Genetic Analysis of Complex Traits
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The analysis of traits and disorders that exhibit a straightforward Mendelian genetics, based on the kind of major gene models that are easy to set up in computer programs such as LINKAGE (1 ), has been enormously successful in facilitating identification of the genes responsible. These monogenic models typically use two alleles to represent the trait locus, one allele predisposing to development of the disease or disorder and the other allele showing a normal phenotype, with a penetrance parameter that is specified for each genotype (see Table 1 ). Family studies using these techniques have led to the localization of many hundreds of single gene disorders (2 ) and an appreciable fraction of those localized have been positionally cloned.
Table 1 Modeling the Expression of a Trait Phenotype
|
Parameter |
Meaning |
|---|---|
|
P t |
Trait allele frequency=1−Pn |
|
f tt |
Penetrance of the t/t genotype = pT |tt |
|
f tn |
Penetrance of the t/n genotype = pT |tn |
|
f nn |
Penetrance of the n/n genotype = pT |nn |
|
f t |
Penetrance of the t allele = pT |t |
|
f n |
Penetrance of the n allele = pT |n |
