Some folks DNA related to me but not my cousin who also took a test

[Biggles50]

Through Roots Chat I met a 3C in 2012.

We eMailed each other fairly regularly and kept in touch to help each other out with the family line that was common to us both.

Our Common Ancestor was my Great Great Grandmother, who was a bit of a lass with her favours so much so she had at least three children out of wedlock to different Fathers (her Sister had two).

I am a DNA match to one of her Sister’s descendants and to others via a MRCA beyond my GGGM.

I met my 3C for the first time earlier this year before she passed away and we brought each other up to date on family research.  Alas even though she had taken a DNA test I was not showing as a match to her, nor was she seeing any of my Shared DNA matches in our GGGM’s line nor any DNA Matches in the line of the man our GGGM married.

Such is the spanners DNA can through up, she has all the paperwork but DNA does not show any matches in our Common Ancestor’s line.

Again this is another image I have posted before and it shows how one can not inherit DNA from a specific xGrandparent.  The image is only valid for the person to whom it is applicable, we each will have our own version.

[Alan of Kaslo]

Thanks again for the comments! Really enlightening.

I thought I'd post a visualization of what I'm going through here.

The first panel is the distant cousin i'm related to on ancestry. His great great grandfather is the potential father of my grandmother. All clues point to it but the distant cousin does not show as DNA-related to my 2nd cousin who also took a test.

[Alan of Kaslo]

Here's me for comparison:


What ancestry says about me and the distant cousin:

You and
4th – 6th Cousin | Parent 1's side
Shared DNA: 39 cM across 2 segments
Unweighted shared DNA: 44 cM
Longest segment: 27 cM

In your experience ... is it possible that a person could have this type of DNA-match and share the same great-great grandfather? Now that I look at again, it seems that this person would be my great grandfather and this distant cousins great-great grandfather (one additional generation).

I had assumed the DNA cm's would be higher... but I have been mistaken about a lot of DNA so far.

Thanks so much for any help.

[Alan of Kaslo]

Last piece of the puzzle.

My 2nd cousin's tree for comparison. It seems like he should show up as a match to the relative of "potential father". It's not too many gens back... but I don't know much about this DNA business. That's why I posted here and see what you kind folks think of the likelihood.

[Biggles50]

Can I park your actual Cousins for now.

What I suggest is you build a new tree based on the DNA match and look at the Shared Matches between you, and try to build them into the tree.

When you have a few DNA matches in the tree export it to a Gedcom file.

Whilst you are building the tree take time out to learn about DNA Painter’s WATO tool.  For what I suggest it that you upload the Gedcom file and complete the WATO analysis.

It may help in determining where the link is likely to have occurred.

[Glen in Tinsel Kni]

If you check the dropdown list of relationships/probabilities by clicking the shared cM on Ancestry there will be something like 25-30 possible relationships ranked from most to least likely.
The majority of them will be variants of full/half 2nd and 3rd cousins, it would be perfectly normal for the top two most likely groups to have almost the same probability as each other.
Those in the 4th-6th cousin range will be far fewer in number and likely to have a much lower probability percentage.

[Alan of Kaslo]

Thanks for the help. I'll keep looking into things and follow some advice from here.

Cheers.

[Alan of Kaslo]

Small update. I spent a few days poking around in thru-lines looking carefully at various connections. I started noticing things I hadn't seen before ... basically everything we discussed in this thread. I saw many examples of the randomness of DNA being passed down.

I saw people 4 generations back with almost double the cm's of someone 3 gens back. I saw multiple people all related to the same grandparent and the same number of gens from that person with completely varying amounts of DNA and some were connected to this cousin I keep speaking of and others were not.

I found a scenario where a related person was 3 gens away from a set of grandparents ...he was related to a sibling of my g grandmother (same setup as what I have been trying to compare to) and he had 38cm DNA whereas the connection I was comparing to had 40cm.

None of this really gets me any closer to knowing if this individual was my great grandfather ...but I now know it is a possibility. Rather than disprove the possibility in fact looking at the DNA does the opposite. He could conceivably be my g grandfather but now I need more clues to prove. I'll keep at it.

I'll have to keep looking into things. Thanks for sending me on the right path!

[Jane Stewart]

Your Ancestry test did not analyse your whole DNA, just about 7% so you should see how variances can happen.

Note that Ancestry does not test your whole DNA, but it is comparing the same area of DNA that is in fact less than one percent of your DNA (not 7) between you and another person.  All humans are over 99% identical - this part is ignored completely!
Eg. you and your child will share "50% DNA" (of that 1%).

By the way the son of your father's sister's child is your first cousin once removed (1C1R), not second cousin. 
See the possible variations here
https://dnapainter.com/tools/sharedcmv4