After Cas9 cuts the DNA, the cell repairs the break, and this repair process is used to introduce gene changes.

When Cas9 cuts the DNA, the cell tries to fix the break using its natural repair systems. One common repair method often causes small insertions or deletions, which can switch off a gene. Another repair method uses a template to copy new DNA into the cut site, allowing scientists to precisely insert or correct genes. By controlling these repair processes, CRISPR can knock out genes, delete sections, or fix mutations.