In bacteria, which might be said to hold the original patent on the technology, CRISPR functions as an immune system. Bacteria that possess a “CRISPR locus” can incorporate snippets of DNA from viruses into their own genomes. They use these snippets, like mug shots, to recognize potential assailants. Then they dispatch CRISPR-associated, or Cas, enzymes, which work like tiny knives. The enzymes slice the invaders’ DNA at critical locations, thus disabling them.
