CRISPR/CAS9-Mediated Gene Editing in Human Gametes: A Review

Gene editing exploits endogenous DNA repair pathways to introduce precise modifications into the genome. The CRISPR system was first identified in Escherichia coli (1987) and, based on Cas protein architecture, is divided into Class I (types I, III, IV) and Class II (types II, V, VI). The widely adopted CRISPR/Cas9 system comprises a guide RNA (gRNA) and the Cas9 endonuclease, which orchestrate genome editing through a tripartite mechanism: target sequence recognition via gRNA binding to a complementary DNA site adjacent to a protospacer adjacent motif (PAM), double-stranded DNA cleavage by two nuclease domains (RuvC cleaving the non‑target strand and HNH the target strand), and repair of the resulting break by cellular pathways. This approach has been applied to in vitro fertilization-derived embryos and meiotically developing oocytes to disrupt or correct genes, offering potential for eliminating heritable diseases. However, concerns remain regarding off-target effects that introduces unwanted genetic mutations, necessitating improved specificity and ethical scrutiny.