CRISPR-Cas9 technology is primarily derived from a natural defense mechanism found in _______ that allows them to recognize and eliminate viral DNA.

CRISPR‑Cas9 technology comes from a natural defense system that bacteria use to fight viruses. In bacteria, small pieces of viral DNA are stored in a special region called CRISPR, and a protein called Cas9 reads those pieces and cuts matching viral DNA. The bacteria can then destroy the invading virus before it takes over. For example, a bacterium that has been infected by a virus will keep a short snippet of the virus’s DNA; when the same virus attacks again, Cas9 uses the stored snippet to find and cut the virus’s genome. This bacterial “memory” system is what scientists adapted into the CRISPR‑Cas9 tool we use for gene editing.