous: each codon specifies exactly one amino acid (or a stop signal).
Correct answer is: It is ambiguous; a single codon can specify more than one amino acid.
Q.25 During transcription, which enzyme synthesizes the RNA strand?
DNA polymerase
RNA polymerase
DNA ligase
RNA ligase
Explanation - RNA polymerase reads the DNA template and polymerizes ribonucleotides into a complementary RNA molecule.
Correct answer is: RNA polymerase
Q.26 Which of the following is a common method to introduce foreign DNA into bacterial cells?
Electroporation
Centrifugation
Spectrophotometry
Chromatography
Explanation - Electroporation applies an electric field to create temporary pores in the cell membrane, allowing DNA uptake.
Correct answer is: Electroporation
Q.27 What is the main function of a promoter region in a gene?
Encode a protein domain
Terminate transcription
Bind RNA polymerase to initiate transcription
Serve as a ribosome binding site
Explanation - Promoters contain specific sequences that recruit RNA polymerase and transcription factors to start RNA synthesis.
Correct answer is: Bind RNA polymerase to initiate transcription
Q.28 In a DNA double helix, the two strands run in opposite directions. This orientation is called:
Parallel
Antiparallel
Co‑linear
Symmetric
Explanation - One strand runs 5'→3' while the complementary strand runs 3'→5', giving the antiparallel arrangement.
Correct answer is: Antiparallel
Q.29 Which type of RNA carries the genetic code from DNA to the ribosome?
tRNA
rRNA
mRNA
snRNA
Explanation - Messenger RNA (mRNA) is transcribed from DNA and conveys the coding sequence to the ribosome for translation.
Correct answer is: mRNA
Q.30 What is a “primer” in the context of PCR?
A short DNA fragment that initiates synthesis
An enzyme that degrades DNA
A fluorescent dye for detection
A buffer component
Explanation - Primers are synthetic oligonucleotides that bind to specific target sequences, providing a 3'‑OH for DNA polymerase.
Correct answer is: A short DNA fragment that initiates synthesis
Q.31 Which of the following best describes a “point mutation”?
Insertion of a large DNA segment
Deletion of an entire gene
Change of a single nucleotide
Duplication of a chromosome
Explanation - Point mutations involve substitution, insertion, or deletion of a single base pair in the DNA sequence.
Correct answer is: Change of a single nucleotide
Q.32 The “central dogma” of molecular biology states that:
DNA → RNA → Protein
RNA → DNA → Protein
Protein → DNA → RNA
DNA ↔ Protein ↔ RNA
Explanation - Genetic information flows from DNA to RNA (transcription) and then to protein (translation).
Correct answer is: DNA → RNA → Protein
Q.33 Which of the following is NOT a typical use of CRISPR‑Cas systems?
Gene knockout
Base editing without double‑strand breaks
Protein purification
Gene activation (CRISPRa)
Explanation - CRISPR is a genome‑editing tool; protein purification relies on different biochemical methods.
Correct answer is: Protein purification
Q.34 In DNA sequencing by synthesis (e.g., Illumina), what role do fluorescently labelled nucleotides play?
They stop DNA polymerase activity
They enable detection of incorporated bases via imaging
They increase the speed of polymerization
They degrade the template strand
Explanation - Each incorporated labeled nucleotide emits a specific fluorescence, allowing the sequencer to identify the base added at each cycle.
Correct answer is: They enable detection of incorporated bases via imaging
Q.35 What is the main function of the “origin of replication” in a plasmid?
To encode antibiotic resistance
To initiate transcription of plasmid genes
To serve as the site where DNA replication begins
To bind transcription factors
Explanation - The origin of replication (ori) is a specific sequence recognized by replication proteins to start copying the plasmid.
Correct answer is: To serve as the site where DNA replication begins
Q.36 Which of the following best describes “homologous recombination” in DNA repair?
