Q.1 What is the primary purpose of a plasmid in bacterial transformation?
To serve as a source of nutrients for the cell
To replicate independently and carry foreign genes
To degrade unwanted DNA
To act as a ribosome
Explanation - Plasmids are circular DNA molecules that can replicate without chromosomal DNA and are used to introduce new genes into bacteria.
Correct answer is: To replicate independently and carry foreign genes
Q.2 Which enzyme is essential for cutting DNA at specific sequences during the creation of recombinant DNA?
DNA polymerase
RNA polymerase
Restriction endonuclease
Ligase
Explanation - Restriction endonucleases recognize specific DNA sequences and cleave the phosphodiester bond, allowing precise DNA fragment excision.
Correct answer is: Restriction endonuclease
Q.3 In the calcium chloride method of bacterial transformation, calcium ions primarily:
Destroy the bacterial cell wall
Facilitate DNA uptake by neutralizing charge
Break down plasmid DNA
Increase the temperature of the medium
Explanation - Ca²⁺ ions neutralize the negative charges on DNA and the bacterial membrane, making DNA entry easier during the heat‑shock step.
Correct answer is: Facilitate DNA uptake by neutralizing charge
Q.4 What is the role of DNA ligase in the construction of a recombinant plasmid?
To cut DNA at specific sites
To join DNA fragments together
To unwind the DNA helix
To synthesize RNA from a DNA template
Explanation - DNA ligase forms phosphodiester bonds between adjacent nucleotides, sealing nicks and joining fragments into a continuous strand.
Correct answer is: To join DNA fragments together
Q.5 Which of the following is a common selectable marker used in bacterial transformation?
Green fluorescent protein (GFP)
Ampicillin resistance gene (bla)
Beta‑galactosidase (lacZ)
Luciferase
Explanation - The bla gene confers resistance to ampicillin, allowing only transformed cells to grow on media containing the antibiotic.
Correct answer is: Ampicillin resistance gene (bla)
Q.6 Electroporation improves transformation efficiency by:
Heating the cells to high temperature
Applying a strong electric field to create temporary pores
Increasing the pH of the medium
Adding detergent to the culture
Explanation - The electric pulse induces transient pores in the cell membrane, allowing DNA to enter the cytoplasm more readily.
Correct answer is: Applying a strong electric field to create temporary pores
Q.7 What is a key difference between transformation and transfection?
Transformation occurs in prokaryotes, transfection in eukaryotes
Transformation uses viruses, transfection uses plasmids
Transformation is only for RNA, transfection only for DNA
There is no difference; they are synonymous
Explanation - Transformation traditionally refers to DNA uptake by bacteria, while transfection is the introduction of nucleic acids into eukaryotic cells.
Correct answer is: Transformation occurs in prokaryotes, transfection in eukaryotes
Q.8 Which of the following chemical methods is commonly used for mammalian cell transfection?
Calcium carbonate precipitation
Polyethylenimine (PEI)
Heat shock
Electroporation
Explanation - PEI forms positively charged complexes with DNA, facilitating its uptake by eukaryotic cells.
Correct answer is: Polyethylenimine (PEI)
Q.9 In the context of gene delivery, a ‘viral vector’ is primarily used because:
Viruses can replicate autonomously in any cell
They have high transfection efficiency and can enter many cell types
They are cheap to produce
They do not trigger immune responses
Explanation - Viruses have evolved mechanisms to deliver genetic material efficiently into host cells, making them effective vectors despite safety concerns.
Correct answer is: They have high transfection efficiency and can enter many cell types
Q.10 What is the purpose of a promoter sequence in a transfected plasmid?
To terminate transcription
To bind ribosomes for translation
To initiate transcription of the downstream gene
To degrade mRNA
Explanation - Promoters are DNA elements that recruit RNA polymerase and transcription factors to start gene expression.
Correct answer is: To initiate transcription of the downstream gene
Q.11 Which of the following best describes ‘stable transfection’?
Transient expression lasting a few days
Integration of foreign DNA into the host genome
DNA uptake without any selection pressure
Expression of RNA only
Explanation - Stable transfection results in the permanent incorporation of the transgene, allowing long‑term expression and inheritance by daughter cells.
Correct answer is: Integration of foreign DNA into the host genome
Q.12 Which selection marker is commonly used for stable transfection of mammalian cells?
Kanamycin resistance
Neomycin (G418) resistance
Ampicillin resistance
Tetracycline resistance
Explanation - The neomycin resistance gene (neo) allows cells that have integrated the plasmid to survive in the presence of G418 antibiotic.
Correct answer is: Neomycin (G418) resistance
Q.13 What does the term ‘MOI’ stand for in viral transduction experiments?
Molecular Oxygen Index
Multiplicity of Infection
Mass of Isolate
Maximum Output Intensity
Explanation - MOI indicates the ratio of infectious viral particles to target cells, influencing transduction efficiency.
Correct answer is: Multiplicity of Infection
Q.14 A common reporter gene used to monitor successful transfection is:
β‑actin
Green fluorescent protein (GFP)
LacI repressor
T7 RNA polymerase
Explanation - GFP emits fluorescence when expressed, allowing easy visual confirmation of gene delivery.
Correct answer is: Green fluorescent protein (GFP)
Q.15 During a heat‑shock transformation, the temperature jump to 42 °C primarily serves to:
Kill non‑transformed cells
Denature plasmid DNA
Create a thermal imbalance that facilitates DNA entry
Activate restriction enzymes
Explanation - The sudden temperature increase induces a temporary fluid phase in the membrane, allowing DNA to pass through.
