Author Topic: Surprising but probably not that unusual DNA result  (Read 667 times)

Offline Pinetree

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Surprising but probably not that unusual DNA result
« on: Tuesday 19 May 20 20:40 BST (UK) »
I have been spending a bit of time looking into DNA matches and their trees.  A couple of "triangulated" links are particularly interesting because although the same names come up in all of our trees according to my research from the records the link is by marriage only.  So where has the shared DNA come from?  :-\

I imagine this happens quite a lot.

Pinetree



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Offline Craclyn

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Re: Surprising but probably not that unusual DNA result
« Reply #1 on: Wednesday 20 May 20 22:15 BST (UK) »
Develop the trees further back and see what you find.
Crackett, Cracket, Webb, Turner, Henderson, Murray, Carr, Stavers, Thornton, Oliver, Davis, Hall, Anderson, Atknin, Austin, Bainbridge, Beach, Bullman, Charlton, Chator, Corbett, Corsall, Coxon, Davis, Dinnin, Dow, Farside, Fitton, Garden, Geddes, Gowans, Harmsworth, Hedderweek, Heron, Hedley, Hunter, Ironside, Jameson, Johnson, Laidler, Leck, Mason, Miller, Milne, Nesbitt, Newton, Parkinson, Piery, Prudow, Reay, Reed, Read, Reid, Robinson, Ruddiman, Smith, Tait, Thompson, Watson, Wilson, Youn

Offline Eric Hatfield

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Re: Surprising but probably not that unusual DNA result
« Reply #2 on: Saturday 23 May 20 00:04 BST (UK) »
You didn't say how large the matches are. If they are relatively small, then they can be due to those segments being shared by a large population. For example, in a localised area or a clan, most people may be descended from roughly the same group of common ancestors, a long, long way back.

That is sometimes called Identical by State (IBS) and this excellent site describes it this way:

"identical by state includes two categories that are mutually exclusive; Identical by Chance and Identical by Population. .....

Identical by Population means there IS a common ancestor, and you did receive your DNA from that ancestor, but you may not be able to figure out who it was because itís too far back in time and many people from that same population base share that DNA segment."


Offline Pinetree

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Re: Surprising but probably not that unusual DNA result
« Reply #3 on: Monday 25 May 20 12:20 BST (UK) »
Thank you both for your replies.

I am absolutely no expert, in fact a complete novice, when it comes to DNA so I am sure you are right that there may be common ancestors I have not been able to identify further back.  Although the shared DNA 67.6 cM is similar to the amount shared with a known relative (from another branch of the family) who is not that distance and the largest shared segment is bigger at 25.5 cM.  Only 5 shared segments as opposed to 6 shared with the known relative though.

Pinetree

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Offline squawki11

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Re: Surprising but probably not that unusual DNA result
« Reply #4 on: Sunday 31 May 20 16:20 BST (UK) »
You don't say which company produced the matches. Each has a slightly different way of measuring the size of a match. FTDNA can include many small segments, whereas Ancestry attempts to phase the data and trim the size of the match. 23andme includes X in the overall total. If your shared (Ancestry?) matches are all c.60+cM, you might well be able to find their relationship to yourself by developing your tree widely and deeply, including siblings and as far back as you can go. Clustering using Collins Leeds method can produce good representation but tree info is still vital. The overall size of the match is more important than the number of segments imo.