Joining of non‑matching DNA ends
Exchange of DNA between identical or similar sequences
Cutting DNA at restriction sites
Direct ligation without a template
Explanation - Homologous recombination uses a homologous template to accurately repair double‑strand breaks.
Correct answer is: Exchange of DNA between identical or similar sequences
Q.37 The presence of which base in RNA distinguishes it from DNA?
Adenine
Guanine
Cytosine
Uracil
Explanation - RNA contains uracil (U) instead of thymine (T) found in DNA.
Correct answer is: Uracil
Q.38 In a Southern blot, DNA fragments are transferred onto a membrane and then detected using:
Antibodies
Radioactively or fluorescently labeled probes
Enzyme substrates
Lipids
Explanation - Probes complementary to the target sequence hybridize to the membrane‑bound DNA, allowing visualization.
Correct answer is: Radioactively or fluorescently labeled probes
Q.39 Which of the following best explains why DNA replication is considered semi‑conservative?
Both daughter strands are newly synthesized
Each daughter DNA contains one original and one new strand
The parental DNA is completely degraded
New DNA is synthesized without any template
Explanation - Semi‑conservative replication produces two DNA molecules, each composed of one parental and one newly synthesized strand.
Correct answer is: Each daughter DNA contains one original and one new strand
Q.40 What is the purpose of a “multiple cloning site (MCS)” in a plasmid vector?
To increase plasmid copy number
To provide a region with many restriction sites for insertion of foreign DNA
To encode a fluorescent protein
To serve as a transcription terminator
Explanation - An MCS contains several unique restriction sites, facilitating easy cloning of DNA fragments.
Correct answer is: To provide a region with many restriction sites for insertion of foreign DNA
Q.41 Which of the following enzymes is used to remove RNA primers during DNA replication in prokaryotes?
DNA polymerase I
DNA ligase
RNA polymerase
Topoisomerase
Explanation - DNA polymerase I has 5'→3' exonuclease activity that removes RNA primers and fills in the gaps with DNA.
Correct answer is: DNA polymerase I
Q.42 In the context of gene expression, what does the term “inducible promoter” refer to?
A promoter that is always active
A promoter that can be turned on by a specific signal or molecule
A promoter that drives constitutive high‑level expression
A promoter that silences gene transcription
Explanation - Inducible promoters respond to environmental or chemical cues, allowing controlled gene expression.
Correct answer is: A promoter that can be turned on by a specific signal or molecule
Q.43 Which of the following best describes the principle behind the “DNA microarray” technology?
Sequencing DNA fragments one by one
Amplifying DNA using PCR
Hybridizing labeled cDNA to thousands of DNA probes on a chip to measure gene expression
Separating DNA fragments by size on a gel
Explanation - Microarrays contain immobilized probes; hybridization intensity reflects the abundance of specific transcripts.
Correct answer is: Hybridizing labeled cDNA to thousands of DNA probes on a chip to measure gene expression
Q.44 What is the main limitation of Sanger sequencing compared with next‑generation sequencing (NGS) technologies?
Higher error rate
Inability to read RNA
Low throughput and high cost per base
Requires fluorescent labels
Explanation - Sanger sequencing reads one fragment at a time, making it slower and more expensive for large genomes than NGS.
Correct answer is: Low throughput and high cost per base
Q.45 Which of the following is NOT a typical feature of a eukaryotic promoter?
TATA box
CAAT box
Kozak sequence
Pribnow box
Explanation - The Pribnow box is a prokaryotic -10 promoter element; eukaryotes have TATA and CAAT boxes, while the Kozak sequence is part of translation initiation.
Correct answer is: Pribnow box
Q.46 During DNA replication, the leading strand is synthesized:
Continuously in the 5'→3' direction
Discontinuously in short fragments
In the 3'→5' direction
Only after the lagging strand
Explanation - The leading strand follows the replication fork and can be synthesized continuously by DNA polymerase.
