GEDMATCH and MRCA

Question

Does anyone know how accurate the MRCA calculations at GEDMATCH are?

On paper for about 20 years I have tried to find the parents of my ancestor Susanna A. Mowery. Over ten years ago, Maurer researcher Robert S. Mowery and I put our heads together (his work being much more voluminous than mine) and came up with the theory that she was a daughter of Valentine and Susanna Mowery.

His work on this branch is available here:

http://www.genealogy.com/ftm/m/o/w/Robert-S-Mowery/GENE15-0001.html

Fast forward to 2017. Even though I have been DNA tested for years, I very recently in the last two months have had two separate matches to two different descendants of Leonard Mourer (and wife Elizabeth Sheetz), the brother of Valentine Mowery. GEDMATCH has our MRCA estimate at 4.4. The number of Leonard's children is not set in stone, but is not as open as Valentine's family for which there is very little documentation.

Robert S. Mowery's work on that branch is discussed here:

http://www.genealogy.com/ftm/m/o/w/Robert-S-Mowery/GENE11-0001.html

Not enough descendants have tested to be able to place Susanna properly -- I only have the two matches who descend from Leonard, but the results are gratifying after waiting so long for any real link. I am not putting anything on Wikitree until there is more data to draw on

So for discussion's sake, is that generation estimate accurate enough that she would be a daughter of Valentine versus Leonard, or is there a possibility that she could have been Leonard's daughter?

Dina

Answer 1

DNA can't tell you how you are related to another person. These are just estimates of the genetic distance between two people. You need to use genealogical evidence to figure out how the two people are related.

Comments

My question is about that estimate of the genealogical distance. I am curious about peoples' experiences with the number of generations and the accuracy that shows in their own work.

Robert S. Mowery and I came up with a theory using the evidence that we had that Susanna was Valentine and Susanna's daughter. That has not changed. What has happened is that I have shared DNA with two descendants of Leonard Mourer and Elizabeth Sheetz, one through son Philip and one through daughter Sophia and GEDmatch shows our MRCA estimate as 4.4.

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Dina, my experience has been that Gedmatch is pretty close on MRCA estimates.  When I have a 4.4, it's usually 5.  Depends on the size of the segment.  Are you sharing a common segment with both descendants, or are you sharing one segment with one descendant and one with the other?  Also, what is the size of the segment?

I found your question more interesting than average, as I have a Maurer brick wall in my ancestry.  I never thought about a possible spelling of Mowery.  The ones I've located thus far are Mower, Mowder, Mouder, Maurer, Mourer, Moder, Mauerer, Mauder.  Mine were in Pennsylvania and supposedly from Scotland . . .

Answer 2

I find that the gedmatch estimates are reasonable, but you have to allow for the fact that may be a generation (or more) removed on one side of the match which has to be taken into account. A result such as your 4.4 usually indicates a remove in the relationship. Also that there will always be some cases where the relationship calculation may have been skewed by endogamy or for other reasons. I have not had time to look at the details of your specific case.

Comments

I've seen +2 and -1 for the genealogical record compared to the DNA estimate (so, gedmatch says 3 and it's actually 5, or gedmatch says 4 and it's really 3). That's on a fairly small sample (less than ten on gedmatch) but similar to the results I've had with Ancestry and FTDNA.

Answer 3

You can put limits on how close or far away a connection is as shown in this table giving cM ranges for various relationships:

http://isogg.org/wiki/Autosomal_DNA_statistics#mediaviewer/File:Shared_cM_Project_v2_updated.png

It gets tricky though if you have two paths to a person that are similar number of generations away.