ESTIMATION OF RELATEDNESS IN NATURAL-POPULATIONS USING HIGHLY POLYMORPHIC GENETIC-MARKERS

This report addresses 3 important questions in population biology: 1), Is it possible to determine the actual kinship between individuals taken at random from a natural population? 2), Is it possible to estimate an average degree of kinship in a population in terms of the probability that 2 individuals drawn at random are related? 3), Is it possible to estimate a population's family structure in terms of the number and the relative size of the different families? To answer these questions the estimation of kinship between 2 individuals is first considered. To do this, identity probabilities, based upon 2 sets of assumptions concerning the genetic markers used, were derived for different cases of kinship. The use of VNTRs (variable number of tandem repeats) shows that for multilocus probes, all distributions of identity broadly overlap even when the number of loci is about 20. Therefore by VNTRs alone, it is difficult to define the true kinship between 2 individuals when only their DNA fingerprints are compared. More accurate estimations can be achieved with monolocus probes. However, to estimate a population's structure or the average degree of kinship between individuals, it is not necessary to identify precisely each individual sampled, but rather, only to determine whether individuals are related or not. For this, it is necessary to define a threshold identity value which depends on the common patterns that can be observed between unrelated individuals. Below this value, individuals are considered to be unrelated and, above it, they are considered to be related. Finally, a sequential sampling procedure is proposed.