(by identifying and/or eliminating ancestral lines which are “unlikely” or “highly unlikely” to contain the common ancestor)
If you and your match have extensive family
trees and you have been lucky enough to trace every one of your ancestral lines back 10
generations, then it should be a simple matter of comparing your list of
ancestors and picking out the one you have in common.
However most people, especially when it
comes to researching Irish ancestry, can only go back to the early 1800’s or
the mid-1700’s at the earliest, and then not in every ancestral line. In that
situation, you will be looking for a common ancestor who does not currently
appear in your tree. It is important in these circumstances to narrow down the
number of ancestral pathways down which the shared DNA could have passed. This
helps focus your research and eliminates dead ends and ancestral pathways which
are not contenders.
Several techniques allow us to identify
ancestral lines that are either “unlikely” or “highly unlikely” to be those of
the common ancestor. By eliminating non-contenders, we reduce the number of
possible candidates for common ancestor, and reduce the number of ancestral
lines down which the shared DNA could have passed. This process of elimination
increases our chances of identifying the common ancestor, or, at the very
least, the ancestral line on which he sits.
We will deal with each of these techniques
in turn:
3.1 Can you tell if the match is on your maternal
or paternal side?
3.2 Do you match each other on the X-chromosome?
3.3 What is the likely ethnicity or
nationality of your common ancestor?
3.4 How to do Phasing and use it to
identify which grandparental line contains the Common Ancestor.
3.5 Other factors?
3.5 Other factors?
I liken this process to playing a game of
cards. In the example below, imagine that the suggested relationship for you and your match is 2nd cousins. This predicts that you share a common great grandparent - but this could be one of 8 people in your tree and one of another 8 people in your match's tree. Using the above steps, we can whittle down the list of possible candidates to just one single person in your tree - your mother's father's mother (ahnentafel number 13).
You start off
with a full deck of ancestors, but by a process of elimination you can (for
example) …
|
|
get rid of all
your paternal ancestors
(step 3.1) |
|
then all your
“non-X” ancestral lines
(step 3.2) |
|
then lines of
improbable ethnicity/nationality
(step 3.3) |
|
and then one of your
grandparental lines
(step 3.4) |
|
So this step is very important for getting
rid of ancestors and ancestral lines that should not be given further
consideration. This becomes even more important when the relationship with your
match is quite distant (e.g. 4th or 5th cousin) and the
number of possible candidates is quite high.
Now let’s look at each of these techniques
in closer detail and explain a little of the science behind each one, followed
by some instructions on how to do them in practice.
Thank you so much, this has been so helpful!
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