Probability of gene identity by descent: computation and applications.

Two genes at a given locus are identical by descent (IBD) if both have been inherited from a common ancestor. We present an algorithm for computing the probabilities of all IBD relationships among the genes of pedigree members. We show how to use these probabilities to calculate the probability of any combination of genotypes or phenotypes for the pedigree members. Applications to linkage analysis and genetic counseling are illustrated with examples. The algorithm also can be used to calculate the generalized kinship coefficients proposed by others.