Table 1.

Identification of variant IBD status conditional on chromosome

	0 IBD chromosome region	1 IBD chromosome region	2 IBD chromosome regions
Both siblings are homozygous minor allele	4 non-shared alleles	1 shared and 2 non-shared alleles	2 shared alleles
One homozygous minor allele and one heterozygote	3 non-shared alleles	1 shared and 1 non-shared alleles	N/A
Both siblings are heterozygous	2 non-shared alleles	Ambiguous configuration	1 shared allele

Assuming chromosome region IBD status is known, the number of shared and non-shared alleles can be inferred for all but one configuration of genotypes (shaded cell).