Correct answer is: Continuously in the 5'→3' direction
Q.47 Which of the following best describes “base excision repair (BER)”?
Removal of bulky DNA adducts
Repair of single‑base lesions via a glycosylase and DNA polymerase
Fixing double‑strand breaks using a sister chromatid
Correcting mismatched bases after replication
Explanation - BER involves removal of a damaged base by a DNA glycosylase, followed by end processing, gap filling, and ligation.
Correct answer is: Repair of single‑base lesions via a glycosylase and DNA polymerase
Q.48 In the context of gene therapy, what does the term “viral vector” refer to?
A synthetic nanoparticle used to deliver drugs
A virus that has been engineered to carry therapeutic DNA
A plasmid that replicates independently in human cells
A peptide that facilitates cell entry
Explanation - Viral vectors exploit the natural ability of viruses to enter cells, delivering corrective genetic material without causing disease.
Correct answer is: A virus that has been engineered to carry therapeutic DNA
Q.49 Which of the following techniques can be used to quantify the amount of a specific DNA sequence in a sample?
Northern blot
Southern blot
qPCR (quantitative PCR)
Western blot
Explanation - qPCR monitors fluorescence during amplification, providing real‑time quantification of target DNA.
Correct answer is: qPCR (quantitative PCR)
Q.50 The “Watson‑Crick base pairing rule” is based on:
Hydrogen bonding and molecular shape complementarity
Covalent bonding between bases
Ionic interactions
Van der Waals forces only
Explanation - A‑T pairs via two hydrogen bonds; G‑C pairs via three hydrogen bonds, fitting together due to complementary shapes.
Correct answer is: Hydrogen bonding and molecular shape complementarity
Q.51 What is the function of the 5' cap added to eukaryotic mRNA?
Facilitates nuclear export and protects mRNA from degradation
Marks the start codon for translation
Signals termination of transcription
Serves as a binding site for DNA polymerase
Explanation - The 7‑methylguanosine cap protects mRNA, aids ribosome binding, and is required for transport to the cytoplasm.
Correct answer is: Facilitates nuclear export and protects mRNA from degradation
Q.52 Which of the following best describes a “knock‑in” mouse model?
A mouse where a gene has been completely deleted
A mouse carrying a transgene inserted at a random genomic location
A mouse where a specific gene mutation has been introduced at its native locus
A mouse that overexpresses a viral protein
Explanation - Knock‑in models insert or replace DNA precisely at the endogenous gene location, preserving regulatory context.
Correct answer is: A mouse where a specific gene mutation has been introduced at its native locus
Q.53 In the context of DNA manipulation, what does the term “blunt‑end ligation” refer to?
Joining of DNA fragments with overhanging sticky ends
Joining of DNA fragments with no overhangs
Insertion of a restriction site
Removal of phosphate groups from DNA ends
Explanation - Blunt‑end ligation involves ligating DNA ends that are straight cut, lacking single‑strand overhangs.
Correct answer is: Joining of DNA fragments with no overhangs
Q.54 Which of the following best explains why GC‑rich regions of DNA have higher melting temperatures?
GC pairs have three hydrogen bonds compared to two in AT pairs
GC bases are larger and block heat flow
GC regions contain more phosphates
GC sequences bind more tightly to proteins
Explanation - The extra hydrogen bond in G‑C pairs stabilizes the double helix, raising the temperature required to denature it.
Correct answer is: GC pairs have three hydrogen bonds compared to two in AT pairs
Q.55 Which enzyme is primarily responsible for repairing UV‑induced pyrimidine dimers in DNA?
DNA polymerase I
DNA photolyase
DNA ligase
RNA polymerase
Explanation - Photolyase uses visible light energy to cleave cyclobutane pyrimidine dimers formed by UV exposure.
Correct answer is: DNA photolyase
Q.56 What is the main purpose of the “poly‑A tail” added to eukaryotic mRNA?
