An FRT site and loxP site flanked neomycin resistance gene cassette was inserted into intron 1 and exon 1 was replaced with a version with two engineered mutations: a silent TTC>TTT mutation to aid genotyping and an AAA deletion to create an allele coding for a peptide with a K153 deletion. This deletion emulates one causing variable retinal phenotypes in human patients. The neo cassette was removed through flp-mediated recombination. (J:237869)