Chapter Exam

Chapter 3: Gene Cloning — Online MCQ Test

Q: Which enzyme is used to cut DNA at specific recognition sequences during gene cloning?

Answer: B. Restriction endonuclease — Restriction endonucleases recognize specific DNA sequences and cut DNA at or near those sites. They are essential tools in gene cloning.

Q: A plasmid used in gene cloning is best described as:

Answer: B. A small circular extrachromosomal DNA molecule — Plasmids are small, circular, double-stranded DNA molecules found outside the bacterial chromosome. They can replicate independently and are commonly used as cloning vectors.

Q: In gene cloning, the DNA fragment to be cloned is commonly called the:

Answer: B. Insert — The foreign DNA fragment introduced into a vector is called the insert. The vector carries this insert into the host cell.

Q: Why are the same restriction enzyme often used to cut both the vector and the foreign DNA?

Answer: A. To produce compatible ends for joining — Cutting the vector and insert with the same restriction enzyme often produces complementary sticky ends. These compatible ends can base-pair and be sealed by DNA ligase.

Q: A restriction enzyme produces staggered cuts in DNA. The ends produced are called:

Answer: B. Sticky ends — Staggered cuts leave short single-stranded overhangs called sticky ends. These ends can pair with complementary sequences.

Q: A plasmid vector has a single EcoRI site within a tetracycline resistance gene and an ampicillin resistance gene elsewhere. If foreign DNA is inserted at the EcoRI site, which phenotype is expected for recombinant colonies?

Answer: A. Ampicillin resistant and tetracycline sensitive — Insertion within the tetracycline resistance gene disrupts that marker, making cells tetracycline sensitive. The ampicillin resistance gene remains functional, so cells are ampicillin resistant.

BIOTECHNOLOGY · Grade 12 · CBSE(NCERT)

Practice Chapter 3: Gene Cloning with a free chapter-wise online MCQ test for CBSE(NCERT) Grade 12 BIOTECHNOLOGY. This chapter covers: Gene Cloning Restriction Enzymes DNA Ligase Recombinant DNA Transformation DNA Replication Host Cell Plasmid Cloning Gene Amplification Recombinant Technology. AI-generated questions from basic to board-exam level, with instant results and explanations.

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Chapter 3: Gene Cloning — Important Questions & Answers (FAQ)

Frequently asked questions from CBSE(NCERT) Grade 12 BIOTECHNOLOGY — Chapter 3: Gene Cloning, with answers and explanations. These are sample questions; the exam has its own separate question set.

Which enzyme is used to cut DNA at specific recognition sequences during gene cloning?

A. DNA ligase
B. Restriction endonuclease ✓
C. DNA polymerase
D. RNA polymerase

Answer: B. Restriction endonuclease
Restriction endonucleases recognize specific DNA sequences and cut DNA at or near those sites. They are essential tools in gene cloning.

The enzyme DNA ligase is mainly used in recombinant DNA technology to:

A. Cut DNA into fragments
B. Join DNA fragments by forming phosphodiester bonds ✓
C. Unwind the DNA double helix
D. Synthesize RNA from DNA

Answer: B. Join DNA fragments by forming phosphodiester bonds
DNA ligase joins DNA fragments by sealing nicks in the sugar-phosphate backbone. It forms phosphodiester bonds between adjacent nucleotides.

A plasmid used in gene cloning is best described as:

A. A linear RNA molecule found in viruses
B. A small circular extrachromosomal DNA molecule ✓
C. A protein that cuts DNA
D. A chromosome present only in plant cells

Answer: B. A small circular extrachromosomal DNA molecule
Plasmids are small, circular, double-stranded DNA molecules found outside the bacterial chromosome. They can replicate independently and are commonly used as cloning vectors.

In gene cloning, the DNA fragment to be cloned is commonly called the:

A. Vector
B. Insert ✓
C. Primer
D. Marker

Answer: B. Insert
The foreign DNA fragment introduced into a vector is called the insert. The vector carries this insert into the host cell.

Why are the same restriction enzyme often used to cut both the vector and the foreign DNA?

A. To produce compatible ends for joining ✓
B. To destroy all unwanted DNA
C. To prevent plasmid replication
D. To convert DNA into RNA

Answer: A. To produce compatible ends for joining
Cutting the vector and insert with the same restriction enzyme often produces complementary sticky ends. These compatible ends can base-pair and be sealed by DNA ligase.

A restriction enzyme produces staggered cuts in DNA. The ends produced are called:

A. Blunt ends
B. Sticky ends ✓
C. Replication ends
D. Terminator ends

Answer: B. Sticky ends
Staggered cuts leave short single-stranded overhangs called sticky ends. These ends can pair with complementary sequences.

Which order correctly represents the major steps in a basic gene cloning experiment?

A. Transformation, ligation, restriction digestion, selection
B. Restriction digestion, ligation, transformation, selection ✓
C. Selection, transformation, ligation, restriction digestion
D. Ligation, selection, restriction digestion, transformation

Answer: B. Restriction digestion, ligation, transformation, selection
The vector and insert are first cut with restriction enzymes, then ligated to form recombinant DNA. This is followed by transformation into host cells and selection of transformants.

A plasmid vector has a single EcoRI site within a tetracycline resistance gene and an ampicillin resistance gene elsewhere. If foreign DNA is inserted at the EcoRI site, which phenotype is expected for recombinant colonies?

A. Ampicillin resistant and tetracycline sensitive ✓
B. Ampicillin sensitive and tetracycline resistant
C. Sensitive to both antibiotics
D. Resistant to both antibiotics

Answer: A. Ampicillin resistant and tetracycline sensitive
Insertion within the tetracycline resistance gene disrupts that marker, making cells tetracycline sensitive. The ampicillin resistance gene remains functional, so cells are ampicillin resistant.

A student ligates a foreign DNA insert into a plasmid but forgets to treat the cut vector to reduce self-ligation. After transformation, many colonies grow on the antibiotic plate. Which conclusion is most accurate?

A. All colonies must contain recombinant plasmids
B. Some colonies may contain self-ligated vector without insert ✓
C. No colony can contain a plasmid
D. Antibiotic selection alone proves insert orientation

Answer: B. Some colonies may contain self-ligated vector without insert
Antibiotic selection shows that cells contain a plasmid with a functional marker, but it does not always prove that the insert is present. Self-ligated vector can also transform cells and grow.

Which of the following combinations would most specifically help identify recombinant colonies rather than merely transformed colonies?

A. Antibiotic selection plus screening for insertional inactivation ✓
B. Growth in nutrient broth without antibiotic only
C. Using DNA ligase without any vector
D. Selecting cells that failed to take up plasmid DNA

Answer: A. Antibiotic selection plus screening for insertional inactivation
Antibiotic selection identifies transformed cells, while insertional inactivation or similar screening helps distinguish recombinants from non-recombinant plasmid carriers. Both are often needed.

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Chapter 2: Host Vector System

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Chapter 4: Applications of Recombinant DNA Technology