Since the cone responses in Cnga3floxed-STOP mice remained robust, we moved forward with a second attempt to generate another reversible mouse model of achromatopsia by inserting a “floxed-STOP2886” (hereafter “floxed-STOP”) cassette in the intron between exon 5 and exon 6 of the Cnga3 gene using embryonic stem (ES) cell gene targeting (Figure 4). The gene discussed is CNGA3; the disease is achromatopsia.