CASH
DNA testing - inside the Cashel tree.
For background see
DNA testing for the Blennerhassett problem.
As part of the testing, we proved many lines inside the known Cashel tree.
Groups
We compare individuals from the
groups defined here.
This page will compare:
First, we lay out the
known relationship (from the family tree) of the people inside CASH.
Then we can compare the DNA results to their
known cousin relationship.
Here are the known cousin relationships.
All the people here descend from George Cashel (born 1807).
- CASH is divided into two groups, representing two different children of
George Cashel:
- CASH 3 to CASH 1 (as laid out here, not numerically)
are the descendants of Blennerhassett Cashel (my branch).
- CASH 2 to CASH 14 (as laid out here, not numerically)
are the descendants of Edward Francis Cashel (the Alaska branch).
We start the DNA analysis by considering total segment matches, using minimum segment size = 9 cM.
9 cM is generally considered significant.
We compare these known relations within the Cashel family.
Note that we get false negatives:
- This shows that we can get false negatives.
This far back, you can be related but not have it show in your DNA.
-
False negatives will happen this far back.
False positives will not really happen. Any strong match means you are related.
Though it does not mean you are related through the line you think you are.
The DNA positives here make sense and match the family tree.
It clearly show the two groups:
- CASH 3 to CASH 1 are the descendants of Blennerhassett Cashel (my branch).
- CASH 2 to CASH 14 are the descendants of Edward Francis Cashel (the Alaska branch).
-
The two groups have strong cross-group matches.
My branch is related to the Alaska branch.
Much of the Cashel tree is now DNA-proved:
- Between these matches on Gedmatch,
and other matches on Ancestry,
much of the Cashel tree is now DNA-proved.
-
Search for DNA proven lines in my tree
(see the Cashel section).
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 false negatives in
the CASH branch (common ancestor born 1807).
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.
- CASH.14 shows how hard it might be to get Blennerhassett DNA matches:
- CASH.3 to CASH.1 (as laid out here)
are the descendants of
Blennerhassett Cashel.
- We know that CASH.14 is related to them.
CASH.14 is a strong DNA match of its own group,
and that group has many strong DNA matches with the Blennerhassett Cashel group.
-
The common ancestor is
George Cashel (born 1807).
- But, even though we know they are related,
CASH.14 has no match greater than 13 cM with the Blennerhassett Cashel group,
and
no match at all with most of them.
- The postulated Blennerhassett common ancestor is 2 generations higher up.
Does this make DNA impossible to prove it?
- Not quite.
We are able to get DNA from people 3 and 4 generations higher up than CASH.14.
So it is not that impossible to get a match with Blennerhassett for those people.
But CASH.14 shows how quickly it becomes hard/impossible to detect even close relations in the DNA.
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:
The Gedmatch estimated MRCAs
are a fairly good fit to the actual cousins on the family tree.
There are some false negatives.