Correct answer is: Create a thermal imbalance that facilitates DNA entry
Q.16 Which of the following is NOT a method for delivering DNA into plant cells?
Agrobacterium‑mediated transformation
Gene gun (biolistic) delivery
Electroporation of protoplasts
Lipid‑based transfection
Explanation - Lipid reagents are efficient for animal cells but are not typically used for plant cell walls; plant methods rely on Agrobacterium, biolistics, or protoplast electroporation.
Correct answer is: Lipid‑based transfection
Q.17 The ‘origin of replication’ (ori) in a plasmid is required for:
Transcription of the inserted gene
Replication of the plasmid inside the host cell
Integration into the host chromosome
Selection of transformed cells
Explanation - The ori is a DNA sequence recognized by host replication machinery, allowing the plasmid to be duplicated each cell cycle.
Correct answer is: Replication of the plasmid inside the host cell
Q.18 Which of the following best describes the term ‘competent cells’?
Cells that are actively dividing
Cells that have been genetically edited
Cells that can uptake foreign DNA efficiently
Cells that are resistant to antibiotics
Explanation - Competent cells have been treated to become permeable to DNA, enhancing transformation efficiency.
Correct answer is: Cells that can uptake foreign DNA efficiently
Q.19 In a typical bacterial transformation experiment, why is the antibiotic‑containing plate incubated overnight at 37 °C?
To inactivate the plasmid DNA
To promote growth of transformed colonies while inhibiting non‑transformed cells
To denature the antibiotic
To cause plasmid loss
Explanation - Only cells that have taken up the antibiotic‑resistance plasmid survive and form colonies under selective conditions.
Correct answer is: To promote growth of transformed colonies while inhibiting non‑transformed cells
Q.20 Which of the following statements about the CRISPR‑Cas9 system in the context of genetic transformation is true?
Cas9 integrates the donor DNA randomly
CRISPR requires a guide RNA to target a specific DNA sequence
CRISPR can only be used in bacterial cells
Cas9 cuts only RNA molecules
Explanation - The guide RNA directs Cas9 to a complementary DNA region where it creates a double‑strand break, enabling precise genome editing.
Correct answer is: CRISPR requires a guide RNA to target a specific DNA sequence
Q.21 What is the main advantage of using a ‘baculovirus’ vector for insect cell transfection?
It replicates in bacterial hosts
It can carry large DNA inserts up to 100 kb
It integrates into the host genome permanently
It does not require any selection markers
Explanation - Baculovirus vectors have high capacity for large foreign genes, making them suitable for expressing complex proteins in insect cells.
Correct answer is: It can carry large DNA inserts up to 100 kb
Q.22 In the context of gene therapy, which delivery method is considered non‑viral?
Adenovirus vector
Lentiviral vector
Nanoparticle‑mediated delivery
Retroviral vector
Explanation - Nanoparticles (lipid, polymer, or inorganic) can encapsulate DNA/RNA without using viral components, reducing immunogenicity.
Correct answer is: Nanoparticle‑mediated delivery
Q.23 A ‘shuttle vector’ is designed to:
Move between the nucleus and mitochondria
Replicate in both bacterial and eukaryotic cells
Transport proteins across membranes
Carry only RNA molecules
Explanation - Shuttle vectors contain origins of replication and selectable markers for both prokaryotic and eukaryotic hosts, facilitating cloning and expression steps.
Correct answer is: Replicate in both bacterial and eukaryotic cells
Q.24 Which of the following is a major limitation of electroporation for transfecting primary neurons?
Low DNA uptake efficiency
High cell mortality due to sensitivity to electric pulses
Requirement of calcium chloride
Inability to deliver RNA
Explanation - Primary neurons are fragile; the electric field needed for DNA entry often causes significant cell death, limiting electroporation use.
Correct answer is: High cell mortality due to sensitivity to electric pulses
Q.25 In bacterial transformation, the ‘blue/white screening’ method relies on the activity of:
β‑galactosidase
Lac repressor
Ampicillin β‑lactamase
GFP
Explanation - Insertion of foreign DNA disrupts the lacZ gene; colonies with functional β‑galactosidase turn blue on X‑gal, while disrupted ones remain white.
Correct answer is: β‑galactosidase
Q.26 Which of the following best explains why a high-copy-number plasmid yields more protein expression than a low-copy-number plasmid?
It integrates into the genome more efficiently
It contains a stronger promoter
It exists in more copies per cell, providing more template for transcription
It is more resistant to antibiotics
Explanation - Higher plasmid copy number increases the amount of mRNA that can be produced, leading to greater protein synthesis.
Correct answer is: It exists in more copies per cell, providing more template for transcription
Q.27 Which of the following statements about Lipofectamine is true?
It forms pores in the bacterial cell wall
It is a cationic lipid reagent that complexes with DNA
It requires a heat‑shock step
It permanently integrates DNA into the host genome
Explanation - Lipofectamine creates positively charged lipoplexes with DNA, facilitating endocytosis into eukaryotic cells.
Correct answer is: It is a cationic lipid reagent that complexes with DNA
Q.28 During a transfection experiment, why is serum often omitted from the medium during DNA‑lipid complex formation?
Serum degrades DNA
Serum interferes with lipid‑DNA complex formation
Serum causes cell death
Serum provides antibiotics that inhibit transfection
Explanation - Serum proteins can bind to lipids, reducing complex stability and transfection efficiency; they are re‑added after uptake.
Correct answer is: Serum interferes with lipid‑DNA complex formation
Q.29 What does the term ‘transient expression’ refer to in the context of gene delivery?
