Empowering sibship analyses with reference pedigrees

In sibship analysis, the usual comparison of an alleged (test) sibling's short tandem repeat (STR) types with those of a reference sibling may prove inconclusive. Increasing the number of examined STR loci may not change sibship probabilities very much. We increased the number of verified reference siblings to resolve problematic cases of alleged sibship.

(A) Ten paternity cases were chosen in which there were three highly probable children of each alleged father. Pairs of the alleged father's children were analyzed for full sibship. The test sib with the lowest likelihood of sibship was reanalyzed by a comparison with two reference siblings combined. (B) Five problematic sibship cases are presented to demonstrate how two-person reference pedigrees can improve diagnosis over tests using one reference person.

(A) Two-person pedigrees exponentially increased sibship probabilities of true siblings above those produced by one reference person. (B) In problem cases, reference pedigrees provided data that: (1) statistically verified some alleged sibships in which analyses using one reference person yielded inconclusive results, (2) allowed exclusion of some alleged sibships, or (3) suggested alternate blood relationships to the alleged one.

Use of reference pedigrees often resolves sibship questions left unsettled by tests using reference individuals. Adding reference relatives is a far more powerful analytical strategy than adding test loci. Whenever possible, verified blood relatives should be incorporated into a reference pedigree to retest an alleged sibling whose initial results were unclear.