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16cMs A genuine match?

S

sunflower

LostCousins Member
If my sister and I both share 16cMs with the same match, is there any likelihood that it could be a spurious match? I have reason to believe the family line it refers to may not be mine after all but it is picked up as a shared ancestor on Ancestry thrulines and I did know of this person through researching the tree. However is it likely to be dna match? There are several other matches on this tree with mine but they all relate to the same family.
Incidentally, when looking at the shared matches with this person, there are no others on either of our shared matches option.
 
So you are saying that all the matches which are only shared with oneself and the match are matches of less than 20cMs. That will explain why there are so many non shared matches. However, how viable is a match of 16cMs that both my sister and I share individually.
 
sunflower said:
So you are saying that all the matches which are only shared with oneself and the match are matches of less than 20cMs.
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Not necessarily but if person A is a match with person B, then regardless of how much DNA A and B share, other matches (C, D etc) will only show up as shared matches if both A and B share more than 20cM with those matches.
 
sunflower said:
However, how viable is a match of 16cMs that both my sister and I share individually.
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I'm not sure that is necessarily an easy question to answer definitively. A 16cm match is less likely to be spurious than a match of under 10cM but the connection could be further back than you expect.

I was struggling a bit to work out what you meant from your first post, but are you saying that Ancestry is showing a connection via ThruLines that you think may be wrong? Anyone shown as a 'Potential Ancestor' in ThruLines may not be an actual ancestor, as the information is simply taken from another person's Ancestry tree which may or may not be correct. Some of the Potential ancestors shown in my ThruLines are definitely wrong while others are people I've investigated but can't prove if they are ancestors or not.

Because of this, some 'Common Ancestor' matches may not be a match to you where shown, although you may be genuinely related to them elsewhere.

If I've completely missed the point and answered the wrong question, then do ask again!
 
I would have said that the fact that both you and your sister share the match it is more likely to be genuine than if only one of you had them. What you don't say is whether you have any 'Shared Matches' with this DNA cousin, and if your sister has the same ones. Your sister wouldn't be a shared match as she is below 20cm.
 
Thanks everyone for the input. I now understand the 20cm scenario and accept that reasoning.

To outline my situation the ancestors of the match my sister and I have individually has been in my tree and in others I have worked with, for a long time and as such the name was instantly familiar to me. I know this doesn't make it right necessarily but it gave me hope that I was related to the family I have researched for the last 18 years. I could not find any other matches to this family that were positive so was relieved when my first cousin finally agreed to be tested. However her test shows that we are not connected genetically but that she is to many people that I have worked with over the years. So my immediate thoughts are, that my father was not from the family we have all believed he came from.

I have his birth certificate and there is nothing untoward that I can see and I have now found an insert in the local weekly paper announcing the birth of a son to the people I knew as grandparents. This entry was within a week of his birth with nothing to say it was an adoption. So you see how important the 16cMs match was to me.

I now have to find another connection to this 16cMs match as I already know I have a family (or two now) that do not appear on my tree and are most likely my grandparents. It may be easier now to attempt to fit in all the close matches I have with a couple of families that I match dna with. It is something I have to find the solution to so I can explain to my siblings who our ancestors are and some of them are not going to be very happy about it. It is a bit of a burden I am carrying as only my cousin (not now) knows.
Research shows that our 16cMs match using parish records, relates to a brother and sister born 1777 and 1766 to the same parents so in my case my 4 x great grandparents and our match's 5 x great grandparents, so a long way back.

Pauline, writing this has made your suggestion valid so I must search for another connection with this match to eliminate from my research. As both families were based in the same village in the south of the country, it may not be too difficult. All the matches I have that I have identified with each other and a particular family are all from the north, so it is going to be very involved to see where they converge. The thrulines common ancestors connection has come from my tree which is obviously wrong now.

Thanks again.
 
Hi Sunflower,

Can you just confirm that the 1st cousin that tested is your Dad's sibling. What's going to help is understanding the shared matches between everyone. It would also be useful to have the cMs between each person.
If you have more siblings then that could be useful to test them, or your dad? Where do you have your data loaded to currently? Using more sites can help produce more matches.

Assuming your 1st cousin is on your Dad's side, then either he does not have the same father as his siblings, or it's theoretically possible that you and your sister have a DNA father who is not from your grand parents line. This is why shared matches are so important to prove/disprove these theoretical lines.
 
sunflower said:
If my sister and I both share 16cMs with the same match, is there any likelihood that it could be a spurious match? I have reason to believe the family line it refers to may not be mine after all but it is picked up as a shared ancestor on Ancestry thrulines and I did know of this person through researching the tree. However is it likely to be dna match? There are several other matches on this tree with mine but they all relate to the same family.
Incidentally, when looking at the shared matches with this person, there are no others on either of our shared matches option.
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Spurious matches come in two forms - one is a false match that results from the compromises inherent in current consumer DNA analysis; the other is a genuine match which is much further back than you might expect, and is therefore unhelpful. A 16cM segment is relatively unlikely to fall into the first category, but could quite easily fall into the second.