Permanent integration of DNA into the genome
Short‑term gene expression that lasts a few days without integration
Expression only under selective pressure
Expression limited to bacterial cells
Explanation - Transient expression results from episomal plasmids that are not integrated and are gradually lost as cells divide.
Correct answer is: Short‑term gene expression that lasts a few days without integration
Q.30 Which of the following is a common method for verifying successful plasmid insertion after transformation?
Gram staining
PCR amplification of the insert region
Measuring optical density at 600 nm
Electron microscopy
Explanation - Colony PCR quickly checks for the presence and correct size of the inserted DNA fragment.
Correct answer is: PCR amplification of the insert region
Q.31 In the context of genetic transformation, the term ‘homologous recombination’ is used to describe:
Random integration of DNA
Integration of DNA at a specific site sharing sequence similarity
DNA replication
RNA transcription
Explanation - Homologous recombination uses sequence homology to precisely insert DNA at the target locus.
Correct answer is: Integration of DNA at a specific site sharing sequence similarity
Q.32 Which of the following is NOT a typical component of a transfection reagent formulation?
Cationic lipids
Buffer salts
Antibiotics
Helper peptides
Explanation - Antibiotics are used for selection after transfection, not as part of the reagent that forms DNA complexes.
Correct answer is: Antibiotics
Q.33 A researcher wishes to introduce a gene into a bacterial chromosome rather than a plasmid. Which technique is most appropriate?
Electroporation with a circular plasmid
Conjugation using a mobilizable plasmid
Homologous recombination using a suicide vector
Calcium chloride transformation
Explanation - Suicide vectors cannot replicate in the host, so only cells that recombine the DNA into the chromosome survive.
Correct answer is: Homologous recombination using a suicide vector
Q.34 What is the primary function of the ‘poly‑A tail’ added to eukaryotic mRNA during transfection experiments?
To enhance transcription initiation
To stabilize mRNA and aid translation
To target mRNA for degradation
To act as a promoter
Explanation - The poly‑A tail protects mRNA from exonucleases and assists ribosome binding for efficient translation.
Correct answer is: To stabilize mRNA and aid translation
Q.35 In gene editing, a ‘donor template’ is required for:
Creating double‑strand breaks
Providing a sequence for homology‑directed repair
Inhibiting Cas9 activity
Acting as a selectable marker
Explanation - After Cas9 cuts DNA, the cell can use a supplied donor template to precisely insert or replace a sequence via HDR.
Correct answer is: Providing a sequence for homology‑directed repair
Q.36 Which method is most suitable for introducing siRNA into cultured mammalian cells?
Electroporation
Calcium chloride transformation
Liposome‑mediated transfection
Heat‑shock
Explanation - Cationic liposomes efficiently deliver small RNA molecules like siRNA into the cytoplasm of mammalian cells.
Correct answer is: Liposome‑mediated transfection
Q.37 What is the purpose of a ‘negative control’ in a transfection experiment?
To verify that the transfection reagent works
To show the baseline response without DNA
To select for successfully transfected cells
To increase expression levels
Explanation - A negative control contains all reagents except the nucleic acid, confirming that observed effects are due to the introduced DNA/RNA.
Correct answer is: To show the baseline response without DNA
Q.38 Which of the following describes the ‘Tat’ (Twin‑arginine translocation) pathway used in bacterial transformation?
A method for exporting folded proteins across the membrane
A type of antibiotic resistance mechanism
A DNA replication system
A plasmid segregation system
Explanation - The Tat pathway transports fully folded proteins, often used for secreting heterologous proteins in engineered bacteria.
Correct answer is: A method for exporting folded proteins across the membrane
Q.39 In mammalian cell culture, why is a ‘serum‑free’ medium sometimes used during transfection?
Serum blocks viral infection
Serum contains nucleases that degrade DNA
Serum interferes with lipid‑DNA complex formation
Serum causes cell differentiation
Explanation - Serum proteins can bind lipids, reducing transfection efficiency; serum‑free conditions improve uptake, then serum is restored for cell health.
Correct answer is: Serum interferes with lipid‑DNA complex formation
Q.40 What does the ‘pUC’ prefix in a plasmid name generally indicate?
The plasmid is derived from a yeast vector
It contains a high‑copy‑number origin of replication
It is a viral vector
It carries a mammalian promoter
Explanation - pUC plasmids are derived from the pBR322 family and contain the pMB1 origin, which supports high copy numbers in E. coli.
Correct answer is: It contains a high‑copy‑number origin of replication
Q.41 Which of the following is a common method for quantifying plasmid DNA concentration after purification?
Spectrophotometry at 260 nm
Gel electrophoresis staining intensity only
Measuring colony size
PCR cycle threshold
Explanation - DNA absorbs UV light at 260 nm; the absorbance allows calculation of concentration using Beer‑Lambert law.
Correct answer is: Spectrophotometry at 260 nm
Q.42 In the context of gene delivery, the term ‘endocytosis’ refers to:
Passive diffusion across the plasma membrane
Active uptake of DNA‑lipid complexes into vesicles
Integration of DNA into the genome
Direct injection of DNA into the nucleus
Explanation - Cationic lipoplexes are internalized by clathrin‑mediated or caveolae‑dependent endocytosis, after which DNA can escape into the cytoplasm.
Correct answer is: Active uptake of DNA‑lipid complexes into vesicles
Q.43 What is the purpose of the ‘terminator’ sequence in a transgene construct?
To start transcription
To signal the end of transcription and polyadenylation
To provide antibiotic resistance
To facilitate plasmid replication
Explanation - Terminator sequences direct RNA polymerase to stop transcription and often include signals for poly‑A tail addition in eukaryotes.
