How does the CRISPR-Cas9 system achieve precise genome editing?

CRISPR‑Cas9 works by using a short piece of RNA that matches a target DNA sequence, guiding the Cas9 enzyme to that exact spot. Cas9 then cuts the DNA double‑strand at that location, creating a break. The cell’s own repair machinery closes the break, and scientists can supply a new DNA piece that the cell uses to fill the gap, inserting or deleting genes. Because the guide RNA is very specific, the cut happens only at the chosen site, making the edit precise. For example, researchers can remove a faulty gene in a mouse eye by cutting it out and inserting a healthy copy, restoring normal vision.