Cloning Vectors Questions and Answers

Q: Which one of the following vector types is suitable to clone 2000 kb DNA insert?

A 2000 kb insert needs a yeast artificial chromosome (YAC).2000 kb is 2 Mb. YACs carry a centromere, telomeres and an origin of replication, so they are maintained like natural yeast chromosomes and can hold inserts from about 100 kb up to the megabase range, which made them the vector of choice for early genome mapping.The other vectors are far too small: a bacterial plasmid carries up to roughly 10-15 kb, a lambda bacteriophage vector about 20-25 kb, and a cosmid about 35-45 kb, since it must still be packaged into a phage head.

Q: Two micron plasmid can be obtained from the following yeast :

The two micron plasmid is obtained from Saccharomyces cerevisiae.The 2-micron (2 µm) plasmid is a circular DNA of about 6.3 kb, named for its contour length, present in some 40-60 copies per cell in most strains of baker's yeast. Its origin of replication is used to build high-copy yeast episomal plasmid vectors (YEp).Candida shehatae, Pichia pastoris and the fission yeast Schizosaccharomyces pombe do not carry the 2-micron plasmid.

Q: Which of the following is a phagemid vector ?

The phagemid vector is pBluescript.A phagemid is a plasmid that also carries the origin of replication of a filamentous phage such as f1 or M13. pBluescript has the f1 origin, so in cells infected with a helper phage it can be packaged as single-stranded DNA, useful for sequencing and mutagenesis, while it otherwise replicates as an ordinary plasmid.pUC19 and pBR322 are plain plasmid vectors with no phage origin, and λEMBL3 is a lambda replacement vector, a phage rather than a phagemid.

Q: Root Inducing (RI) plasmid was derived from :

The Ri plasmid comes from Agrobacterium rhizogenes.A. rhizogenes causes hairy root disease. Its root-inducing (Ri) plasmid transfers T-DNA carrying the rol genes into plant cells, which then proliferate as masses of fast-growing roots; hairy root cultures are used to produce plant metabolites.A. tumefaciens carries the tumour-inducing (Ti) plasmid and causes crown gall. Azotobacter and Azospirillum are free-living and associative nitrogen-fixing bacteria with no such plasmid.

Q: Ti plasmid used in genetic engineering is obtained from :

The Ti plasmid is obtained from Agrobacterium tumifaciens (A. tumefaciens).The tumour-inducing (Ti) plasmid of this soil bacterium carries a segment, the T-DNA, that is transferred into the plant genome and causes crown gall. In engineered vectors the tumour genes are removed and the gene of interest is placed between the T-DNA borders, so the bacterium delivers it into plant cells.Agrobacterium rhizogenes carries the related Ri (root-inducing) plasmid that causes hairy root. Bacillus thuringiensis is the source of Bt toxin genes, and Thermus aquaticus the source of Taq polymerase.

Q: A vector is designed to replicate in both, E.coli and Streptomyces. It is reconstructed from E.coli plasmid and streptomyces plasmid. What is the type of such vectors ?

Such vectors are Shuttle vectors.A shuttle vector carries origins of replication (and selectable markers) for two different hosts, so it can be propagated in E. coli, where cloning is easy, and then moved into a second organism such as Streptomyces or yeast for expression or study. Joining an E. coli plasmid to a Streptomyces plasmid gives exactly this.A phagemid combines a plasmid with a phage origin so that single-stranded DNA can be packaged. BACs and YACs are vectors for very large inserts, based on the bacterial F plasmid and on yeast chromosome elements respectively; their defining feature is insert size, not replication in two hosts.