Correct answer is: To signal the end of transcription and polyadenylation
Q.44 Which of the following best describes the purpose of a ‘reporter gene’ in a transfection experiment?
To provide antibiotic resistance
To encode a detectable product for monitoring expression
To integrate the plasmid into the genome
To increase plasmid copy number
Explanation - Reporter genes such as GFP or luciferase produce measurable signals, allowing researchers to assess transfection efficiency and expression levels.
Correct answer is: To encode a detectable product for monitoring expression
Q.45 Which of the following statements about ‘RNA‑mediated transfection (RNAi)’ is correct?
It permanently alters the genome
It silences gene expression by degrading target mRNA
It requires integration of DNA into the host genome
It works only in bacterial cells
Explanation - RNA interference (RNAi) utilizes small interfering RNAs (siRNAs) that guide the RISC complex to cleave complementary mRNA, reducing protein production.
Correct answer is: It silences gene expression by degrading target mRNA
Q.46 The term ‘MOI = 1’ in a viral transduction experiment means:
Each cell receives exactly one viral particle
All cells are infected with multiple particles
The virus is non‑infectious
One milliliter of virus is added per million cells
Explanation - An MOI of 1 indicates an average of one infectious unit per cell, though distribution follows a Poisson model.
Correct answer is: Each cell receives exactly one viral particle
Q.47 A researcher uses a plasmid containing the CMV promoter. Which cell type is this promoter most likely designed for?
Bacterial cells
Plant cells
Mammalian cells
Yeast cells
Explanation - The cytomegalovirus (CMV) immediate‑early promoter is a strong, constitutive promoter widely used in mammalian expression vectors.
Correct answer is: Mammalian cells
Q.48 In a transformation experiment, why is the use of ‘competent cells’ often preferred over non‑competent cells?
Competent cells are resistant to all antibiotics
They have higher natural transformation rates
They can be stored indefinitely
They produce more plasmid DNA
Explanation - Competent cells have been chemically or physically treated to increase membrane permeability, greatly enhancing DNA uptake.
Correct answer is: They have higher natural transformation rates
Q.49 Which of the following is a safety concern specifically associated with viral vectors in gene therapy?
Antibiotic resistance spread
Insertional mutagenesis
Plasmid instability
High temperature sensitivity
Explanation - Viral integration can disrupt host genes or regulatory elements, potentially leading to oncogenesis.
Correct answer is: Insertional mutagenesis
Q.50 What is the main reason for using a ‘silencing RNA (shRNA)’ expression cassette instead of siRNA for long‑term gene knockdown?
shRNA is more stable in the cytoplasm
shRNA can be expressed from a plasmid for continuous production
shRNA does not require Dicer processing
shRNA integrates into the genome automatically
Explanation - shRNA vectors allow the host cell to transcribe short hairpin RNAs, providing sustained knockdown compared with transient siRNA delivery.
Correct answer is: shRNA can be expressed from a plasmid for continuous production
Q.51 Which of the following best explains why ‘heat‑shock’ is not used in mammalian cell transfection?
Mammalian cells lack a cell wall
Heat‑shock damages mammalian membranes
Mammalian cells already have high permeability
Heat‑shock only works with viral vectors
Explanation - Mammalian cell membranes are more sensitive to temperature spikes; heat‑shock would cause extensive cell death.
Correct answer is: Heat‑shock damages mammalian membranes
Q.52 In the context of plant transformation, the ‘Ti plasmid’ from Agrobacterium tumefaciens is used because:
It carries a strong bacterial promoter
It can transfer a segment of DNA (T‑DNA) into plant genomes
It is resistant to all plant antibiotics
It replicates autonomously in plant mitochondria
Explanation - Agrobacterium’s Ti plasmid naturally integrates T‑DNA into plant cells, a property exploited for genetic engineering.
Correct answer is: It can transfer a segment of DNA (T‑DNA) into plant genomes
Q.53 Which technique would you use to verify that a gene has been stably integrated into the host genome after transfection?
Southern blot analysis
Western blot analysis
Flow cytometry
RT‑PCR of mRNA
Explanation - Southern blot detects specific DNA fragments and can distinguish between episomal and integrated copies.
Correct answer is: Southern blot analysis
Q.54 The term ‘poly‑lysine coated plates’ is used in cell culture to:
Promote bacterial growth
Enhance adhesion of anchorage‑dependent mammalian cells during transfection
Increase antibiotic resistance
Facilitate viral infection
Explanation - Poly‑lysine provides a positively charged surface that improves cell attachment, especially when cells are stressed during transfection.
Correct answer is: Enhance adhesion of anchorage‑dependent mammalian cells during transfection
Q.55 Which of the following best describes the purpose of a ‘5′ untranslated region (5′ UTR)’ in a transgene construct?
To code for a peptide
To regulate translation efficiency
To provide antibiotic resistance
To act as a transcription terminator
Explanation - The 5′ UTR can contain regulatory elements such as ribosome binding sites or internal ribosome entry sites (IRES) that affect translation initiation.
Correct answer is: To regulate translation efficiency
Q.56 When using a CRISPR‑Cas9 plasmid for gene knockout, why is a ‘single‑guide RNA (sgRNA)’ required?
It provides the nuclease activity
It directs Cas9 to the specific genomic locus
It integrates the plasmid into the genome
It acts as a selectable marker
Explanation - The sgRNA contains a 20‑nt sequence complementary to the target DNA, guiding Cas9 to induce a double‑strand break at that site.
