DNA: Matches in Common, part 1

One of my father's closer relations in the genetic pool at 23andMe also matches his paternal first cousin, once removed.  Here is what the graph looks like:

23andMe
J. H. compared to D. W. and Jody's Dad

J. H. matches D. W. on the same area of Chromosome 2 that he also shares with my father.  D. W. is in the generation older than my father and shares a slightly larger segment with J. H.  The relation is still distant, beyond third cousins.  The chances of inheriting the same intact segment is random, but here it is.

This match in common was surprising because it seems that J. H. shares an ancestral line on my father's mother's side as well.  If you travel back to Massachusetts in the 1630s, you will find the couple John Strong and Abigail Ford.  My preliminary research indicates that J. H. is descended through their son Jedediah while my paternal grandmother was descended from another son, Jerijah.  400 years later, it is not likely (dare we say improbable?) that such a large segment of DNA would still be intact from John Strong or Abigail Ford.

The new results demonstrate that there are more recent common ancestors, not in my father's mother's tree, but in my father's paternal grandmother's tree.  See how adding a cousin for comparison helps?  You still need to research records as we have been all these years to figure out where J. H.'s tree merges with mine.  It's like getting the answer first and figuring out the arithmetic later.

DNA: Comparing the Closest Matches

Remember my 5% mystery match from a year ago at 23andMe?  From the new parental sorting feature, I discovered that he is a match through my mother.  This person has not responded to my requests to communicate.

To put into perspective how close a relation this mystery 5% man is to me, look at my closest genetic relations in the database.

23andMe
The P stands for Paternal Match and the M stands for Maternal Match.

D. W. is my known first cousin, twice removed.  The displayed relation of 2nd cousin is a prediction.  Second cousins (children of first cousins) should share about 3.125% DNA.  D. W. is my grandfather's first cousin, so the same spacing exists between us as second cousins.  [For DNA purposes, D. W. is better than a second cousin because he represents the DNA from two generations ago at my grandfather's generation.]

This mystery 5% cousin shares slightly more DNA with me than D. W. does!  That is how close a relation he is to my mother's family and why I really wish he would come forward.

DNA Testing: Results for Grandfather's First Cousin

The DNA results are in at 23andMe for my grandfather's maternal first cousin!

First cousins share around 12.5% identical DNA.  My grandfather is not available to test, but we do have the next generation:  his son.  The expected amount of shared DNA is reduced in half, or about 6.25%.    The actual shared DNA between these first cousins, once removed, is 6.71%.  As the next generation, I could expect to share about 3.125% with a first cousin twice removed.  Again, the amount of shared DNA is slightly more at 4.44%.  [Extrapolate on these numbers for a few more generations and you can envision how some of your ancestors' DNA becomes undetectable.]

Relative Finder at 23andMe
My father's top three matches.

23andMe
DNA comparison between First Cousins, once removed.

23andMe
DNA comparison of First Cousins, twice removed.
The blue areas represent some of the DNA that I carry of my great grandmother, Laura Winterton.
This is truly amazing to see.  Although she is gone, I am able to see her in me by comparing myself to her nephew.

Last year, after testing my father's maternal third cousin, we discovered that he also matches my mother, though we do not know how.  In this same spirit, my father's paternal first cousin matches my mother's brother.  We do not know how.

23andMe
This testing creates new questions to be answered.
This paternal cousin is somehow related to my maternal uncle!!!

So what is the point of testing these different family members?  To narrow down the other matches to specific branches of the tree.  When a distant genetic relation matches both my father and his cousin, the search for the most recent common ancestor is narrowed to my father's paternal grandmother's tree.  Many of these lines have old roots in Monmouth County, New Jersey.

In upcoming posts we will examine some of my father's matches who also (surprise!) match this first cousin.