In CRISPR-Cas9 genome editing, the Cas9 protein acts as molecular scissors that cut DNA at specific sites, guided by a sequence known as __________.

In CRISPR‑Cas9 genome editing, the Cas9 protein cuts DNA at precise locations, and it is directed to those spots by a short RNA sequence called the guide RNA (gRNA). This gRNA contains a 20‑base pair segment that is complementary to the target DNA sequence, acting like a homing beacon. Cas9 binds the gRNA, and the complex scans the genome, binding to any DNA that matches the gRNA’s sequence and then making a double‑strand break. For example, if you want to delete a gene segment, you design a gRNA that matches a sequence just upstream of that segment; Cas9 will cut there, allowing the cell’s repair machinery to remove or modify the DNA. This precise targeting makes CRISPR a powerful tool for editing genes.