Correct answer is: It directs Cas9 to the specific genomic locus
Q.57 What is the main advantage of using a ‘mini‑circle DNA’ vector over conventional plasmids for transfection?
They contain viral genes for higher expression
They lack bacterial backbone, reducing immunogenicity and increasing expression
They integrate into the host genome more efficiently
They are resistant to nucleases
Explanation - Mini‑circles consist only of the expression cassette, resulting in higher and longer expression with lower toxicity.
Correct answer is: They lack bacterial backbone, reducing immunogenicity and increasing expression
Q.58 Which of the following is a commonly used method to increase the size of DNA that can be delivered by liposome‑based transfection?
Adding calcium chloride
Using a higher voltage electroporation step
Formulating with cationic polymers (e.g., PEI) in addition to lipids
Heat‑shock at 42 °C
Explanation - Hybrid lipid‑polymer complexes can condense larger DNA fragments and improve cellular uptake.
Correct answer is: Formulating with cationic polymers (e.g., PEI) in addition to lipids
Q.59 In bacterial transformation, the use of ‘blue/white screening’ depends on the presence of which substrate in the agar?
X‑gal
Ampicillin
IPTG
Kanamycin
Explanation - X‑gal is a chromogenic substrate for β‑galactosidase; colonies expressing functional lacZ turn blue.
Correct answer is: X‑gal
Q.60 What is the primary function of ‘RNA polymerase II’ in eukaryotic transfection experiments?
Transcribe rRNA genes
Transcribe tRNA genes
Transcribe messenger RNA from DNA templates
Integrate DNA into the genome
Explanation - RNA polymerase II synthesizes mRNA from protein‑coding genes, making it essential for expressing transgenes.
Correct answer is: Transcribe messenger RNA from DNA templates
Q.61 A ‘gene gun’ is primarily used for:
Delivering DNA into bacterial cells
Introducing DNA into plant cells with thick cell walls
Transfecting mammalian cells in suspension
Performing electroporation in yeast
Explanation - The biolistic method propels DNA-coated particles (gold/tungsten) into plant tissues, bypassing the cell wall barrier.
Correct answer is: Introducing DNA into plant cells with thick cell walls
Q.62 Which of the following is an advantage of using a ‘self‑replicating RNA (replicon)’ vector over a DNA plasmid for protein expression?
It integrates into the host genome
It avoids the need for nuclear entry and can achieve high cytoplasmic expression
It provides antibiotic selection
It is resistant to RNase degradation
Explanation - Self‑replicating RNA replicons replicate in the cytoplasm, eliminating the nuclear transport barrier and often giving higher protein yields.
Correct answer is: It avoids the need for nuclear entry and can achieve high cytoplasmic expression
Q.63 Which of the following best explains why a ‘high‑fidelity DNA polymerase’ is preferred for amplifying inserts for cloning?
It works at lower temperatures
It reduces the chance of introducing mutations during PCR
It increases the speed of the reaction
It adds extra nucleotides at the ends
Explanation - High‑fidelity enzymes possess proofreading activity, ensuring accurate DNA replication for downstream functional studies.
Correct answer is: It reduces the chance of introducing mutations during PCR
Q.64 What does the term ‘epigenetic silencing’ refer to in the context of transgene expression?
Mutation of the transgene sequence
Methylation or histone modifications that reduce transcription
Integration of the transgene into a silent locus
Deletion of the promoter region
Explanation - Epigenetic changes can repress transgene activity without altering the DNA sequence, leading to loss of expression over time.
Correct answer is: Methylation or histone modifications that reduce transcription
Q.65 When performing a bacterial transformation, why is it important to plate the cells on *selective* agar rather than non‑selective agar?
Selective agar speeds up colony growth
Selective agar ensures that only cells that have taken up the plasmid will grow
Non‑selective agar kills untransformed cells
Selective agar contains nutrients that increase plasmid copy number
Explanation - Selection pressure (e.g., antibiotic) allows growth only of cells harboring the resistance gene carried on the plasmid.
Correct answer is: Selective agar ensures that only cells that have taken up the plasmid will grow
Q.66 Which of the following is a typical use of the ‘T7 promoter’ in a plasmid vector?
Driving high‑level transcription in mammalian cells
Driving transcription in bacteria that express T7 RNA polymerase
Providing a terminator sequence
Conferring antibiotic resistance
Explanation - The T7 promoter is recognized by T7 RNA polymerase, which is supplied by host strains such as BL21(DE3) for robust protein expression.
Correct answer is: Driving transcription in bacteria that express T7 RNA polymerase
Q.67 In a transfection experiment, a ‘mock transfection’ control typically includes:
All reagents except the DNA/RNA
Only the DNA without any transfection reagent
Only the transfection reagent without DNA/RNA
Neither reagents nor DNA/RNA
Explanation - Mock transfection assesses any effects caused by the transfection reagent itself, separating them from nucleic acid–specific outcomes.
Correct answer is: Only the transfection reagent without DNA/RNA
Q.68 Which of the following is a common method to increase the uptake of plasmid DNA in hard‑to‑transfect cell lines?
Increasing the temperature to 42 °C
Using a nucleofection device that delivers DNA directly into the nucleus
Adding extra calcium chloride to the medium
Reducing the DNA concentration
Explanation - Nucleofection combines electrical pulses with specific solutions to transport DNA across both the plasma and nuclear membranes, improving efficiency in difficult cells.
