In 2012, Jennifer Doudna and Emmanuelle Charpentier, a molecular biologist and microbiologist, respectively, were the first to propose that the bacterial CRISPR/Cas9 system could be used as a programmable toolkit for genome editing in humans and other animal species. For their path breaking work, they were eventually awarded the Nobel prize in chemistry in 2020. Another breakthrough achieved the synthesis of single gRNA (sgRNA) which combines the role of crRNA and tracrRNA into a single molecule by fusing them together with a linker. The mechanism of CRISPR/Cas-9 genome editing contains three steps, recognition, cleavage, and repair summarized in Figure . The designed sgRNA directs Cas9 and recognizes the target sequence in the gene of interest through its 5ʹcrRNA complementary base pair component. The Cas9 protein remains inactive in the absence of sgRNA. The Cas9 nuclease makes doublestranded breaks (DSBs) at a site 3 base pair upstream to PAM. A short 2-5 base-pair length sequence, PAMs are conserved DNA sequences downstream to the cleavage site and its size varies depending on the bacterial species. Once Cas9 has found a target site with the appropriate PAM, it triggers local DNA melting followed by the formation of RNA-DNA hybrid. Then, the Cas9 protein is activated for DNA cleavage. Finally, the DSB is repaired by either non-homologous end joining (NHEJ) or homology-directed repair (HDR) cellular mechanisms. The NHEJ pathway repairs DSBs in DNA by directly ligating through an enzymatic process without the need for an exogenous homologous DNA, which means a DNA strand with similar sequence that can act as a template. The NHEJ mechanism can also introduce insertion or deletion (indels) of specific sequences at the joining ends. The other route of repair, the HDR pathway, is commonly found in bacterial and archaeal cells, while the NHEJ pathway is more common in a eukaryotic domain. The HDR process, although more complex than NHEJ, uses a homologous DNA template. The homologous DNA template has homology to the adjacent sequences surrounding the site of cleavage to incorporate new DNA fragments. The template guides the repair process and lowers the possibility of errors. Since there is no insertion or deletion of nucleotide sequences, the HDR pathway maintains uniformity in the size of the resulting double-stranded DNA (dsDNA), unlike NHEJ. 58