Conventional Research
The Robert Blair - Isabella Rankin line is one of the most researched line in the BSGR. Thirty-six past and present members claim to descend from this line. The line predates the American Revolution.

Robert and Isabella had 7 sons: Matthew, David,  John, William, James, Robert,  and Joseph.

DNA Testing
We have six paricipants who believe they descend from the Robert Blair - Isabella Rankin line. Four descend through son Matthew, while two descend through son David. The four who descend from Matthew descend through three different sons: Jacob, Isaac, and Adam.

All six participants tested at least 25 markers. The number of mismatches each had with others is shown in the following table:

Three participants tested at 37 markers. The number of mismatches each had with others is shown in the following table:

The actual marker values for each participant are shown in the table below.

The diagram below show the pedigrees of the six participants based on conventional research.

 

Conclusions
Participants #5328 and #18895 match 25/25 but share a common ancestor in 3 transmission events. With only 3 such transmission events you expect to have a perfect match.

Participant #5328 and #18895 match the other four participants on only 7 of 25 markers. The probability of mismatching on 18 of 25 markers and sharing a common ancestor within 24 generations is less than 0.00001%.

There is no way #5238 or #18895 can share a common ancestor with either #6086, #9084, #26521, or #129948.

The results for the other four participants are still unclear. Participant #9084 seems to be causing most of the confusion.

Participants #9084 and #6086 are believed to share a common ancestor (George Oscar Blair and Clarissa Torrey). There are 7 transmission events (opportunities for a mutation) between the two participants. The expected number of mutations (marker differences) in 7 transmission events is 0.7. The probability of 3 mutations in only only 7 transmission events is less than 3.0%.

At the 37 marker level there about a 50% chance that #9084 and #129448 both descend from Robert and Elizabeth. There is about a 15% probability that #9084 and #26521 both descend from Robert and Elizabeth.

 Participants #6086, #26521, and #129948 almost certainly share the common ancestor Robert.