alleles identical by descent (IBD). Individuals sharing two alleles IBD at every locus are either monozygotic twins, or the pair is actually a single sample processed twice. Individuals sharing zero alleles IBD at every locus are unrelated. Individuals sharing one allele IBD at every locus are parent-child pairs. On average, siblings share zero, one, and two alleles IBD at 25%, 50%, and 25% of the genome, respectively. Using these data, the proportion of loci sharing one allele IBD (the Z1 column) by the proportion of loci where individuals share zero alleles IBD (column Z0) can be plotted and points color coded by the relationship type. For clarity, this plot can be restricted to points where the overall kinship coefficient is ≥ 0.05, as most of the individuals where kinship ≤ 0.05 will be unrelated. This will produce a plot as shown in Figure 4. Detailed instructions on producing this graphic using R [20] can be found online [21]. If it is believed that pedigree records obtained through the original data are accurate, then a point out of place (e.g., points colored as unrelated showing up where most of the parent-offspring pairs cluster) would be indicative of either nonpaternity, adoption, sample
