Selected MCQ

Current Question
In the CRISPR-Cas9 system, which component confers sequence specificity to target DNA?
  • A. Cas9 enzyme
  • B. Guide RNA (gRNA)
  • C. PAM sequence
  • D. DNA ligase
Correct Answer: B
Explanation:
The guide RNA (gRNA) base-pairs with the target DNA sequence, directing Cas9 to the specific genomic locus, where Cas9 then induces a double-strand break.
Related Question 1
Which assay would you use to detect and quantify a specific DNA sequence in a sample?
  • A. ELISA
  • B. Southern blot
  • C. Western blot
  • D. Gram staining
Correct Answer: B
Explanation:
A Southern blot uses a DNA probe to hybridize with a specific DNA sequence immobilized on a membrane, allowing detection of that sequence in the sample.
Related Question 2
In Southern blotting, what type of probe is used to detect specific DNA sequences?
  • A. DNA probe labeled with a reporter
  • B. RNA probe labeled with a reporter
  • C. Protein probe labeled with antibody
  • D. Carbohydrate probe
Correct Answer: A
Explanation:
Southern blot uses a labeled single-stranded DNA (or RNA) probe complementary to the target DNA sequence, hybridizing to it on the membrane.
Related Question 3
What is the genotype of a person with blood type O in the ABO system?
  • A. IᴬIᴬ or Iᴬi
  • B. IᴮIᴮ or Iᴮi
  • C. ii
  • D. IᴬIᴮ
Correct Answer: C
Explanation:
Type O blood has no A or B antigen and is genotypically ii (both alleles are the recessive i).
Related Question 4
A one-nucleotide insertion in the coding sequence of a gene will most likely result in which type of mutation?
  • A. Missense mutation
  • B. Nonsense mutation
  • C. Frameshift mutation
  • D. Silent mutation
Correct Answer: C
Explanation:
Inserting one nucleotide shifts the reading frame of the codons (frameshift), altering all downstream amino acids and usually disrupting function.
Related Question 5
Which of the following components is *not* required for a standard PCR reaction?
  • A. Template DNA
  • B. DNA polymerase
  • C. Primers
  • D. DNA ligase
Correct Answer: D
Explanation:
PCR requires a thermostable DNA polymerase, primers, dNTPs, and template DNA. DNA ligase is not needed because PCR does not splice DNA fragments.