Potentials and limits of pairwise kinship analysis using autosomal short tandem repeat loci

At least in principle, most instances of complex kinship testing can be reduced to pairwise kinship cases involving two critical family members that either link or separate presumed sub-branches of a family. In the European population, the 34 short tandem repeats (STRs) currently used in forensic genetics are sufficiently powerful to allow assessment of disputed first and second but not lower degrees of pairwise blood relatedness. We provide estimates of the means and variances of marker-specific log-likelihood ratios, using large-sample approximation and assuming different scenarios of pairwise kinship analysis. These estimates allow power calculations to be performed for any combination of the available STRs. Since some of the markers considered are physically linked, chromosome-wide likelihood calculations in kinship cases other than parent–child duos (and trios) have to take the reduced rates of meiotic inter-marker recombination into account. We show by simulation that this requirement may be ignored when discriminating distant hypotheses about kinship, but that linkage may play an important role in the biostatistical analysis of more intricate cases.