If the putative surrogate parents identified for a proband are true, it should be possible to classify them all as a single group (when only surrogate mothers or fathers exist) or to divide them into two groups. However, any attempt to group the surrogate parents could result in incompatibilities. Specifically, for a SNP that is heterozygous in the proband, an incompatibility occurs when two surrogate parents in the same group have different homozygous genotypes or if two surrogate parents in separate groups have the same homozygous genotype. Incompatibilities could also result from genotypes of more distant surrogate relatives. This happens when a surrogate parent is heterozygous, but data from her other surrogate relatives nonetheless suggest that the allele she shared with the proband has to be, say, the minor allele, which happens to be in contradiction with the data of the other surrogate parents. Indeed, the fact that any surrogate relatives, regardless of Erdös distance, could contribute to the phasing of each other also means that for individuals belonging to the main cluster in the haplotype-sharing graph, even a single
