Which compound is used to stain DNA fragments for visualization in gel electrophoresis?

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

• Bromophenol blue
• Ethidium bromide
• Crystal violet
• Coomassie blue
Correct Option: B  [ Ethidium bromide ]

Remark: DNA fragments can be visualised only after staining the DNA with a compound known as ethidium bromide.

Ethidium bromide stained DNA bands appear bright orange when exposed to:

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

• Visible light
• Infrared radiation
• UV radiation
• Gamma rays
Correct Option: C  [ UV radiation ]

Remark: Bright orange coloured bands are seen when the stained gel is exposed to UV light.

The step of cutting out the separated bands of DNA from the agarose gel and extracting the DNA fragments is known as:

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

• Ligation
• Elution
• Spooling
• Denaturation
Correct Option: B  [ Elution ]

Remark: This step of extracting purified DNA fragments from the gel piece is known as elution.

Plasmids and bacteriophages used as cloning vectors replicate within bacterial cells:

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

• Dependent on chromosomal control
• Independent of chromosomal control
• Only during cell division
• Under the control of lysosomal enzymes
Correct Option: B  [ Independent of chromosomal control ]

Remark: Plasmids and bacteriophages have the ability to replicate within bacterial cells independent of the control of chromosomal DNA.

Which feature of bacteriophages makes them suitable vectors for achieving very high copy numbers of a linked alien DNA?

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

• Their small size
• Their high number per cell
• Their sticky ends
• Their resistance to antibiotics
Correct Option: B  [ Their high number per cell ]

Remark: Bacteriophages, because of their high number per cell, have very high copy numbers of their genome.

The vector sequence responsible for initiating replication and controlling the copy number of the linked DNA is the:

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

• Selectable marker
• Cloning site
• Origin of replication (ori)
• rop gene
Correct Option: C  [ Origin of replication (ori) ]

Remark: The ori sequence is responsible for initiating replication and controlling the copy number of the linked DNA.

A selectable marker in a vector serves the function of identifying and eliminating:

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

• Recombinants
• Non-transformants
• Competent cells
• Desired genes
Correct Option: B  [ Non-transformants ]

Remark: A selectable marker helps in identifying and eliminating non-transformants and selectively permitting the growth of the transformants.

Transformation is the procedure through which:

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

• DNA is cut into fragments
• DNA is joined with a vector
• A piece of DNA is introduced into a host bacterium
• DNA is extracted from the gel
Correct Option: C  [ A piece of DNA is introduced into a host bacterium ]

Remark: Transformation is a procedure through which a piece of DNA is introduced in a host bacterium.

Besides ampicillin, chloramphenicol, and tetracycline, which antibiotic resistance gene is listed as a useful selectable marker for *E. coli*?

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

• Penicillin
• Streptomycin
• Kanamycin
• Cycloserine
Correct Option: C  [ Kanamycin ]

Remark: Genes encoding resistance to antibiotics such as ampicillin, chloramphenicol, tetracycline or kanamycin, are useful selectable markers for E. coli.

Ideally, a cloning vector needs to have very few, preferably single, recognition sites for commonly used restriction enzymes because:

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

• Multiple sites increase vector stability
• Multiple sites complicate gene cloning
• Single sites prevent DNA ligase action
• Single sites reduce replication efficiency
Correct Option: B  [ Multiple sites complicate gene cloning ]

Remark: Presence of more than one recognition site within the vector will generate several fragments, which will complicate the gene cloning.