CRISPR-mediated alb knockout. (A) Schematic representation of the alb locus. The gene consists of seven exons (introns are not drawn to scale). The mutation alb^b4 introduces a premature stop codon into exon 6. (B) The sequence of exon 6 (in capitals). The CRISPR target site, PAM motif and the alb^b4 mutation are indicated; the SNPs introduced into the donor DNA fragments are shown beneath the CRISPR target site. (C-F) Dorsal views of larvae at 5dpf: uninjected control wild type (C) and alb^b4 (D) larvae, and injected wild-type larvae with moderate (E) and good (F) alb knockout efficiency.

Homology-directed repair at the alb locus. (A) Donor DNAs used. The PCR fragments were also cloned into pGEM-T and injected as circular DNA molecules; the construct with the two CRISPR target sites is depicted. (B-D) Dorsal views of larvae 5dpf: uninjected alb^b4 control (B), low efficiency repair using linear donor DNA (C) and high efficiency repair using circular donor DNA (D). (E,F) Two examples of adult F₀ fish showing pigmented melanophores as a consequence of HDR in melanophore stem cells.