Copyright information:Taken from "Complex genetic diseases: controversy over the Croesus code"Genome Biology 2001;2(8):comment2007.1-comment2007.8.Published online 1 Aug 2001PMCID:PMC138948.Copyright © 2001 BioMed Central Ltd The diagram shows the diversity of disease loci in Mendelian forms of blindness. A rough relationship between tissue and physiological complexity and the number of identified disease loci can be discerned. Data are from the Online Mendelian Inheritance in Man [30] and RetNet [31] databases. RP, retinitis pigmentosa; Usher, Usher syndrome; BBS, Bardet-Biedl syndrome.