The fact that both you and your sister have the same match can be disregarded - all that tells you is that you and your sibling inherited the same piece of DNA from your parent. What is worth considering is whether the match is in a pile-up area, ie have Ancestry downgraded it. If so it's more likely to be spurious.

The other thing to consider is whether you have other non-DNA evidence to consider, and in this case it seems that you do.

But your priority should be to check whether documented cousins share the match - this will tell you where in your tree the match belongs. You can't do this using Ancestry's shared matches feature, you have to ask your cousins (or, better, ask the person you're match with). Also see my recent article on who should take a DNA test.
 
Peter, Other DNA testers can share their DNA results with you. This allows you to look at their test results and see their shared matches It's not triangulation but it does allow you to see common share matches.
 
Thanks for your reply Peter. Things have moved on since my last correspondence with you and the whole exercise is now going in a different direction. I am now having to start from scratch on my paternal side of the family as it is fairly obvious to me that my grandparents aren't who I thought they were. Perhaps my father was adopted, but nothing indicates that, perhaps he got swapped if he was born in the hospital but again, nothing points to hospital birth. Apart from tracing my paternal grandparents through my dna matches, I don't know what else I can do to find out why my father is different to his siblings.
If my closest dna match family were a bit more cooperative, I am sure we could come up with the answer but unfortunately, they do not seem to want to know anything about it.
The 16cMs match relates to the family I thought I had come from and is identified but the dna proves otherwise. My 1st cousin does match with a lot of other trees that I had worked with before but I am still waiting to hear if she matches with this 16cM one. If she doesn't then maybe it relates to another match (maybe on my mother's side) and not the one I had first thought. It shows that first impressions are not always the right ones.
 
Tim,

I've done that with my sister and my nephew's results but so far have not got my 1st cousin's. I will ask again for access as I am sure I would recognise any match with my tree as I have been through them all so many times. Unfortunately, she is ill at the moment so I don't like to press the point.
 
I have now had access to my cousin's matches and she does not have the 16cMs match. I now conclude that there is no hope that I come from the family I believed I did. I have 5 siblings and 3 of us have tested and match with another family altogether on my paternal side. At first I was going on the premise that my paternal grandparents, as I knew them, were not the parents of my father. I am now thinking quite strongly that may be my father is not that, but 3 out of 6 seems a bit high for an occasional fling on my mother's part. I don't want to believe it but the science is tells me otherwise so I must investigate it. I can't ignore it now. My eldest brother is very much like our father, even sounds like him, so I can ignore him and see if the other two will test for a complete picture.

I have just re-established contact with a member of this other family so I might now be able to sort it out especially as they have agreed to taking a test. We could end up with a whole load of half siblings.

Thanks for your suggestions and for helping to sort this out.
 
peter said:
That's what I was suggesting.
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Oh, I read what you said as ask the shared matches if they match that person. What I was saying was that DNA tests can be shared, and then you can look at all their matches yourself.

Once the other person has shared their DNA test with you, you can select it using the "View Another Test" Button.
 
Tim, I have done that with a few and have access to 4 dna test matches which I use constantly. The consequence of which has allowed me to build up a database of matches and using other sites even down to chromosomes. If as I suspect, the new information regarding my new family is true, then I have a lot of data on a tree I have already built up. By expanding these laterally, I can probably tie in a lot of the matches that mean nothing to me at this stage. The names in my original researched tree are engrained in my mind having built them up over the last 18 years. The new family are not so familiar.

Thanks again and Happy New Year to all Lost Cousin participants.
 
Hi Sunflower, so far there are 3 of you who have the same genetic father. Yes it makes sense to test all your other siblings to see if you are full or half siblings. If your eldest brother is like your father then for me this is the person I would test first. If you're a full match with him then your family father is your genetic father.

How many cMs do you share with your first cousin?
 
Hi Tim, My father and my cousin's mother were brother and sister (so we always believed) but I do not share any dna with my first cousin. so this means either they were not brother and sister or my father is not my sister's, younger brother's or my genetic father, which is looking most likely.
 
Hi Kirsten,

She could be but she matches dna with people that I have worked with for many years on 'our' family tree but I and my siblings don't. So everything in her dna points to the family we believed we were part of.

My elder brother has now taken a test and we wait for the results. I have also persuaded someone from the family I appear to be genetically part of, to do a test as well. They are the parent of one of my matches, so their total cMs will indicate if they are a nephew/ niece, a half nephew/niece or 1st cousin/1 x removed. I should have the answer on the closeness to this family fairly soon.
 
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