Table 1. Brief characteristics of available molecular gene editing tools.

Tool	Mechanism	Advantages	Limitations
Recombinases
Cre-LoxP, Flp-FRT, Nigri/nox, Panto/pox and others	Induce recombination between target sites	Conditional gene modification possible	Difficult to find highly specific promoters, costly, and time consuming
Nucleases
ZFN	Recognize a specific site on DNA through zinc finger domains and introduce a double-stranded break	Gene targeting with good efficacy	Off-target activity, technical difficulty to create ZFN modules, difficulty to replace large fragments of DNA, high cost
TALENs	Cleave DNA between TALEN binding sites	A simpler and faster design compared to ZFN facilitated by the creation of “TALEN library”	Off-target activity, relatively large size complicates the delivery
CRISPR/Cas9	Cas9 is guided by RNA and cleaves DNA at designed sites	Ease of use: can be adapted to target any DNA site by changing the guide RNA	Relatively large size of the protein complex, off-target cleavage

ZFN: zinc finger nucleases; TALENs: transcriptional activator-like effector nucleases; CRISPR/Cas9: clustered regularly interspaced short palindromic repeat/CRISPR-associated protein 9.