Genome editing by zinc finger nucleases. (A) A zinc finger nuclease consisting of DNA recognition domains and an endonuclease are designed to recognize a specific site near a mutation. (B) The nuclease domains introduce a double-strand break into the DNA. (C) A wild-type sequence in introduced into the cells and used as the template for a cellular repair process, homologous recombination. (D) The mutant sequence is corrected. Adapted from