Genetic Information Given by a Relative

SUMMARY What genetic information concerning an individual can be provided by the knowledge of the genetic make-up of one of his relatives? In general, the well-known of is not sufficient to solve the problem. It is necessary to use a more complete measure of kinship, the set of nine condensed identity coefficients. This article reviews these coefficients and their use to establish equations which give the (i.e. the set of probabilities of the various genotypes) of an individual, given the genotype of one of his relatives and the gene structure of the population. When the ancestry network is simple enough, these equations may be put in a form in which only the coefficient of kinship appears. But the conditions for such a simplification are restrictive: not only must both relatives not be inbred, but also the kinship between them must be unilineal.