CRISPR-Cas9 gene editing complex. Illustration of the molecular structure of the CRISPR-Cas9 gene editing complex. The CRISPR-Cas9 protein is used in genome engineering to cut DNA (deoxyribonucleic acid). It uses a guide RNA (ribonucleic acid) sequence to cut DNA at a complementary site. The Cas9 protein is shown in blue. The guide RNA is red, and the double-strands of the DNA are yellow and pink. The target DNA strand is yellow, and the non-target DNA strand is pink. CRISPR (Clustered Regularly Interspersed Palindromic Repeats) is a bacterial adaptive immunity system.