Short tandem repeat-based identification of individuals and parents

Estimation of short tandem repeat (STR) multilocus genotype frequencies for the identification of individuals and estimation of allele frequencies for parentage assignment both depend on (a) testing a lot of loci, (b) high levels of polymorphism at each locus tested, and (c) independence among alleles. Independence is critical, because the estimation of multilocus genotype and gamete frequencies is based on multiplying individual allele frequencies to produce a composite frequency estimate. Independence among alleles at a locus is known as Hardy-Weinberg equilibrium, whereas allelic independence between loci is known as linkage equilibrium. The frequency at which individual identification may be declared is a matter of opinion, as there is no scientific way to specify certainty based on frequency estimates. Similarly absolute assignment of parentage is impossible in theory; in practice it is more difficult than individual identification, because only half as much information is available (gamete vs genotype frequency) and because mutation may confound parentage analysis.