Q: Consider the following statements about binary vector used for plant transformation ?(i) Binary vector are Agrobacterium based vectors(ii) Binary vector contains both bacterial and plant selectable marker(iii) Binary vector have virulence (Vir) region(iv) There is presence of T-DNA left and right border repeat sequencesWhich of the above statements are correct :

Statements (i), (ii) and (iv) are correct.A binary vector system splits the Ti plasmid's functions between two plasmids in Agrobacterium (i). The small binary vector carries the T-DNA left and right border repeats (iv), with the gene of interest and a plant selectable marker between them, and a bacterial selectable marker and origins outside the borders for growth in E. coli and Agrobacterium (ii).Statement (iii) is false. The virulence (vir) genes are on the second, disarmed helper Ti plasmid, which acts in trans to transfer the T-DNA. That is the point of the binary design, so every option including (iii) is wrong.

Q: Which of the following is NOT correct for an ideal plasmid cloning vector ?

The feature that is not correct is the absence of an origin of replication.A plasmid vector must replicate in the host cell to be maintained and multiplied, so an origin of replication is essential. Without one the vector and its insert would be lost as the cells divide.The other features are desirable. A small size makes the plasmid easy to handle, gives a high copy number and leaves room for inserts. A multiple cloning site offers unique restriction sites for inserting DNA, and a selectable marker such as antibiotic resistance identifies cells that carry the vector.

Which one of the following vector types is suitable to clone 2000 kb DNA insert?

A.Bacterial plasmid
B.Bacteriophage
C.Cosmid
D.Yeast artificial chromosome

Exam Year(s)

IIT JAM - 2026,

Answer: D

A 2000 kb insert needs a yeast artificial chromosome (YAC).

2000 kb is 2 Mb. YACs carry a centromere, telomeres and an origin of replication, so they are maintained like natural yeast chromosomes and can hold inserts from about 100 kb up to the megabase range, which made them the vector of choice for early genome mapping.

The other vectors are far too small: a bacterial plasmid carries up to roughly 10-15 kb, a lambda bacteriophage vector about 20-25 kb, and a cosmid about 35-45 kb, since it must still be packaged into a phage head.

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Two micron plasmid can be obtained from the following yeast :

A.Candida shehatae
B.Pichia pastoris
C.Schizosaccharomyces pombe
D.Saccharomyces cerevisiae

Exam Year(s)

MH SET - 2019, SET Exam - 2019,

Answer: D

The two micron plasmid is obtained from Saccharomyces cerevisiae.

The 2-micron (2 µm) plasmid is a circular DNA of about 6.3 kb, named for its contour length, present in some 40-60 copies per cell in most strains of baker's yeast. Its origin of replication is used to build high-copy yeast episomal plasmid vectors (YEp).

Candida shehatae, Pichia pastoris and the fission yeast Schizosaccharomyces pombe do not carry the 2-micron plasmid.

Discuss in Forum

Which of the following is a phagemid vector ?

A.pUC19
B.pBR322
C.λEMBL3
D.p Bluescript

Exam Year(s)

MH SET - 2019, SET Exam - 2019,

Answer: D

The phagemid vector is pBluescript.

A phagemid is a plasmid that also carries the origin of replication of a filamentous phage such as f1 or M13. pBluescript has the f1 origin, so in cells infected with a helper phage it can be packaged as single-stranded DNA, useful for sequencing and mutagenesis, while it otherwise replicates as an ordinary plasmid.

pUC19 and pBR322 are plain plasmid vectors with no phage origin, and λEMBL3 is a lambda replacement vector, a phage rather than a phagemid.

Discuss in Forum

Root Inducing (RI) plasmid was derived from :

A.Agrobacterium tumefaciens
B.Agrobacterium rhizogenes
C.Azotobacter vinelandii
D.Azospirillum brasilense

Exam Year(s)

MH SET - 2020, SET Exam - 2020,

Answer: B

The Ri plasmid comes from Agrobacterium rhizogenes.

A. rhizogenes causes hairy root disease. Its root-inducing (Ri) plasmid transfers T-DNA carrying the rol genes into plant cells, which then proliferate as masses of fast-growing roots; hairy root cultures are used to produce plant metabolites.