To aid in splicing of introns
To increase mRNA stability and assist in translation initiation
To serve as a signal for nuclear export
To encode the start codon
Explanation - The poly‑A tail protects mRNA from exonucleases and interacts with translation factors.
Correct answer is: To increase mRNA stability and assist in translation initiation
Q.57 Which of the following best describes the role of “RNA interference (RNAi)” in gene regulation?
It increases transcription of target genes
It degrades specific mRNA molecules, reducing protein synthesis
It modifies DNA methylation patterns
It promotes DNA replication
Explanation - RNAi utilizes small RNAs (siRNA, miRNA) to target complementary mRNAs for cleavage or translational repression.
Correct answer is: It degrades specific mRNA molecules, reducing protein synthesis
Q.58 In a typical agarose gel electrophoresis setup, why is the DNA sample loaded near the negative (cathode) side?
DNA is negatively charged and moves toward the positive (anode) electrode
DNA is positively charged and moves toward the negative electrode
The gel matrix repels DNA toward the cathode
Loading near the cathode prevents overheating
Explanation - DNA's phosphate backbone carries negative charge; it migrates towards the anode under an electric field.
Correct answer is: DNA is negatively charged and moves toward the positive (anode) electrode
Q.59 Which of the following statements about “epigenetic modifications” is TRUE?
They alter the DNA nucleotide sequence
They are always permanent and irreversible
They can affect gene expression without changing the DNA sequence
They only occur in prokaryotes
Explanation - Epigenetic changes such as DNA methylation and histone modifications regulate transcription without altering the underlying sequence.
Correct answer is: They can affect gene expression without changing the DNA sequence
Q.60 Which of the following enzymes is essential for the ligation of DNA fragments with cohesive (sticky) ends?
DNA polymerase
DNA ligase
RNA polymerase
Topoisomerase
Explanation - DNA ligase catalyzes phosphodiester bond formation between adjacent nucleotides, sealing nicks in the backbone.
Correct answer is: DNA ligase
Q.61 What does the term “synthetic biology” encompass?
The study of ancient fossils
Designing and constructing new biological parts, devices, and systems
Only the sequencing of genomes
Analyzing ecological interactions
Explanation - Synthetic biology combines engineering principles with biology to create novel biological functions and systems.
Correct answer is: Designing and constructing new biological parts, devices, and systems
Q.62 In the context of next‑generation sequencing, what does the term “read length” refer to?
The total number of reads generated
The number of nucleotides sequenced in a single continuous stretch
The speed of the sequencing run
The physical length of the flow cell
Explanation - Read length is the length of each individual DNA fragment that is sequenced in one pass.
Correct answer is: The number of nucleotides sequenced in a single continuous stretch
Q.63 Which of the following best describes “gene silencing” by DNA methylation?
Addition of methyl groups to adenine bases in RNA
Methylation of cytosine residues in CpG islands leading to transcriptional repression
Phosphorylation of histone tails
Acetylation of DNA backbone
Explanation - DNA methyltransferases add methyl groups to cytosines in CpG dinucleotides, often silencing gene expression.
Correct answer is: Methylation of cytosine residues in CpG islands leading to transcriptional repression
Q.64 The “Klenow fragment” of DNA polymerase I lacks which activity?
5'→3' polymerase activity
3'→5' exonuclease (proofreading) activity
5'→3' exonuclease activity
DNA ligase activity
Explanation - The Klenow fragment retains polymerase and 3'→5' exonuclease functions but lacks the 5'→3' exonuclease activity of the full enzyme.
Correct answer is: 5'→3' exonuclease activity
Q.65 Which of the following best explains why “high‑GC content” genomes are more challenging to amplify by PCR?
GC pairs form stronger hydrogen bonds, requiring higher denaturation temperatures
GC bases inhibit DNA polymerase binding
GC-rich regions attract nucleases
GC content reduces primer annealing efficiency
Explanation - Three hydrogen bonds in G‑C pairs increase melting temperature, making strand separation harder during PCR cycles.
