Halford S, Freedman MS, Bellingham J, Inglis SL, Poopalasundaram S, Soni BG, et al. (March 2001). "Characterization of a novel human opsin gene with wide tissue expression and identification of embedded and flanking genes on chromosome 1q43". Genomics. 72 (2): 203–208. doi:10.1006/geno.2001.6469. PMID11401433.
Halford S, Freedman MS, Bellingham J, Inglis SL, Poopalasundaram S, Soni BG, et al. (March 2001). "Characterization of a novel human opsin gene with wide tissue expression and identification of embedded and flanking genes on chromosome 1q43". Genomics. 72 (2): 203–208. doi:10.1006/geno.2001.6469. PMID11401433.