To a geneticist, population structure signifies the relation between gene frequencies and genotype frequencies of individuals and pairs of individuals. The key concept is kinship, the probability that two alleles sampled in a specified way are identical by descent. If the alleles are in the same individual, kinship is called inbreeding, which is the same as kinship between the parents of that individual. Together with other coefficients that measure identity by descent in pairs of individuals, kinship and inbreeding determine the matching probability that two individuals sampled in a specified way have the same genotype. Kinship leads to inferences about the similarity and therefore (with less assurance) about the phylogeny of different populations and the optimal strategy for conserving variability in a species that may be endangered. Inbreeding leads to identifiable risks and inferences about the mutational load. Matching probabilities are the basis for DNA forensic science. The relationship of these concepts is the pons asinorum of population genetics. Much of the literature is marred by use of genetic distance and other surrogates for kinship, inefficient estimation, selection of extreme populations, and failure to allow for biases due to sample size and incompleteness of genealogies.

Kinship

It is possible to predict kinship from genealogies or migration, but the ultimate test is kinship bioassay.