The use of probability trees in genetic counselling

Calculation of genetic risks of persons who may be carriers of X‐linked recessive conditions or autosomal dominant diseases with incomplete or delayed penetrance often requires the use of Bayes' theorem. Available methods of computing such risks are often too difficult or too time‐consuming for clinicians to use routinely. Probability trees provide a rapid and simple graphical means of estimating genetic risks even in complex clinical situations. The use of probability trees is easily learned because the logic upon which they are based is inherent in their structure.