in the study using estimates of the alleles that are shared identity by descent (IBD). Two alleles are shared IBD when they are identical copies of the same ancestral allele. Mendel’s laws of inheritance can be used to estimate the probability that two family members share 0, 1, or 2 alleles IBD. For example, monozygotic twins will always share two alleles IBD with probability 1, whereas siblings will share 0 alleles with probability [1/4], one allele with probability [1/2], and two alleles with probability [1/4] (see examples in Fig. 3). This estimation can be generalized to any relatives [63] and to genome wide alleles that are IBD. The analysis is computationally very intensive and estimates the proportion of alleles that are IBD using frequencies of alleles that are the same, also known as alleles identity by state or IBS [63]. The estimates can be used to quantify the degree of relatedness among subjects in the study as shown in Table III [64], and can identify repeated samples, as well as unknown relations. If the study includes subjects with known familial relations, the analysis can compare expected and observed relations in the sample as a quality control metric. The popular software
