Heterozygosity probabilities for normal relatives of isolated cases affected by incompletely penetrant conditions and the calculation of recurrence risks for their offspring. I. Autosomal dominant genes.

Heterozygosity probabilities P(het) for relatives of isolated cases produced by incompletely penetrant autosomal dominant genes and recurrence risks for their offspring, R = P(het).K/2, where K is the penetrance value, have been calculated in the literature for some simple particular situations. Bayes theorem and elements from the theory of finite difference equations enabled us to derive the heterozygosity probability for any individual belonging to a pedigree containing an isolated case affected with an incompletely penetrant autosomal dominant disorder. The generalized formula here derived is valid for most particular cases thus far studied in the literature.