Part 3: Cloning Vectors (25 MCQs)
Part 3: Cloning Vectors – Plasmids, Bacteriophages, Features of Vectors (25 MCQs)
Q51. A cloning vector is:
a) DNA fragment to be cloned
b) DNA molecule used to carry foreign DNA into a host cell
c) Protein carrier
d) A bacterial enzyme
Answer: b
- b) Correct: Vectors = carriers of foreign DNA into host organisms.
Q52. Most commonly used vectors in genetic engineering are:
a) Plasmids and bacteriophages
b) Mitochondria
c) Ribosomes
d) Chromosomes
Answer: a
- a) Correct: Plasmids & bacteriophages are widely used cloning vectors.
Q53. A plasmid is best described as:
a) Linear RNA molecule
b) Small circular extrachromosomal DNA in bacteria
c) Viral protein coat
d) A bacterial chromosome
Answer: b
- b) Correct: Plasmids = small circular DNA, self-replicating.
Q54. Which plasmid was the first widely used cloning vector?
a) pUC18
b) pBR322
c) Ti plasmid
d) Cosmid
Answer: b
- b) Correct: pBR322 (E. coli plasmid) was the first artificial cloning vector.
Q55. Features required in a cloning vector include:
a) Origin of replication
b) Selectable marker genes
c) Restriction sites
d) All of the above
Answer: d
- d) Correct: Vectors need ORI + selectable markers + cloning sites.
Q56. ORI (origin of replication) is essential because it:
a) Selects transformed cells
b) Initiates replication of plasmid
c) Cuts DNA
d) Joins DNA fragments
Answer: b
- b) Correct: ORI = initiation site for DNA replication.
Q57. Selectable markers in vectors are used for:
a) Easy replication
b) Identifying transformed host cells
c) Ligating DNA
d) Sequencing DNA
Answer: b
- b) Correct: Markers (antibiotic resistance genes) help select recombinants.
Q58. Which selectable markers are present in pBR322?
a) Ampicillin & Tetracycline resistance genes
b) Kanamycin & Streptomycin resistance genes
c) Chloramphenicol only
d) None
Answer: a
- a) Correct: pBR322 has amp^R & tet^R genes.
Q59. Multiple Cloning Site (MCS) is also called:
a) Selectable marker
b) Polylinker region
c) ORI site
d) Replication terminator
Answer: b
- b) Correct: MCS = polylinker region with many RE sites.
Q60. Insertional inactivation refers to:
a) Antibiotic killing bacteria
b) Loss of marker gene activity due to insertion of foreign DNA
c) Cutting of plasmid DNA
d) Loss of ORI function
Answer: b
- b) Correct: Inserted DNA disrupts marker gene activity → selection possible.
Q61. Blue-white screening in pUC18 vector is based on:
a) Loss of tetracycline resistance
b) Inactivation of lacZ gene coding β-galactosidase
c) Resistance to ampicillin
d) Activation of GFP gene
Answer: b
- b) Correct: Recombinants = white colonies (lacZ disrupted), Non-recombinants = blue.
Q62. The lacZ gene product used in blue-white screening is:
a) Lactose permease
b) β-galactosidase
c) DNA ligase
d) Reverse transcriptase
Answer: b
- b) Correct: β-galactosidase cleaves X-gal → blue colonies.
Q63. Which of the following is a Ti plasmid?
a) Plasmid of Agrobacterium tumefaciens
b) Plasmid of Rhizobium
c) Plasmid of Bacillus
d) Plasmid of E. coli
Answer: a
- a) Correct: Ti plasmid (Agrobacterium) is used to transfer genes in plants.
Q64. Cosmid vectors are:
a) Combination of plasmid + phage λ cos sites
b) Linear mitochondrial DNA
c) Viral proteins
d) RNA fragments
Answer: a
- a) Correct: Cosmids = plasmid + λ cos site → high-capacity vectors.
Q65. Which cloning vector can carry the largest DNA fragment?
a) Plasmid
b) Cosmid
c) Bacteriophage
d) YAC (Yeast Artificial Chromosome)
Answer: d
- d) Correct: YACs can carry very large DNA inserts.
Q66. Which bacteriophage is commonly used as vector?
a) λ phage
b) T4 phage
c) ΦX174 phage
d) M13 phage
Answer: a
- a) Correct: λ bacteriophage widely used in genetic engineering.
Q67. Shuttle vectors are those which:
a) Can replicate in multiple host species
b) Can replicate in only one host
c) Lack selectable markers
d) Cannot carry foreign DNA
Answer: a
- a) Correct: Shuttle vectors replicate in more than one host (bacteria + yeast).
Q68. Which property is most essential for a plasmid vector?
a) Antibiotic resistance gene
b) ORI (origin of replication)
c) Restriction site
d) All of the above
Answer: d
- d) Correct: All features make plasmids suitable as vectors.
Q69. The cloning site in pBR322 is located in:
a) ORI region
b) Antibiotic resistance genes
c) Promoter region
d) RNA polymerase binding site
Answer: b
- b) Correct: Cloning sites are within amp^R or tet^R genes.
Q70. In blue-white screening, white colonies represent:
a) No foreign DNA present
b) Recombinant plasmid with disrupted lacZ gene
c) Bacteria killed by antibiotic
d) Virus-infected bacteria
Answer: b
- b) Correct: White = recombinants (lacZ inactivated).
Q71. Which of the following is a bacteriophage-based vector?
a) pUC19
b) λ phage vector
c) pBR322
d) Ti plasmid
Answer: b
- b) Correct: λ phage vectors widely used.
Q72. Which statement is INCORRECT for Ti plasmid?
a) Occurs in Agrobacterium tumefaciens
b) Causes crown gall disease
c) Used in animal gene transfer
d) Used for plant genetic engineering
Answer: c
- c) Correct: Ti plasmid = plant transformation vector, not animals.
Q73. Which is NOT a feature of a good cloning vector?
a) ORI
b) Selectable markers
c) Large size without replication ability
d) Multiple cloning sites
Answer: c
- c) Correct: Vectors must be small + replicating, not large & unstable.
Q74. Plasmids replicate:
a) Independently of bacterial chromosome
b) Only with bacterial DNA
c) Only during conjugation
d) Only when induced
Answer: a
- a) Correct: Plasmids = autonomous replication units.
Q75. Why are bacteriophages efficient cloning vectors?
a) High infection efficiency
b) Can carry larger DNA fragments than plasmids
c) Easy to manipulate
d) All of the above
Answer: d
- d) Correct: Phages infect efficiently, carry larger DNA, and are easily engineered.
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