Correct answer is: GC pairs form stronger hydrogen bonds, requiring higher denaturation temperatures
Q.66 In the context of DNA nanotechnology, a “DNA origami” structure is built by:
Randomly folding DNA strands
Using a long scaffold strand and many short staple strands to create a predefined shape
Enzymatically ligating random fragments
Synthesizing DNA in a solid‑phase reactor
Explanation - DNA origami uses a single long strand folded into a shape by numerous short, complementary staple strands.
Correct answer is: Using a long scaffold strand and many short staple strands to create a predefined shape
Q.67 Which of the following best describes the purpose of a “reporter gene” in a genetic construct?
To provide antibiotic resistance
To encode a protein that can be easily measured, indicating expression of the construct
To serve as a replication origin
To inhibit host cell division
Explanation - Reporter genes (e.g., GFP, luciferase) produce detectable signals that reflect transcriptional activity of the construct.
Correct answer is: To encode a protein that can be easily measured, indicating expression of the construct
Q.68 What is the primary advantage of using “digital PCR” over traditional qPCR?
It does not require primers
It provides absolute quantification without standard curves
It can amplify RNA directly
It uses fluorescent dyes only
Explanation - Digital PCR partitions the sample into many micro‑reactions, allowing direct counting of positive versus negative partitions for absolute quantification.
Correct answer is: It provides absolute quantification without standard curves
Q.69 Which of the following is a key component of the CRISPR‑Cas12 system that distinguishes it from Cas9?
Cas12 creates a single‑strand nick
Cas12 can cleave single‑stranded DNA in a collateral manner
Cas12 does not require a guide RNA
Cas12 works only in prokaryotes
Explanation - Cas12 exhibits trans‑cleavage activity on non‑target single‑stranded DNA after activation, useful for diagnostic assays.
Correct answer is: Cas12 can cleave single‑stranded DNA in a collateral manner
Q.70 In the context of genome assembly, a “contig” is:
A single DNA fragment that cannot be assembled
A set of overlapping DNA sequences that have been merged into a continuous stretch
A protein complex that binds DNA
A type of restriction enzyme
Explanation - Contigs represent assembled, contiguous sequences derived from overlapping reads.
Correct answer is: A set of overlapping DNA sequences that have been merged into a continuous stretch
Q.71 Which technique would you use to specifically edit a single nucleotide without creating double‑strand breaks?
CRISPR‑Cas9 nuclease
Base editing using a deaminase‑fused dead Cas9 (dCas9)
RNA interference
Zinc‑finger nuclease
Explanation - Base editors convert one base to another directly, avoiding double‑strand cleavage.
Correct answer is: Base editing using a deaminase‑fused dead Cas9 (dCas9)
Q.72 What is the main function of the “ribosome binding site (RBS)” in prokaryotic mRNA?
Signal transcription termination
Recruit RNA polymerase
Facilitate ribosome attachment for translation initiation
Encode a peptide
Explanation - The RBS (Shine‑Dalgarno sequence) pairs with the 16S rRNA to position the ribosome at the start codon.
Correct answer is: Facilitate ribosome attachment for translation initiation
Q.73 Which of the following best explains why “DNA sequencing” is essential for personalized medicine?
It allows the design of universal drugs for all patients
It enables identification of individual genetic variants that influence disease risk and drug response
It replaces the need for clinical trials
It provides information about a patient’s diet
Explanation - Sequencing reveals mutations and polymorphisms that guide tailored therapeutic strategies.
Correct answer is: It enables identification of individual genetic variants that influence disease risk and drug response
Q.74 In a “nested PCR” protocol, why are two sets of primers used?
To amplify two different genes simultaneously
To increase specificity by re‑amplifying a product from the first PCR with internal primers
To reduce the number of cycles needed
To add fluorescent labels in the second round
Explanation - Nested PCR reduces non‑specific amplification by using inner primers that bind within the first amplicon.
