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Things to do for Letitia Blennerhassett - DNA testing

  
  The results so far


DNA testing of Letitia Blennerhassett

So I have a theory that George Cashel is the son of Letitia Blennerhassett of Tarbert. There is lots of paper evidence for it, but no proof.

Here is my plan to use DNA to test the theory.

  
Stats:    DNA samples so far.    one-to-one DNA comparisons.
  


The plan

  1. Gather as many relations of Letitia Blennerhassett and George Cashel as possible.
  2. Get their DNA on Gedmatch (where anyone can compare DNA with anyone).
  3. Do one-to-one Autosomal DNA comparison of everyone with everyone.
  4. Build up a map.
  5. See what the map says.
  6. Include control matches to see what matches you could get by chance.

  7. Do all descendants of the 8 great-grandparents of Letitia Blennerhassett of Tarbert.
  8. Do all descendants of George Cashel.
  


The 8 great-grandparents of Letitia Blennerhassett.
From [Fuller, 1910].


  

The samples

We divide our samples into groups.



  


The results so far

  
  

Total segment matches (minimum segment 9)

Total segment matches in centiMorgans (cM).
Using minimum segment size = 9 cM.
Different sites use different minimum segment sizes. See autosomal DNA match thresholds.


DNA negatives:

The DNA positives make sense and match the family tree:

Much of the REV and CASH trees are now DNA-proved:

DNA positive matches across groups:

  

REV match with MUL and ED

  

ED and CASH match with JOHN

  

CASH match with MCA

  

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.


  

Look only at CASH with ED and REV


  

The best match for CASH so far

Under this metric (segment size 7 cM) we finally get a match of CASH with the main Blennerhassett family.
These are 3 borderline matches of CASH with ED. I don't think this proves the Letitia theory yet. But it is promising.

Could size 7-8 cM happen by chance?
Maybe. But could three of them happen by chance?

  

The best match for CASH so far:
The ED.9 and CASH.1 match.
ED.9 is a descendant of Mary Blennerhassett, sister of Rev. John.
CASH.1 is a descendant of Blennerhassett Cashel.
There is a 8.4 cM match on Chromosome 5.
Could this happen by chance?



The 2nd best match for CASH so far:
The ED.10 and CASH.1 match.
ED.10 is a descendant of Mary Blennerhassett, sister of Rev. John.
CASH.1 is a descendant of Blennerhassett Cashel.
There is a 7.5 cM match on Chromosome 21.
Could this happen by chance?



The 3rd best match for CASH so far:
The ED.7 and CASH.6 match.
ED.7 is a descendant of Elizabeth Blennerhassett, sister of Rev. John.
CASH.6 is a descendant of Blennerhassett Cashel.
There is a 7.4 cM match on Chromosome 19.
Could this happen by chance?


  

Total segment matches (minimum segment 5)

We reduce further.

Here is total segment matches using minimum segment size = 5 cM.


  

Look only at CASH with ED and REV

  

Largest segment in match

A simple metric:
Largest single segment in match, in cM.
Small segments can happen by chance. Large segments much less so.


  

Look only at CASH with ED and REV

  

Cousins v. Largest segment (REV and CASH only)

Let us analyse what largest segment we should expect for each level of cousins.
We number the cousins / relationships like this:

0.0 - siblings or parent/child
0.1 - uncle/aunt relationship
1.0 - 1st cousin (direct, no times removed).
1.1 - 1st cousin, once removed.
1.2 - 1st cousin, 2 times removed.
...
2.0 - 2nd cousin (direct, no times removed).
...


Our colour scheme will be:

  

Proven CASH cousins

Proven cousin relations of each other inside the CASH group:

And largest segment:

  

Proven REV cousins

Proven cousin relations of each other inside the REV group:

And largest segment:

  

Postulated REV and CASH cousins

This chart shows the postulated cousin relations of REV and CASH:

And largest segment:


  

Estimated MRCA

Gedmatch estimated number of generations to MRCA.



  

Look only at CASH with ED and REV

  


Cousins v. MRCA (REV and CASH only)

Look at proven cousins for CASH (proven from family tree):

Compare with Gedmatch estimated MRCAs for CASH (estimated from DNA):

The Gedmatch estimated MRCAs are a fairly good fit to the family tree. There are some false negatives.
  

Look at proven cousins for REV (proven from family tree):

Compare with Gedmatch estimated MRCAs for REV (estimated from DNA):

The Gedmatch estimated MRCAs are a fairly good fit to the family tree. There are some false negatives.
  


Conclusion - More samples needed

  

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