Genetic Model THL ( T rait H eterogeneity with L ocus Heterogeneity). 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 Mendelian recessive genetic model is used, in which the trait is penetrant only when two copies of the high risk (B) allele are present. For Trait II, 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).