Correct answer is: Using a nucleofection device that delivers DNA directly into the nucleus
Q.69 In the context of bacterial transformation, the term ‘blue/white screening’ is used to distinguish:
Plasmid size differences
Presence versus absence of an insert in the multiple cloning site
Antibiotic resistance levels
Cell morphology changes
Explanation - Insertion of foreign DNA disrupts lacZ α‑fragment, resulting in white colonies, whereas empty vectors yield blue colonies on X‑gal.
Correct answer is: Presence versus absence of an insert in the multiple cloning site
Q.70 Which of the following best explains why a ‘poly‑A signal’ is placed downstream of a coding sequence in a mammalian expression vector?
It promotes DNA replication
It signals termination of transcription and addition of a poly‑A tail to mRNA
It encodes a fluorescent protein
It provides resistance to ampicillin
Explanation - The poly‑A signal directs cleavage of the nascent transcript and polyadenylation, enhancing mRNA stability and export.
Correct answer is: It signals termination of transcription and addition of a poly‑A tail to mRNA
Q.71 When using a viral vector for gene delivery, which of the following is a strategy to reduce the immune response in the host?
Using a higher MOI
Choosing a serotype with low pre‑existing immunity
Adding antibiotics to the culture
Heat‑inactivating the virus
Explanation - Selecting viral capsids that the host has not been exposed to reduces neutralizing antibody formation and improves transduction efficiency.
Correct answer is: Choosing a serotype with low pre‑existing immunity
Q.72 The ‘pUC19’ plasmid contains a multiple cloning site (MCS). What is the purpose of an MCS?
To provide antibiotic resistance
To allow insertion of foreign DNA at a defined location
To replicate the plasmid in eukaryotic cells
To encode a fluorescent marker
Explanation - An MCS is a short DNA segment with many unique restriction sites, facilitating easy cloning of inserts.
Correct answer is: To allow insertion of foreign DNA at a defined location
Q.73 In a transfection protocol, why is it recommended to replace the transfection medium after 4–6 hours?
To remove excess DNA that could be toxic
To add more transfection reagent
To supply fresh nutrients and reduce cytotoxicity from the reagent
To increase the temperature of the culture
Explanation - Many transfection reagents are toxic over prolonged exposure; changing the medium improves cell viability while allowing expression to continue.
Correct answer is: To supply fresh nutrients and reduce cytotoxicity from the reagent
Q.74 Which of the following best describes a ‘non‑integrating lentiviral vector’ (NILV)?
A vector that integrates into the host genome at random sites
A vector that delivers DNA that remains episomal, reducing insertional mutagenesis risk
A vector that cannot infect dividing cells
A vector that only carries RNA, not DNA
Explanation - NILVs are engineered to lack integrase activity, so the transgene persists as an episome, offering safer long‑term expression.
Correct answer is: A vector that delivers DNA that remains episomal, reducing insertional mutagenesis risk
Q.75 In a typical PCR‑based cloning workflow, why is a ‘high‑fidelity polymerase’ often used to amplify the gene of interest?
It adds a 5′ cap to the product
It reduces the chance of point mutations that could affect protein function
It shortens the reaction time
It produces blunt ends suitable for ligation
Explanation - High‑fidelity enzymes possess proofreading activity, which minimizes incorporation errors during amplification.
Correct answer is: It reduces the chance of point mutations that could affect protein function
Q.76 Which of the following statements about ‘RNA‑based vaccines’ (e.g., mRNA vaccines) is true?
They integrate into the host genome
They require a viral vector for delivery
They rely on host ribosomes to translate the delivered mRNA into antigen protein
They are only effective in bacterial cells
Explanation - mRNA vaccines deliver synthetic mRNA that is translated by the host’s translational machinery to produce antigenic proteins, eliciting an immune response.
Correct answer is: They rely on host ribosomes to translate the delivered mRNA into antigen protein
Q.77 The ‘CMV enhancer’ is often placed upstream of a promoter in mammalian vectors to:
Reduce transcriptional activity
Increase transcriptional strength and broad expression
Provide antibiotic resistance
Facilitate plasmid replication
Explanation - The CMV enhancer boosts promoter activity, leading to higher levels of transgene expression across many cell types.
Correct answer is: Increase transcriptional strength and broad expression
Q.78 In the context of genetic transformation, a ‘reporter assay’ is used to:
Select for antibiotic‑resistant cells
Quantify the efficiency of gene delivery by measuring a detectable output
Integrate DNA into the genome
Destroy unwanted plasmids
Explanation - Reporter assays (e.g., luciferase, GFP) provide a measurable signal proportional to transgene expression, allowing assessment of transfection efficiency.
Correct answer is: Quantify the efficiency of gene delivery by measuring a detectable output
Q.79 Which of the following is a potential disadvantage of using calcium phosphate precipitation for mammalian cell transfection?
It requires high temperatures
It can lead to variable efficiency and formation of cytotoxic precipitates
It integrates DNA into the host genome
It is only applicable to bacterial cells
Explanation - Calcium phosphate can form large aggregates that are toxic and cause inconsistent DNA delivery across experiments.
Correct answer is: It can lead to variable efficiency and formation of cytotoxic precipitates
Q.80 A ‘gene silencing’ approach that utilizes short hairpin RNA (shRNA) is typically delivered via:
A viral vector
Electroporation of plasmid DNA only
Direct injection of synthetic siRNA
Heat‑shock transformation
Explanation - Viral vectors (e.g., lentivirus) can stably integrate shRNA expression cassettes, enabling long‑term knockdown.
Correct answer is: A viral vector
Q.81 When cloning a gene into a plasmid, why is it important to maintain the correct reading frame at the junction of the insert and vector?