A. tumefaciens carries the tumour-inducing (Ti) plasmid and causes crown gall. Azotobacter and Azospirillum are free-living and associative nitrogen-fixing bacteria with no such plasmid.

Discuss in Forum

Ti plasmid used in genetic engineering is obtained from :

A.Bacillus thuringensis
B.Agrobacterium shizogenes
C.Thermus aquaticus
D.Agrobacterium tumifaciens

Exam Year(s)

MH SET - 2021, SET Exam - 2021,

Answer: D

The Ti plasmid is obtained from Agrobacterium tumifaciens (A. tumefaciens).

The tumour-inducing (Ti) plasmid of this soil bacterium carries a segment, the T-DNA, that is transferred into the plant genome and causes crown gall. In engineered vectors the tumour genes are removed and the gene of interest is placed between the T-DNA borders, so the bacterium delivers it into plant cells.

Agrobacterium rhizogenes carries the related Ri (root-inducing) plasmid that causes hairy root. Bacillus thuringiensis is the source of Bt toxin genes, and Thermus aquaticus the source of Taq polymerase.

Discuss in Forum

A vector is designed to replicate in both, E.coli and Streptomyces. It is reconstructed from E.coli plasmid and streptomyces plasmid. What is the type of such vectors ?

A.Phagemid vectors
B.Shuttle vectors
C.BAC vectors
D.YAC vectors

Exam Year(s)

MH SET - 2023, SET Exam - 2023,

Answer: B

Such vectors are Shuttle vectors.

A shuttle vector carries origins of replication (and selectable markers) for two different hosts, so it can be propagated in E. coli, where cloning is easy, and then moved into a second organism such as Streptomyces or yeast for expression or study. Joining an E. coli plasmid to a Streptomyces plasmid gives exactly this.

A phagemid combines a plasmid with a phage origin so that single-stranded DNA can be packaged. BACs and YACs are vectors for very large inserts, based on the bacterial F plasmid and on yeast chromosome elements respectively; their defining feature is insert size, not replication in two hosts.

Discuss in Forum

Consider the following statements about binary vector used for plant transformation ?

(i) Binary vector are Agrobacterium based vectors
(ii) Binary vector contains both bacterial and plant selectable marker
(iii) Binary vector have virulence (Vir) region
(iv) There is presence of T-DNA left and right border repeat sequences

Which of the above statements are correct :

A.(i), (ii), (iii) and (iv)
B.(i), (ii) and (iii)
C.(i), (ii) and (iv)
D.(ii), (iii) and (iv)

Exam Year(s)

MH SET - 2025, SET Exam - 2025,

Answer: C

Statements (i), (ii) and (iv) are correct.

A binary vector system splits the Ti plasmid's functions between two plasmids in Agrobacterium (i). The small binary vector carries the T-DNA left and right border repeats (iv), with the gene of interest and a plant selectable marker between them, and a bacterial selectable marker and origins outside the borders for growth in E. coli and Agrobacterium (ii).

Statement (iii) is false. The virulence (vir) genes are on the second, disarmed helper Ti plasmid, which acts in trans to transfer the T-DNA. That is the point of the binary design, so every option including (iii) is wrong.

Discuss in Forum

Which of the following is NOT correct for an ideal plasmid cloning vector ?

A.Smaller size
B.Presence of multiple cloning site
C.Absence of origin of replication
D.Presence of selectable marker

Exam Year(s)

MH SET - 2025, SET Exam - 2025,

Answer: C

The feature that is not correct is the absence of an origin of replication.

A plasmid vector must replicate in the host cell to be maintained and multiplied, so an origin of replication is essential. Without one the vector and its insert would be lost as the cells divide.

The other features are desirable. A small size makes the plasmid easy to handle, gives a high copy number and leaves room for inserts. A multiple cloning site offers unique restriction sites for inserting DNA, and a selectable marker such as antibiotic resistance identifies cells that carry the vector.

Discuss in Forum

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