A simple combinatorial method for calculating genetic risks.

A method is presented whereby genetic counsellors can calculate genetic risks in a wide variety of circumstances using only arithmetics. The method is general in that it can handle such information as gene frequency, mutation rate, mode of inheritance, penetrance, pedigree to which the consultand belongs, phenotype of the consultand and his relatives, biochemical findings, etc. Each of the possible combinations of genotypes which may be present in the pedigree is listed and considered in turn. The method consists of a series of simple steps leading mechanically to the right answer.