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 Shaded symbols indicate carriers of a disease or trait; open symbols are non-carriers. Inverse relationship between allele frequency and phenotypic effect, as postulated by Sewall Wright [10]. The arbitrary division between alleles with small (polygene), intermediate (oligogene) or large (major) effects is based on Morton [11]; λ, relative risk to sibs.