biology : class12 Selectable Markers : DNA Isolation, Restriction Enzymes, Vector, Ligation, Host Cell : Recombinant DNA Technology MCQ Questions and Answers
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Selectable Markers
MCQ questions and answers.
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MCQ Questions
1. What is the main function of a selectable marker in a cloning vector?
A.
To identify host cells that have taken up the vector
B.
To cut DNA at specific sites
C.
To join two DNA fragments
D.
To produce ribosomes in the host cell
Correct Answer:
To identify host cells that have taken up the vector
Explanation:
A selectable marker helps identify or select host cells that have received the recombinant vector, commonly through antibiotic resistance.
2. Which of the following is commonly used as a selectable marker in plasmid vectors?
A.
Antibiotic resistance gene
B.
Ribosomal RNA gene
C.
Cell wall gene
D.
Photosynthesis gene
Correct Answer:
Antibiotic resistance gene
Explanation:
Genes providing resistance to antibiotics such as ampicillin or tetracycline are commonly used as selectable markers.
3. A bacterial cell containing a plasmid with an ampicillin-resistance gene can grow on a medium containing:
A.
Ampicillin
B.
Only water
C.
A restriction enzyme
D.
DNA ligase
Correct Answer:
Ampicillin
Explanation:
The ampicillin-resistance gene allows transformed bacterial cells to survive and grow on medium containing ampicillin.
4. In the plasmid pBR322, which genes commonly act as selectable markers?
A.
Ampicillin-resistance and tetracycline-resistance genes
B.
Insulin and growth-hormone genes
C.
Chlorophyll and nitrogen-fixation genes
D.
Ribosomal RNA and transfer RNA genes
Correct Answer:
Ampicillin-resistance and tetracycline-resistance genes
Explanation:
pBR322 contains genes that provide resistance to ampicillin and tetracycline, allowing selection of transformed cells.
5. What happens to bacteria without a suitable selectable marker when grown on an antibiotic-containing medium?
A.
They are unable to grow
B.
They automatically form recombinant DNA
C.
They produce restriction enzymes
D.
They become viruses
Correct Answer:
They are unable to grow
Explanation:
Only cells carrying the appropriate antibiotic-resistance marker can survive on the corresponding antibiotic-containing medium.
6. If foreign DNA is inserted into the tetracycline-resistance gene of pBR322, the recombinant plasmid may cause the host cell to:
A.
Lose tetracycline resistance
B.
Lose all DNA
C.
Gain resistance to every antibiotic
D.
Stop containing a plasmid
Correct Answer:
Lose tetracycline resistance
Explanation:
Insertion of foreign DNA can disrupt the tetracycline-resistance gene, a process called insertional inactivation.
7. A selectable marker is useful because it allows scientists to distinguish between:
A.
Transformed and non-transformed cells
B.
DNA and RNA molecules
C.
Proteins and lipids
D.
Bacteria and fungi only
Correct Answer:
Transformed and non-transformed cells
Explanation:
Selectable markers help identify cells that have received the vector compared with cells that have not been transformed.
8. Which selectable marker would allow a transformed bacterium to survive in the presence of tetracycline?
A.
A tetracycline-resistance gene
B.
A gene for DNA ligase
C.
A gene for restriction enzyme production
D.
A gene for cell wall digestion
Correct Answer:
A tetracycline-resistance gene
Explanation:
A tetracycline-resistance gene produces the trait needed for bacterial survival on tetracycline-containing medium.
9. Insertional inactivation is directly associated with the disruption of a:
A.
Selectable marker gene
B.
Cell membrane
C.
Ribosome
D.
Culture medium
Correct Answer:
Selectable marker gene
Explanation:
Insertional inactivation occurs when foreign DNA is inserted into a selectable marker gene and interrupts its function.
10. Which observation indicates that bacteria have acquired an ampicillin-resistance marker?
A.
They grow on ampicillin-containing medium
B.
They fail to grow on nutrient medium
C.
They lose all plasmid DNA
D.
They digest the culture medium
Correct Answer:
They grow on ampicillin-containing medium
Explanation:
Growth on ampicillin-containing medium shows that the bacteria possess a functional ampicillin-resistance selectable marker.
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