CRISPR-Cas9, a novel targeted genome-editing technique, mainly contains two components: a guide RNA (gRNA or sgRNA) and a CRISPR-associated endonuclease (Cas9 protein). Now gene editing--disrupt, delete, correct or insert can be achieved through different expression systems, Cas9 Enzymes and markers. Cas9-mediated genetic perturbation is simple and scalable, empowering researchers to elucidate the functional organization of the genome at the systems level and establish causal linkages between genetic variations and biological phenotypes.