A conditional allele in which the second of the gene's 10 exons is flanked by loxP sites was generated using a variation of CRISPR/Ca9 technology employing paired Cas9 nickase (Cas9n) RNA with associated sgRNAs and a single DNA template containing loxP sites flanking exon 2. Cre recombinase treatment of genomic DNA from an F1 pup inheriting the PCR-verified mutation demonstrated correct excision of exon 2.