CRISPR/Cas9 technology generated a 1652 bp deletion from chr1:139,254,836-139,256,488, plus a deletion of two additional cytosines, deleting the entire first exon of the B isoform (Crb1-B) and the promoter region. This abolishes the B isoform while preserving other isoforms including the A isoform. (J:293375)