Can a half 3rd cousin once removed be a full 3rd cousin once removed?

[KD146]

I have a DNA match on Ancestry with a 3rd cousin once removed.  However, Ancestry says we are matched through my 2nd great grandfather only, not my 2nd great grandmother.

Her 2nd great grandfather (my great granduncle) is the only one among six siblings who I found no baptism for, though he seems to have been born fourth of the six siblings.  His 1877 marriage cert states both my 2nd great grandparents as his parents.

My question is, could he be a full sibling to the others, and we have simply missed my 2nd great grandmother's DNA, or is the DNA telling us that he was definitely a 'brother from another mother?'  Many thanks.

EDIT:  We share 51cM over 3 segments.

[Flemming]

Is this more to do with other people's trees having a different 2x great grandmother, or perhaps the name and/or birth dates/places differing between trees so Ancestry assumes they're different people?

I've got a few like this where Ancestry only gives one common ancestor, not a couple, and it's usually because the one that's missing has inconsistent information across different trees.

[KD146]

No, we both have the same name, and dates of birth and death for my 2nd great grandmother.  It's a puzzle.

[Flemming]

If you open your match's page and click on the 2x great grandfather box under Common Ancestors, do you then get a page that shows you the 2x gg at the top and the descendants of you and the match below this? On your match's descendants, do you see any green flags that say 'Evaluate'? If so, you can click on these and a panel should appear on the right which shows the various trees that Ancestry has taken the information from. Some of these might have different information to you/your match and Ancestry might be using theirs not yours.

I've got about 20 matches where I've made a manual connection and our mutual trees are the same but Ancestry resolutely will not find the common ancestors. I've also got a few where my tree differs to the match's and Ancestry follows their tree, not mine (no idea what the match sees because they don't reply).

[KD146]

Well, the puzzle resolved itself, because I opened my match page like you said, only to find that my 2nd great grandmother has miraculously appeared as a common ancestor.  So we are descended from both!  I didn't change anything, and my match doesn't seem to have changed anything, but something must have changed.  Anyway, it does mean that everything is straightforward now.  Many thanks!

[medpat]

I use DNA Painter

https://dnapainter.com/tools/sharedcmv4


results for 51cMs - note 17% possibility

30%   Half 3C 3C1R Half 2C2R 2C3R24%5C3R † 6C2R † 7C1R † 8C † 6C 6C1R 5C 4C1R 5C1R 7C Half 3C2R 4C2R 5C2R 3C3R 4C3R

21%    4C Half 3C1R 3C2R

17%    3C Half 2C1R 2C2R Half 1C3R

7%      Half 2C 2C1R Half 1C2R 1C3R

~ 0%  **2C 1C2R

[LizzieL]

I have number like that where Ancestry tells me it is a half relationship and I know very well it is a full relationship. The closest was my first cousin's daughter, who Ancestry said was my half 1st cousin once removed, saying the relationship was only from my grandmother (her great grandmother). Somehow this has now been rectified and we now show up as a full relationship, despite the fact she still has my grandfather's birth year wrong. She hasn't logged in for over a year so it isn't a change she has made.

[Pheno]

I think both cases relate to changes other people have made in their trees.  Ancestry use all the trees they can in putting the common ancestors together and the majority tends to dominate.  Even if the ones you know about have got it right, if there are many others with something different which leads Ancestry down a different path then that's what they go with - they don't actually check the relationship out.

You can check which trees they are using by using the Evaluate button as Flemming says.

The only way I managed to correct an 'incorrect' half relationship was to contact all the people with trees that Ancestry was using to create the relationship and point out the error of their ways and ask them to amend the descendancy in their trees.  Enough did having had the correct relationship pointed out, to make a difference to the match and thrulines.

Pheno