General Introduction to CRISPR/Cas：

CRISPR/Cas (CRISPR - Associated) is a technology that enables specific DNA modifications of target genes through the guidance of RNA - directed Cas nucleases. It is an acquired immune defense mechanism that has evolved in bacteria and archaea in response to the continuous attacks of bacteriophages and plasmids.
 
The CRISPR/Cas9 system derived from Streptococcus pyogenes is the most widely used as it only requires a single protein. In this system, a guide RNA (gRNA) with artificially optimized guiding functions directs the Cas9 nuclease to cleave double - stranded DNA at the target site paired with the gRNA, resulting in a double - strand break (DSB). Subsequently, the non - homologous end - joining (NHEJ) or homologous recombination (HR) mechanism within the organism repairs the DNA. This can lead to gene frameshift mutations, substitutions, or deletions. When template DNA is introduced, specific target fragments can also be inserted specifically.