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BioTechnology QUESTION #10622
Question 1
CRISPR-Cas9 gene editing achieves precise genome modification because:
  • Cas9 is an RNA polymerase that transcribes the guide RNA into a new gene
  • The guide RNA (gRNA) directs Cas9 nuclease to a specific genomic locus where it creates a double-strand break✔️
  • Cas9 methylates the target DNA sequence, silencing gene expression without cutting
  • The guide RNA acts as a ribosome to translate the edited gene directly
Correct Answer Explanation
CRISPR-Cas9 consists of: (1) a single guide RNA (sgRNA) with a 20-nt spacer complementary to the target DNA sequence, and (2) Cas9 nuclease, which binds the sgRNA and creates a blunt-ended double-strand break (DSB) adjacent to the PAM sequence (NGG for S. pyogenes Cas9). The DSB is repaired by NHEJ (creating insertions/deletions → gene knockout) or HDR (using a donor template → precise edit). Its programmability, efficiency, and precision revolutionised genome editing.