If foreign DNA is ligated at the BamH I site in the vector pBR322, the BamH I site is located in the gene for resistance to:

[Biotechnology-Principles-and-Processes] [class-xii ]

• Ampicillin
• Chloramphenicol
• Tetracycline
• Kanamycin
Correct Option: C  [ Tetracycline ]

Remark: Foreign DNA can be ligated at the BamH I site of tetracycline resistance gene (*tetR*) in the vector pBR322.

Insertion of foreign DNA into the tetracycline resistance gene (*tetR*) of pBR322 causes the recombinant plasmids to lose tetracycline resistance. This phenomenon is called:

[Biotechnology-Principles-and-Processes] [class-xii ]

• Mutation of ori
• Loss of *rop* gene
• Insertional inactivation
• Non-transformation
Correct Option: C  [ Insertional inactivation ]

Remark: The recombinant plasmids will lose tetracycline resistance due to insertion of foreign DNA, which is referred to as insertional inactivation.

Why is the selection of recombinants using antibiotic resistance genes considered a cumbersome procedure?

[Biotechnology-Principles-and-Processes] [class-xii ]

• It requires high levels of expensive enzymes
• It requires simultaneous plating on two plates having different antibiotics
• It only works for prokaryotic hosts
• It leads to high levels of mutation
Correct Option: B  [ It requires simultaneous plating on two plates having different antibiotics ]

Remark: Selection of recombinants due to inactivation of antibiotics is cumbersome because it requires simultaneous plating on two plates.

Alternative selectable markers differentiate recombinants from non-recombinants primarily based on their ability to produce:

[Biotechnology-Principles-and-Processes] [class-xii ]

• Heat
• Light
• Colour
• Antibiotics
Correct Option: C  [ Colour ]

Remark: Alternative selectable markers differentiate recombinants on the basis of their ability to produce colour in the presence of a chromogenic substrate.

In chromogenic selection, the recombinant DNA is inserted within the coding sequence of which enzyme's gene?

[Biotechnology-Principles-and-Processes] [class-xii ]

• DNA ligase
• RNA polymerase
• β-galactosidase
• Protease
Correct Option: C  [ β-galactosidase ]

Remark: A recombinant DNA is inserted within the coding sequence of the enzyme $\beta$-galactosidase.

If a plasmid does not have an insert (non-recombinant) during chromogenic selection, the colonies appear:

[Biotechnology-Principles-and-Processes] [class-xii ]

• White
• Blue coloured
• Orange
• Red
Correct Option: B  [ Blue coloured ]

Remark: The presence of a chromogenic substrate gives blue coloured colonies if the plasmid in the bacteria does not have an insert.

Recombinant colonies in chromogenic selection are identified because they do not produce any colour, often appearing colourless or white, due to:

[Biotechnology-Principles-and-Processes] [class-xii ]

• Non-transformation
• Insertional inactivation of the β-galactosidase gene
• Inactivation of the *ori* gene
• Overexpression of the enzyme
Correct Option: B  [ Insertional inactivation of the β-galactosidase gene ]

Remark: Recombinant colonies do not produce any colour due to insertional inactivation of the $\beta$-galactosidase gene.

Which bacterium, a pathogen of several dicot plants, is used as a source for plant gene transfer vectors?

[Biotechnology-Principles-and-Processes] [class-xii ]

• Escherichia coli
• Salmonella typhimurium
• Agrobacterium tumifaciens
• Thermus aquaticus
Correct Option: C  [ Agrobacterium tumifaciens ]

Remark: *Agrobacterium tumifaciens* is a pathogen of several dicot plants used for transferring genes.

*Agrobacterium tumifaciens* delivers a piece of DNA known as ‘T-DNA’ to plant cells, resulting in the formation of a:

[Biotechnology-Principles-and-Processes] [class-xii ]

• Competent cell
• Tumor
• Plasmid
• Phage
Correct Option: B  [ Tumor ]

Remark: It delivers a piece of DNA known as ‘T-DNA’ to transform normal plant cells into a tumor.

In animals, which viral structures have the ability to transform normal cells into cancerous cells and have been disarmed for use as gene delivery vectors?

[Biotechnology-Principles-and-Processes] [class-xii ]

• Plasmids
• Bacteriophages
• Retroviruses
• Ti plasmids
Correct Option: C  [ Retroviruses ]

Remark: Retroviruses in animals have the ability to transform normal cells into cancerous cells, and have been disarmed for use as vectors.