Correct answer is: To increase specificity by re‑amplifying a product from the first PCR with internal primers
Q.75 Which of the following is a characteristic of “RNA‑Seq” compared with microarrays?
RNA‑Seq can detect novel transcripts and splice variants
RNA‑Seq requires pre‑designed probes
Microarrays have higher dynamic range than RNA‑Seq
RNA‑Seq cannot quantify low‑abundance transcripts
Explanation - RNA‑Seq provides unbiased, sequence‑based profiling, enabling discovery of new transcripts and isoforms.
Correct answer is: RNA‑Seq can detect novel transcripts and splice variants
Q.76 What does the acronym “qRT‑PCR” stand for, and what does it measure?
quantitative rapid‑temperature PCR; measures DNA melting temperature
quantitative reverse‑transcription PCR; measures the amount of specific RNA transcripts
quick RNA‑template PCR; measures RNA synthesis rate
qualitative replication‑target PCR; measures DNA replication fidelity
Explanation - qRT‑PCR first converts RNA to cDNA (reverse transcription) and then quantitatively amplifies it in real time.
Correct answer is: quantitative reverse‑transcription PCR; measures the amount of specific RNA transcripts
Q.77 Which of the following best describes the purpose of a “selection marker” in a cloning vector?
To increase plasmid copy number
To enable growth of only those cells that have taken up the vector
To promote transcription of the inserted gene
To degrade unwanted DNA
Explanation - Selection markers (e.g., antibiotic resistance genes) allow identification of transformed cells on selective media.
Correct answer is: To enable growth of only those cells that have taken up the vector
Q.78 In the context of DNA replication, the “Okazaki fragments” are synthesized on the:
Leading strand
Lagging strand
Both strands simultaneously
Only in mitochondrial DNA
Explanation - Okazaki fragments are short DNA pieces formed discontinuously on the lagging strand, later joined by DNA ligase.
Correct answer is: Lagging strand
Q.79 Which of the following statements about “synthetic promoters” is correct?
They are natural promoters isolated from bacteria
They are engineered sequences designed to achieve desired levels of transcription
They cannot be used in eukaryotic cells
They always contain a TATA box
Explanation - Synthetic promoters are designed by combining or mutating regulatory elements to fine‑tune gene expression.
Correct answer is: They are engineered sequences designed to achieve desired levels of transcription
Q.80 What is the primary purpose of a “DNA fingerprint” (or STR profiling) in forensic science?
To determine an individual's blood type
To compare the number of repeats at specific microsatellite loci for identity matching
To sequence the entire genome
To measure gene expression levels
Explanation - Short tandem repeat (STR) analysis examines polymorphic repeat numbers, providing a unique genetic profile.
Correct answer is: To compare the number of repeats at specific microsatellite loci for identity matching
Q.81 Which of the following is a characteristic of “non‑homologous end joining (NHEJ)” DNA repair?
Requires a homologous template
Often introduces small insertions or deletions at the repair site
Only occurs during S phase
Never leads to mutations
Explanation - NHEJ ligates broken DNA ends directly and can be error‑prone, resulting in indels.
Correct answer is: Often introduces small insertions or deletions at the repair site
Q.82 Which of the following best describes “synthetic lethal screening” in cancer genetics?
Identifying gene pairs where loss of both leads to cell death, while loss of one is tolerated
Finding genes that increase drug resistance
Sequencing tumor DNA for mutations
Measuring tumor size after chemotherapy
Explanation - Synthetic lethality exploits vulnerabilities in cancer cells by targeting genes that become essential only when another is mutated.
Correct answer is: Identifying gene pairs where loss of both leads to cell death, while loss of one is tolerated
Q.83 In a typical cloning workflow, why is a “dephosphorylation step” often performed on the vector after restriction digestion?
