Genetic Model THO ( T rait H eterogeneity O nly). The penetrance tables for Trait I and Trait II are presented. Cell values indicate penetrance level, or the probability of having the trait, given the corresponding multilocus genotype. For each of the two traits, a Mendelian recessive genetic model is used, in which the trait is penetrant only when two copies of the high risk (B) allele are present. The penetrance (x) is constrained by the desired overall disease prevalence to be simulated (0.001, 0.01, 0.05 or 0.15).