LETITIA

DNA testing - inside the Letitia 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 Letitia Blennerhassett of Tarbert.

The results say that the Letitia theory is not true. However the results on this page are still good.
As part of the testing, we proved many lines inside the known Letitia Blennerhassett tree.

Groups

We compare individuals from the groups defined here.

This page will compare:

LETITIA v LETITIA

Proven cousins

First, we lay out the known cousin relationships (known from the family tree) of people inside this branch.
Then we can compare DNA results to their known cousin relationship.

Inside LETITIA, we have only done cousin numbers for ED and REV.
Everyone here is proven related. Common ancestor is Edward Blennerhassett of Rossbeigh (born 1705).

There are three groups, representing three children of Edward Blennerhassett of Rossbeigh (born 1705).
To get cousin numbers for the Clifford line we assume Mary Blennerhassett is grandmother of John Clifford.

Total segment matches (minimum segment 9)

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

We include male-line and female-line relations of Letitia Blennerhassett of Tarbert.
So not everybody is related to everybody.

We get false negatives:

There are many false negatives.
Some of the people are related, but with common ancestor Edward Blennerhassett of Rossbeigh (born 1705). That far back, you get a lot of false negatives.

The DNA positives make sense and match the family tree:

GOD 1 and 2 really are known that closely related.
In the male-line, there are three groups, representing three children of Edward Blennerhassett of Rossbeigh (born 1705).
Descendants of Elizabeth Blennerhassett: ED 2, 7 and 8 really are known that closely related. ED 11 and 3 really are known that closely related.
Descendants of Mary Blennerhassett: ED 4, 5, 9, 6 and 10 really are known that closely related.
Descendants of Rev. John Blennerhassett: REV 9, 15, 6, 7 and 8 really are known that closely related. REV 12 and 11 really are known that closely related. REV 14, 4 and 2 really are known that closely related. REV 10 and 1 also should form another group.
Even inside REV, REV.13 is so far along a different line from the others that there is no match. But there is a match with ED.

Quite a bit of the Blennerhassett tree is now DNA-proved:

The links inside the two ED groups and inside the REV group prove a lot of the Blennerhassett tree.
There are also links across those 3 groups (REV and the two ED groups). The strongest match is 16.2 cM and there are other significant matches. The 16.2 cM match is between two people who are 6th cousins once removed.
DNA is connecting the descendants of 3 different children of Edward Blennerhassett (born 1705). DNA is confirming the Edward Blennerhassett descent.
Between these matches on Gedmatch, and other matches on Ancestry, quite a bit of the Blennerhassett tree below "Black Jack" is now DNA-proved.
Search for DNA proven lines in my tree (see the Blennerhassett section).

GOD and MUL are not related to ED, but they are related to REV.

We have a remarkably strong match of MUL with REV.
We have 17.6 cM and 18.9 cM matches of siblings REV 14 and 4 with MUL. They are 7th cousins, no times removed. You have to go back to two different children of William Mullins (born 1691). This makes a match fairly amazing.
Both sides have Anglo-Irish Munster ancestry, and we can find other lines in which they are 7th cousins, once removed and 9th cousins, 2 times removed. But nothing closer than 7th cousins, it seems. It does seem that DNA is confirming the Mullins and Goddard descent of the Rev. John line.

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.

Even with segment length 7 cM we still get many false negatives.
This makes REV look, as expected, related to ED.
MUL matches REV (as it is meant to).

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.

The largest segments are a fairly good fit to the family tree. There are some false negatives.
GOD is not related to ED. So this shows you can get a 6 cM segment by chance.
So probably we should not look at segments below 7 cM.
You might also say MUL is not related to ED. And in general that is true. But actually MUL.1 is known related to ED.

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.

Here is the known cousins table again (for ED and REV):

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

This seems DNA-proven:

REV link to both ED branches.
REV link to MUL.