CRISPR/cas9 genome editing is used to insert an internal ribosome entry site 2 sequence, a FlpO recombinase gene, a bovine growth hormone polyA sequence, an attB site, a PGK/gb2 promoter-Neomycin resistance gene-PGK polyA cassette and an attP site following the STOP codon. The guide vector contained the Sncg guide RNA sequences designed for the endogenous stop codon and also a DNA sequence encoding a human codon-optimized Streptococcus pyogenes CRISPR associated protein 9 (SpCas9). Of note, the guide vector is designed so the SpCas9 protein is only expressed in embryonic stem (ES) cells and the SpCas9 DNA sequence does not integrate into the genome