Selected MCQ

Current Question
In molecular cloning with a plasmid containing the lacZ α-fragment and a multiple cloning site, what color do colonies appear on X-gal/IPTG plates if the plasmid has an inserted DNA fragment?
  • A. Blue
  • B. White
  • C. Red
  • D. Green
Correct Answer: B
Explanation:
Insertion disrupts lacZ α-peptide, so β-galactosidase is not produced. Colonies remain white (no cleavage of X-gal), indicating successful insertion.
Related Question 1
Which plasmid-based technique is used to enrich and detect low-abundance mRNAs by reverse transcription into cDNA?
  • A. RFLP analysis
  • B. Northern blotting
  • C. RT-PCR (reverse-transcription PCR)
  • D. Affinity chromatography
Correct Answer: C
Explanation:
RT-PCR involves reverse-transcribing RNA to cDNA and then amplifying specific sequences by PCR. It is very sensitive for detecting low-abundance transcripts.
Related Question 2
Somatic cell nuclear transfer (SCNT) for reproductive cloning involves:
  • A. Injecting somatic cell DNA into a fertilized egg with its nucleus intact
  • B. Fusing a diploid somatic cell with an enucleated egg cell
  • C. Using only oocyte mitochondria from a donor
  • D. Cloning via binary fission
Correct Answer: B
Explanation:
SCNT (as in cloning Dolly the sheep) entails transferring the nucleus of an adult somatic cell into an enucleated oocyte, and then stimulating the resulting cell to divide as an embryo.
Related Question 3
During agarose gel electrophoresis of DNA, in which direction do DNA fragments migrate?
  • A. Toward the cathode (negative electrode)
  • B. Toward the anode (positive electrode)
  • C. DNA does not migrate in agarose
  • D. Toward the North Pole
Correct Answer: B
Explanation:
DNA has a negative charge (due to phosphate groups) and migrates toward the positively charged electrode (anode) when an electric field is applied.
Related Question 4
In a cloning vector, what is the purpose of including an antibiotic resistance gene?
  • A. To replicate the plasmid in host cells
  • B. As a selectable marker to identify transformed cells
  • C. To transcribe the cloned gene at high levels
  • D. To initiate DNA replication
Correct Answer: B
Explanation:
The antibiotic resistance gene allows selection: only bacteria that have taken up the plasmid (and express resistance) will grow on antibiotic-containing media.
Related Question 5
Genetically modified crops containing the Bt (Bacillus thuringiensis) toxin gene are resistant to:
  • A. Herbicides
  • B. Insect pests
  • C. Drought
  • D. Viral infection
Correct Answer: B
Explanation:
The Bt gene encodes an insecticidal protein. Plants expressing Bt produce a toxin that targets specific insect pests, providing built-in insect resistance.