Genetic Model THB ( T rait H eterogeneity with B oth Locus Heterogeneity and Gene-Gene Interaction). 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 Trait I, a locus heterogeneity model described by Li and Reich  is used, in which the trait is penetrant only when two copies of the high risk allele at one or both loci are present (in this case the B alleles for locus 2 and 3 are high risk). For Trait II, the ''diagonal'' genetic model first described by Frankel & Schork  and later by Li and Reich  is used. Two loci (2 and 3) are involved, each with two alleles (A and B), and the trait is penetrant only when exactly two copies of the high risk allele from either locus are present.