Humphrys genealogy

Genealogy research by Mark Humphrys.

Blennerhassett problem - DNA testing - CASH v. DAU



DNA testing - Cashel with the Baronets branch.
For background see DNA testing for the Blennerhassett problem.

This page is about the tests done to prove or disprove the theory of our descent from the Blennerhassett Baronets branch through a lost daughter.

On the very first sample (BART.1) the results said the Baronets theory is true. Our family is closely related to the Blennerhassett Baronets branch.



We compare individuals from the groups defined here.

This page will compare:


Total segment matches (minimum segment 9)

We start by considering total segment matches, using minimum segment size = 9 cM.
9 cM is generally considered significant.

We compare our family with the Blennerhassett Baronets family.

The results are even better than they look here

Is the BART.1 match evidence for the Letitia theory?

False positives: BUTLER match with CASH.1


The proof that the Baronets theory is true, May 2020

The following 15 cM match between our family and the Baronets family basically proved that the Baronets theory is true.
This match proved the Blennerhassett link on 26 May 2020, after 35 years of trying.

The match is between these two people:


The second great match, Oct 2020

On 18 Oct 2020, we got an even better match with the Baronets family, of 21 cM.

The match is between these two people:

Total segment matches (minimum segment 7)

Let us try (as some sites do) reducing the minimum segment size and looking at total segment matches.

Here is total segment matches using minimum segment size = 7 cM.


Largest segment in match

We now take a wider look at the data by showing for every match, what is the largest segment.
Largest single segment in match, in cM.
Small segments can happen by chance. Large segments much less so.


Estimated MRCA

If there is a segment over 5 cM, Gedmatch estimates the number of generations to Most Recent Common Ancestor (MRCA).
This is an estimate from the DNA, not from the family tree.
Gedmatch can give different estimates depending on the minimum segment length you pick. We use the closest estimate, which is the estimate given under minimum segment 5 cM.


Postulated cousins

Now we consider, under the Baronets theory, the postulated cousin relations of CASH with DAU.

How do we estimate the cousin numbers? This is difficult. We take the most likely theory, which is that we descend from the 1st Baronet. We assume George Cashel is somehow a grandson of the 1st Baronet. But depending exactly how he is a grandson, these cousin numbers could vary. e.g. If George Cashel is the natural son of the 2nd Baronet, then we have 3.1 and 4.0 cousinships with the 7th Baronet. If George Cashel is son of the 2nd Baronet's sibling, those become 4.1 and 5.0 cousinships.

Until we find out exactly how George Cashel descends, we will use the bigger numbers.

Here are the Gedmatch estimated MRCAs:

The pattern looks different to the postulated cousins. None of the 4th cousins match.
It does not at first look great.
But in fact, looked at a different way, the DNA is actually a pretty good fit with the postulated cousins:

Here are the largest segments:


Real cousins v. Postulated cousins

Let us write out the entire list of results for real cousins versus the same list for postulated cousins, separate into lists for each type of cousin, and sort the lists, to see if the postulated has the same pattern as the real.

Here are the lists, for each type of cousin, of largest segments for real cousins versus the same list for postulated cousins (for CASH crossed with DAU).
We start at "4.0" cousins (there are no closer living postulated cousins).


Conclusion - The Baronets theory looks true

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