Figure 1.

(a) Illustration of the common variant/common disease and multilocus/multiallele hypotheses (see text for details). Shaded symbols indicate carriers of a disease or trait; open symbols are non-carriers. (b) 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_S, relative risk to sibs.