Relationships between the individuals of a population have been previously studied from the point of view of prediction. Edwards (1967) suggested that the problem of detailed population structure could also be studied from the point of view of inference. Even where inferences of practical applicability cannot be made, such an approach can increase understanding of the relation between genealogical and genetic structure. In this paper we consider a specific problem which provides an introduction to the ideas and methods of genealogical inference. This is the problem of estimating the pairwise relationship between two individuals on the basis of their phenotypes at several loci. There is no theoretical problem in the extension from pairwise to joint relationship.