Mean genome-wide allelic mismatch rates for each pair of individuals (blue), as well as intra-individual comparisons (red), are shown. We selected one read per individual at random at each targeted SNP (using all 1,233,013 targeted sites). Monozygotic twins (or intra-individual comparisons) are expected to have a value one-half as large as unrelated individuals; first-degree relatives, halfway between monozygotic twins and unrelated individuals; second-degree relatives, halfway between first-degree relatives and unrelated individuals; and so on. The presence of inbreeding also serves to reduce the rate of mismatches. For 4/A and 5/B, we can eliminate a grandparent–grandchild relationship because both died as children, and the lack of long segments with IBD sharing on both homologous chromosomes implies that they are not double cousins (the few ostensible double-IBD stretches are probably a result of inbreeding (Supplementary Information section 2)). Thus, we can conclude that they were either uncle and niece (or aunt and nephew) or half-siblings. Bars show 99% confidence intervals (computed by block jackknife).