To prevent the vector from self‑ligating
To increase the efficiency of restriction enzyme cutting
To label the vector with fluorescent dye
To enhance transformation efficiency
Explanation - Removing 5' phosphates from the linearized vector blocks ligation of the vector to itself, favoring insertion of the insert.
Correct answer is: To prevent the vector from self‑ligating
Q.84 Which of the following best explains why “reverse transcription‑PCR (RT‑PCR)” is used to detect RNA viruses?
RNA viruses lack DNA, so their genomes must be converted to cDNA before PCR amplification
RT‑PCR can amplify DNA directly without conversion
RNA viruses are resistant to standard PCR enzymes
RT‑PCR measures protein levels of the virus
Explanation - Reverse transcriptase synthesizes complementary DNA (cDNA) from the viral RNA, which can then be amplified by PCR.
Correct answer is: RNA viruses lack DNA, so their genomes must be converted to cDNA before PCR amplification
Q.85 What is the main advantage of using “phage display” in protein engineering?
It allows rapid screening of large peptide libraries for binding to a target
It integrates DNA into the host genome permanently
It increases the mutation rate of a gene
It provides high‑resolution structural data
Explanation - Phage display presents peptides on the surface of bacteriophages, enabling selection of high‑affinity binders from vast libraries.
Correct answer is: It allows rapid screening of large peptide libraries for binding to a target
Q.86 Which of the following best describes the purpose of “adapter ligation” in library preparation for NGS?
To fluorescently label DNA fragments
To add known sequences required for amplification and sequencing to the fragment ends
To cut DNA into smaller pieces
To remove contaminating RNA
Explanation - Adapters contain primer binding sites and indices, allowing fragments to be amplified and identified during sequencing.
Correct answer is: To add known sequences required for amplification and sequencing to the fragment ends
Q.87 In the context of gene editing, a “PAM” sequence is:
A DNA motif required for Cas9 binding and cleavage
A protein domain of polymerase
A promoter element in eukaryotes
A type of RNA molecule
Explanation - Protospacer adjacent motif (PAM) is a short DNA sequence (e.g., NGG for SpCas9) adjacent to the target site, essential for Cas9 activity.
Correct answer is: A DNA motif required for Cas9 binding and cleavage
Q.88 Which of the following is a common method for introducing site‑directed mutations into a plasmid?
Random mutagenesis by UV exposure
PCR‑based mutagenesis using primers containing the desired change
Electroporation of the plasmid into cells
Restriction digestion without ligation
Explanation - Site‑directed mutagenesis uses primers with the intended mutation; the PCR product incorporates the change, which is then circularized.
Correct answer is: PCR‑based mutagenesis using primers containing the desired change
Q.89 The term “genome‑wide association study (GWAS)” refers to:
Sequencing an organism’s entire genome
Testing the association between genetic variants across the genome and a trait or disease
Measuring gene expression levels in all tissues
Cloning every gene in a genome
Explanation - GWAS scans many individuals for SNPs and correlates allele frequencies with phenotypic traits.
Correct answer is: Testing the association between genetic variants across the genome and a trait or disease
Q.90 Which of the following best explains why “high‑throughput screening (HTS)” is valuable in drug discovery?
It allows testing of millions of compounds quickly for activity against a target
It replaces animal testing completely
It sequences the genome of every pathogen
It synthesizes new DNA molecules automatically
Explanation - HTS uses automation and miniaturization to evaluate large chemical libraries for potential therapeutics.
Correct answer is: It allows testing of millions of compounds quickly for activity against a target
Q.91 In a bacterial two‑component regulatory system, the sensor kinase typically:
Binds DNA directly
Phosphorylates a response regulator upon sensing an environmental stimulus
Degrades mRNA
Acts as a ribosome
Explanation - The sensor kinase autophosphorylates and transfers the phosphate to a response regulator, which often alters gene expression.
