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2nd Cousin DNA Match Accuracy

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2nd Cousin DNA Match Accuracy

Postby Lemki927 » Sat Jul 28, 2018 5:35 am

Hi Folks

Wondering if someone can help answer a question. My brother recently did the Ancestry DNA test - in the reference of online relatives, they matched him with a 2nd cousin, who we know. This woman is a cousin on our maternal grandfather’s side - our mother’s first cousin. Ancestry says we are 1st or 2nd cousins, confidence extremely high. So all checks out.

My question is: there was a story floating around years ago that our maternal grandfather was not in fact our grandfather, and the man in question was his first cousin on his mother’s side. Would this Ancestry linkup then invalidate that idea? If that story were true, this woman would technically be our 3rd cousin.

As the DNA is close between the two men who could be our grandfathers, is this test accurate enough to rule out that possibility? I will do the test also in the coming months and see what results come from it.

Any thoughts would be appreciated

Lemki
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Re: 2nd Cousin DNA Match Accuracy

Postby JaneyH » Sat Jul 28, 2018 8:20 am

Like other sites, Ancestry is only suggesting a relationship based on the amount of shared cM. The ‘DNA shared cM project’ will tell you the range of potential relationships of a match and their likelihood. Their tool is here: https://dnapainter.com/tools/sharedcmv4

There’s a very helpful Facebook group where you may find it useful to post your query - search for ‘DNA help for genealogy (UK)’ and you should find it.




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Re: 2nd Cousin DNA Match Accuracy

Postby DianaCanada » Sat Jul 28, 2018 9:29 am

If, hypothetically, your grandfather is John Smith, son of George Smith and Sarah Jones and the possible grandfather is Bob Jones son of Harry Jones and Ann Thomas, you should match other relatives from either the Smith side OR the Thomas side as well as the Jones side. With a fairly close relationship such as this, you should see a pattern emerging by carefully going through your 4-6th cousins.
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Re: 2nd Cousin DNA Match Accuracy

Postby Lemki927 » Sat Jul 28, 2018 12:31 pm

Thanks for the replies

Our second cousin registers at 439cm and 26 connections. We also found another second cousin on that side who registers at 366cm and 22 connections.

I guess this would make them very healthy 2nd cousins? We did find a few third cousins who we know, who have much lower numbers. The numbers for the second cousins are a bit high for the charts listed - perhaps Ancestry has a different scale...

Any thoughts?
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Re: 2nd Cousin DNA Match Accuracy

Postby DianaCanada » Sat Jul 28, 2018 3:03 pm

Am not sure I am answering your question but cousin ranges can be quite wide even for siblings. One match on Ancestry is a 3rd cousin to my brother with 113 cM shared but a 4-6th cousin for me, with only 35cM shared. In some cases my daughter and I are related to someone in the 4th-6th range but my brother is not even registering as so little is shared.
I think in many cases the numbers can be quite disparate (which is why many people suggest as many sibs as possible test) so a family tree to help with the connections is so helpful. Of course, most people on Anc don't bother....it can be frustrating!
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Re: 2nd Cousin DNA Match Accuracy

Postby Mick Loney » Sat Jul 28, 2018 3:46 pm

DianaCanada wrote:I think in many cases the numbers can be quite disparate (which is why many people suggest as many sibs as possible test) so a family tree to help with the connections is so helpful. Of course, most people on Anc don't bother....it can be frustrating!


Diane,
Don’t get me started! :D Too many people seem to think having a DNA test will solve all their genealogy problems, and don’t need a tree!

It is so frustrating to find a potential 3-4 cousin, and then discover that there’s not a tree to help identify the common Ancestor, and 60% of my Ancestry matches don’t have a tree! Ancestry don’t help, as they don’t give any details on which chromosome the matches occur. You need a third-party site like Gedmatch.com to progress the matches further.

BTW, I have one potential ‘strong’ 3-4 cousin match, with a tree, yet we cannot find any common ancestral links at all - go figure! (Possibly a non-paternal event has occured somewhere :D )

Mike
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