To ensure the plasmid replicates correctly
To guarantee proper transcription termination
To produce a functional protein without premature stop codons
To allow antibiotic resistance
Explanation - A shift in reading frame can alter codon interpretation, leading to truncated or non‑functional proteins.
Correct answer is: To produce a functional protein without premature stop codons
Q.82 Which of the following best describes the purpose of a ‘selection marker’ in a plasmid used for transformation?
To enhance transcription of the gene of interest
To provide a means of identifying cells that have taken up the plasmid
To increase plasmid copy number
To promote cell adhesion
Explanation - Selection markers (e.g., antibiotic resistance genes) allow growth of only transformed cells under selective conditions.
Correct answer is: To provide a means of identifying cells that have taken up the plasmid
Q.83 In a bacterial transformation protocol, which step is typically performed *after* the heat‑shock and *before* plating on selective media?
Incubation in SOC medium for recovery
Addition of CaCl₂ solution
Electroporation
DNA purification
Explanation - The recovery step allows cells to express the antibiotic resistance gene before being exposed to selection.
Correct answer is: Incubation in SOC medium for recovery
Q.84 Which of the following is a characteristic of a ‘high‑copy‑number plasmid’?
It integrates into the host chromosome
It typically yields 50–100 copies per cell
It requires a viral helper for replication
It cannot be used in Gram‑positive bacteria
Explanation - High‑copy plasmids replicate autonomously to produce many copies per bacterial cell, enhancing gene expression.
Correct answer is: It typically yields 50–100 copies per cell
Q.85 In gene therapy, the term ‘ex vivo transfection’ refers to:
Transfecting cells directly inside the patient
Transfecting cells outside the body and then re‑implanting them
Injecting viral vectors directly into tissues
Using electroporation on whole organisms
Explanation - Ex vivo approaches involve modifying cells in culture, then delivering them back to the patient, allowing better control and selection.
Correct answer is: Transfecting cells outside the body and then re‑implanting them
Q.86 Which of the following best explains why a ‘poly‑A tail’ is added to eukaryotic mRNA during transcription?
To signal termination of transcription
To protect the mRNA from exonucleases and aid nuclear export
To act as a ribosome binding site
To provide a site for DNA replication
Explanation - The poly‑A tail stabilizes mRNA and is recognized by proteins that transport it from the nucleus to the cytoplasm.
Correct answer is: To protect the mRNA from exonucleases and aid nuclear export
Q.87 During a transfection experiment, the presence of a strong fluorescent signal in only a small fraction of cells most likely indicates:
High transfection efficiency
Low transfection efficiency
Complete plasmid integration
Cell death
Explanation - If only few cells fluoresce, the delivery method is not efficiently introducing DNA into the majority of cells.
Correct answer is: Low transfection efficiency
Q.88 Which of the following is a common method for delivering DNA into *yeast* cells?
Calcium chloride transformation
Lithium acetate/PEG method
Lipofectamine
Agrobacterium infection
Explanation - The LiAc/PEG protocol makes yeast cell walls permeable to DNA, facilitating transformation.
Correct answer is: Lithium acetate/PEG method
Q.89 The term ‘homology arm’ in a gene‑targeting vector refers to:
A sequence that encodes the antibiotic resistance gene
Regions flanking the insert that are identical to the target genome for recombination
A promoter for driving expression
A sequence that induces RNA interference
Explanation - Homology arms guide precise insertion of the construct via homologous recombination at the desired locus.
Correct answer is: Regions flanking the insert that are identical to the target genome for recombination
Q.90 Which of the following is NOT a typical component of a bacterial expression vector?
Origin of replication
Antibiotic resistance gene
Eukaryotic poly‑A signal
Multiple cloning site
Explanation - A poly‑A signal is required for eukaryotic mRNA processing and is unnecessary in bacterial vectors.
Correct answer is: Eukaryotic poly‑A signal
Q.91 When performing a *stable* transfection in mammalian cells, why is *clonal selection* often performed after initial transfection?
To ensure all cells have the same copy number and integration site
To increase transient expression
To remove the selection marker
To speed up cell growth
Explanation - Clonal selection isolates individual cells with desirable integration events, providing a uniform population for experiments.
Correct answer is: To ensure all cells have the same copy number and integration site
Q.92 Which of the following best describes the purpose of a ‘ribosome binding site (RBS)’ in a bacterial expression construct?
To initiate transcription
To recruit ribosomes for translation initiation
To provide antibiotic resistance
To terminate transcription
Explanation - The RBS (e.g., Shine‑Dalgarno sequence) aligns the ribosome with the start codon, enabling translation of the mRNA.
Correct answer is: To recruit ribosomes for translation initiation
Q.93 In a CRISPR knock‑in experiment, which repair pathway is exploited to insert a donor DNA template at the target site?
Non‑homologous end joining (NHEJ)
Base excision repair (BER)
Homology‑directed repair (HDR)
Mismatch repair (MMR)
Explanation - HDR uses a homologous donor template to precisely insert new DNA at the double‑strand break created by Cas9.
Correct answer is: Homology‑directed repair (HDR)
Q.94 Which of the following is a key advantage of using *microinjection* for introducing DNA into embryos?
It can target many cells simultaneously
It does not require specialized equipment
It allows precise delivery of DNA into the pronucleus of a single cell
It works equally well in plant tissue
Explanation - Microinjection directly deposits DNA into the nucleus of a fertilized egg, enabling generation of transgenic organisms.
Correct answer is: It allows precise delivery of DNA into the pronucleus of a single cell
Q.95 In the context of *viral* transduction, the term ‘pseudotyping’ refers to:
Using a virus that cannot replicate
Replacing the native viral envelope protein with one from another virus to alter tropism
Integrating the viral genome into host DNA
Mutating the viral capsid to increase size
Explanation - Pseudotyping changes the viral surface proteins, enabling the virus to infect different cell types or improve stability.