Correct answer is: Phosphorylates a response regulator upon sensing an environmental stimulus
Q.92 Which of the following best describes the role of “splicing” in eukaryotic gene expression?
Removal of introns from pre‑mRNA to produce mature mRNA
Adding a poly‑A tail to the 3' end
Capping the 5' end of mRNA
Synthesizing tRNA
Explanation - Splicing removes non‑coding introns from the primary transcript, joining exons together to form functional mRNA.
Correct answer is: Removal of introns from pre‑mRNA to produce mature mRNA
Q.93 Which of the following enzymes is used to generate single‑stranded DNA (ssDNA) from double‑stranded plasmid DNA for certain cloning methods?
Exonuclease III
Exonuclease I
Lambda exonuclease
T5 exonuclease
Explanation - Lambda exonuclease degrades the 5'‑phosphorylated strand of dsDNA, leaving a 3'‑overhang ssDNA useful for cloning.
Correct answer is: Lambda exonuclease
Q.94 What does the acronym “RFLP” stand for, and what does it analyze?
Rapid Fragment Length Polymorphism; measures protein size
Restriction Fragment Length Polymorphism; detects variation in DNA fragment sizes after restriction digestion
RNA Fluorescence Localization Probe; visualizes RNA
Recombinant Fusion Linker Protein; tags proteins
Explanation - RFLP compares the pattern of DNA fragments produced by restriction enzymes, revealing genetic variation.
Correct answer is: Restriction Fragment Length Polymorphism; detects variation in DNA fragment sizes after restriction digestion
Q.95 In the context of synthetic biology, a “genetic toggle switch” is:
A device that can flip a gene on or off in response to an external stimulus
A method for measuring DNA melting temperature
A type of restriction enzyme
A technique for sequencing DNA
Explanation - A toggle switch uses mutually repressive regulatory elements to create a bistable system that can be switched between two states.
Correct answer is: A device that can flip a gene on or off in response to an external stimulus
Q.96 Which of the following best describes a “chromatin immunoprecipitation (ChIP)” assay?
It isolates DNA based on size through gel electrophoresis
It uses antibodies to pull down DNA‑protein complexes to identify binding sites of specific proteins
It measures RNA expression levels
It sequences whole genomes directly
Explanation - ChIP captures DNA fragments bound by a protein of interest, which are then identified by PCR or sequencing.
Correct answer is: It uses antibodies to pull down DNA‑protein complexes to identify binding sites of specific proteins
Q.97 Which of the following is a key feature of “long‑read sequencing platforms (e.g., PacBio, Oxford Nanopore)”?
They produce reads typically >10 kb, facilitating assembly of repetitive regions
They have the lowest error rates among all sequencing technologies
They require radioactive labeling
They can only sequence RNA
Explanation - Long‑read technologies generate continuous reads spanning large genomic regions, aiding in resolving complex repeats.
Correct answer is: They produce reads typically >10 kb, facilitating assembly of repetitive regions
Q.98 In the context of DNA‑based data storage, which of the following statements is TRUE?
DNA cannot store information longer than 100 base pairs
DNA offers extremely high data density and long‑term stability
Data can be retrieved from DNA without sequencing
DNA storage is currently faster than electronic hard drives
Explanation - DNA can theoretically store exabytes per gram and remain stable for thousands of years under proper conditions.
Correct answer is: DNA offers extremely high data density and long‑term stability
Q.99 Which of the following best defines the term “synthetic lethality” in the context of CRISPR screening?
Targeting a gene that is essential for all cells
Simultaneous disruption of two genes where loss of either alone is tolerated but loss of both is lethal
Introducing a lethal mutation into the genome
Using CRISPR to kill bacteria
Explanation - Synthetic lethal interactions reveal combinatorial dependencies that can be exploited for targeted therapies.
Correct answer is: Simultaneous disruption of two genes where loss of either alone is tolerated but loss of both is lethal