DNA connections through 5th - 8th cousin matches

[EllaLees]

Hope this makes sense. My mum & I have a 5th to 8th cousin DNA match (No other shared matches with him), who shares the same 4th great grandparents to my Grandfather's 1st wife ( I’m descended from my Grandfather's 2nd wife, and have DNA matches to confirm). In my distant cousin's family tree, he has mapped from himself to said 1st wife which has linked us as a possible DNA match through that link, obviously possible there are mistakes but he is fairly confident from researching with other distant cousins that his line is correct. However, 1st wife is not my grandmother, if his tree is correct how could I be DNA linked to the 1st wife if I'm descended from the 2nd wife?  Are there any suggestions as to how I could be DNA-connected? Is it possible my Grandfather & 1st wife had a child who would be a half-sibling to my mum, could that be how the DNA is linked? Or is this just a coincidence he's linked to the 1st wife and we must be DNA matched through a different line? I can’t get my head around it. Thanks Ella

[rsel]

Hi Ella,
  There are a couple of options to consider :

1) I assume you are saying that the connection is being reported via thruelines/common ancestors ? If so then these are based on peoples trees, rather than DNA directly.  So its possible there is a set of incorrect trees somewhere assigning both yours and your matches relative to the 1st wife, which is then screwing up the relationships. I have a number of 'common ancestors' which have been suggested and when i have looked at the matches tree they are totally different (i.e. tree shows A descended from B, who descends from C. but the suggestion shows A, B, and E as the path).

2) Have you made a mistake in your understanding that the 2nd wife is you relative rather than the first (or even the other way round) ? Not knowing the circumstances of change in spouse, is there anyway both of you could come from the same wife.  Whilst you mention having DNA proof to the 2nd wife, could others have also problem with having the incorrect one.   Based on what you have said, i think this is an unlikely option, but when you rule out the possible options, you are often left with the improbable ones :-)

Richard

[Biggles50]

Assume any Thruline is totally in error, many simply do not make sense i.e. you can find say John Smith and when you look at the trees it shows his father as Tom Smith.

You go back to the Thruline where it shows his father as Bill Smith, and so it goes.

As your are looking so far back the probability of detecting a DNA connection correctly is down at 15% and when you get to 7C it is less than 5%.

With Pedigree Collapse you can have an abnormally high cM.

You can even find that as is the case in my Wife’s matches she has two on the same line one 38cM and the other 30cM.  The MRCA with them and my Wife is at her 4xGGP’s yet to each other their MRCA is their 2xGGP’s.

What makes this odd is that the Grandson of her Maternal Cousin is a match to one of them but not to the other, such is the way DNA is inherited.

[LizzieL]

Assume any Thruline is totally in error, many simply do not make sense

I completely agree
Thrulines are based on other people's trees - whether they're 100% correct or a total load of rubbish.

I have two half fourth cousins once removed. They are first cousins to each other. Our MRCA is my 3 x great grandfather (John), but they are descended from his first wife Harriet and I am descended from his second wife Sarah. I have a thrulines connection to one of these cousins as she has identified the correct Sarah as my ancestor in her tree. But I have no thrulines connection to the other cousin as she has picked a random Sarah with the wrong surname who lived three counties away and happened to marry a John with the same surname as our common ancestor John. Not only did this other cousin ignore the maiden name of mother (later children of 2nd marriage born after 1837), but ignored the fact that the marriage between the wrong John and the random Sarah was in 1820, our John married their Harriet in 1821 and my (correct) Sarah in 1828 - so he committed bigamy twice!

[lisalisa]

It could well be that you match the 5th to 8th cousin on a different line as you suggest, or that you match the line of the grandfather's first wife on a different line - quite possible if everyone lives in the same area.

Another avenue might be to do trees for both the 1st and 2nd wife and see if they are connected anywhere.  Sometimes it may be necessary to go quite a long way back.