How does CRISPR work?

CRISPR is a gene editing system identified in bacteria and archaea, where it functions as a defence against viral attack. Short nucleic acid sequences are captured from invading pathogens and integrated into CRISPR loci between repeat sequences. Small RNAs produced by transcription of these loci can then guide a set of endonucleases to cleave the genomes of future invading pathogens, thereby disabling their attacks. Scientists can leverage the CRISPR mechanism in the lab using a guide RNA (gRNA) for targeting and Endonuclease (Cas9), often referred to as "Molecular Scissors", to trigger a double-strand break in the cell DNA at a targeted location, enabling knockout or knockin of gene function.