Any of various techniques for making precise, site-specific changes in the base sequence of the DNA of an organism. Each uses an engineered DNA-binding construct to seek out the target sequence, and a nuclease enzyme to cut the two strands of the DNA double helix at the required site. By exploiting the cellular DNA repair mechanisms, small inserts or deletions can be made at a single site, often causing inactivation (knockout) of the affected gene. Further, by cutting at two sites, larger inversions or deletions can result; and when a donor DNA template or transgene is introduced with the editing module, entire genes can be corrected or replaced. Genome editing is performed chiefly for genetic research, but increasingly is seen as a valuable technique to correct harmful mutations during gene therapy, and to engineer transgenic organisms, especially in animal and plant breeding. Several different technologies are used, including CRISPR-Cas9, zinc finger proteins, TALENs, and Cre/loxP recombination.