Classifying, identifying and enumerating arbitrary relationships

In studies of human genetic isolates, or pedigrees, it is often required to examine the relationships that exist between two individuals in the isolate. This may be of interest in connection with inbreeding, or in its own right, for example in the study of mating patterns. A scheme is developed for classifying any relationship between two individuals in a pedigree as a pair of integers. Relative to a common ancestor, the first integer counts the level of the relationship and the second the difference in generation between the individuals. The scope of this scheme is broad enough to encompass cases of multiplicity of relationships and half-relationships. An algorithm for counting the number of times a given relationship occurs between two individuals is outlined. This algorithm assumes that recursion is possible and that the information on the pedigree is stored in such a way that the parents of an individual can be readily traced. It has been implemented in Algol 68 and in C. The method is illustrated by an example from the complex Samaritan pedigree.