Seventeen of these were chosen for their proximity to 14 loci known to be involved in dog or human retinal diseases, or being expressed in the retina: ABCA4, CNGA1, GNAT1, GNGT1, NRL, PDC, PDE6A, PDE6D, PDEG, PRCD, RDS, RLBP1, ROM1 and SAG. The rest of the markers were selected to cover the whole of the autosomes at intervals of approximately 20 cM. Here, GNGT1 is linked to Abnormal retinal morphology.