Correct answer is: Replacing the native viral envelope protein with one from another virus to alter tropism
Q.96 What is the main function of the *poly‑histidine tag* (His‑tag) when added to a recombinant protein expressed after transformation?
To increase transcriptional activity
To facilitate purification using metal‑affinity chromatography
To provide antibiotic resistance
To enhance fluorescence
Explanation - His‑tags bind to nickel or cobalt ions on chromatography resins, allowing easy purification of the recombinant protein.
Correct answer is: To facilitate purification using metal‑affinity chromatography
Q.97 Which of the following is a typical *negative* control for a CRISPR‑Cas9 genome‑editing experiment?
A plasmid encoding Cas9 and a non‑targeting sgRNA
A plasmid with a strong promoter
A plasmid containing the donor template only
A plasmid with a fluorescent reporter
Explanation - A non‑targeting sgRNA controls for effects caused by Cas9 expression alone, without inducing cuts at specific genomic loci.
Correct answer is: A plasmid encoding Cas9 and a non‑targeting sgRNA
Q.98 During a *transient* transfection, why might the expression level of the introduced gene decline after several days?
The plasmid becomes integrated and silenced
The plasmid is diluted out as cells divide and is not replicated
The antibiotic degrades the plasmid
The promoter is turned off by the host
Explanation - Episomal plasmids are not maintained without selection, so their copy number decreases with cell division, reducing expression.
Correct answer is: The plasmid is diluted out as cells divide and is not replicated
Q.99 In a *gene‑silencing* experiment using RNAi, which molecule is directly responsible for cleaving the target mRNA?
Dicer
Argonaute (part of RISC)
RNA polymerase II
Reverse transcriptase
Explanation - The Argonaute protein within the RNA‑induced silencing complex (RISC) slices complementary mRNA, leading to its degradation.
Correct answer is: Argonaute (part of RISC)
Q.100 Which of the following best explains why *codon optimization* may be performed on a gene before cloning into a mammalian expression vector?
To increase the size of the gene
To replace rare codons with those preferred by the host, improving translation efficiency
To add a selectable marker
To create a fluorescent protein
Explanation - Optimizing codon usage aligns the gene with the host’s tRNA pool, enhancing protein production.
Correct answer is: To replace rare codons with those preferred by the host, improving translation efficiency
Q.101 In a *bacterial* transformation, which of the following conditions is NOT required for successful uptake of plasmid DNA?
Cold incubation on ice
Heat‑shock at 42 °C
Presence of a selectable marker
Addition of a viral envelope protein
Explanation - Viral envelope proteins are irrelevant for bacterial transformation; the process relies on chemical competence and heat‑shock.
Correct answer is: Addition of a viral envelope protein
Q.102 Which of the following is a reason to use a *low‑copy‑number* plasmid rather than a high‑copy one?
To increase the speed of bacterial growth
To reduce metabolic burden and toxicity of overexpressed proteins
To ensure integration into the host genome
To allow antibiotic resistance at lower concentrations
Explanation - High expression from a high‑copy plasmid can be toxic; low‑copy plasmids provide moderate expression and less stress on the host.
Correct answer is: To reduce metabolic burden and toxicity of overexpressed proteins
Q.103 In a *transient transfection* experiment, why is a *reporter plasmid* often co‑transfected with the experimental plasmid?
To increase antibiotic resistance
To normalize for transfection efficiency across samples
To integrate both plasmids into the genome
To degrade the experimental plasmid after expression
Explanation - The reporter provides a reference signal that accounts for variations in delivery, allowing accurate comparison of experimental effects.
Correct answer is: To normalize for transfection efficiency across samples
Q.104 Which of the following statements about *DNA nanostructures* used for gene delivery is TRUE?
They cannot be functionalized with targeting ligands
They are always more efficient than viral vectors
They can be engineered to protect DNA from nucleases and enable targeted delivery
They integrate into the host genome automatically
Explanation - DNA nanostructures can be designed with protective coatings and ligands for specific cell targeting, improving stability and delivery.
Correct answer is: They can be engineered to protect DNA from nucleases and enable targeted delivery
Q.105 When using *lipofection*, what role does the *cationic lipid* component play?
It degrades extracellular DNA
It forms positively charged complexes with negatively charged DNA, facilitating membrane interaction
It provides antibiotic resistance
It directly integrates DNA into the genome
Explanation - Cationic lipids neutralize DNA charge, allowing the complex to fuse with the negatively charged cell membrane.
Correct answer is: It forms positively charged complexes with negatively charged DNA, facilitating membrane interaction
Q.106 Which of the following is a characteristic feature of *non‑integrating lentiviral vectors* (NILVs)?
They permanently integrate into the host genome
They express transgenes episomally, reducing insertional mutagenesis risk
They cannot infect dividing cells
They require a bacterial host for replication
Explanation - NILVs lack functional integrase, so the transgene remains as an episome, offering safer long‑term expression.
Correct answer is: They express transgenes episomally, reducing insertional mutagenesis risk
Q.107 In the context of *plant* genetic transformation, the *gene gun* method uses which of the following to deliver DNA?
Calcium chloride solution
Gold or tungsten microparticles coated with DNA
Viral particles
Electroporation pulses
Explanation - The biolistic approach propels DNA‑coated metal particles into plant tissue, bypassing the cell wall barrier.
Correct answer is: Gold or tungsten microparticles coated with DNA