how can i know for sure with dna

+5 votes
I am new to DNA test results and have no clue what it all means with the results so I done a DNA test which I have now added to my profile from myhertage iand this it what it came back with

* Irish, Scottish and Welsh=58.4%

* English=19.1%

* Scandinavian=6.5%

* Finnish=1.0%

* Iberian=15.0%

What should I be looking for in say 3rd cousins
WikiTree profile: Steph Meredith
in The Tree House by Steph Meredith G2G6 Mach 8 (82.9k points)
All forms of DNA testing are only minor tools in the work of genealogical research. DNA testing is only one of thousands of tools available to you in completing your family history. The old fashion paper trail should be the focus of research.  DNA tests can be helpful in suggesting you are headed in the right direction. Test results always come with a percentage of probability factor and that reduces the test result to the category of secondary sourcing or even worse. Many reliable articles have been written on this subject matter over the years. The question then  becomes; are you interest in genetic research or family history research? There is no easy route to genealogical research. Far too much value and emphasis is placed on DNA testing in today's world, as a result of mass advertising campaigns.

3 Answers

+8 votes
I wouldn't worry too much about ethnicity estimates Stephanie. There is not much to be gained from trying to guess the ethnicity of 3rd cousins. They could have anything in the mix. Better to focus on analysing your matches.
by Lynda Crackett G2G6 Pilot (633k points)
+7 votes
The ethnic breakdown can be pretty inaccurate, so we call it "for entertainment only". It's the matches that help with real genealogy. As you find relatives - including somewhat distant ones - it gives confidence that your "paper trail" for that part of your tree is correct. For people with unknown biological ancestors (such as adopted people) it can help identify your close biological relatives (maybe even the parents themselves). I've also used it to identify, for example, which "William Johnson" in the US was my gt-gt grandfather's brother, adding a whole branch to that part of the tree.

With matches, it's all about the centimorgans, which is a measure of how much DNA is shared. The centimorgans can give you an idea about how closely related you are - the closer the relation, the more precise this is.
by Frank Stanley G2G6 Mach 7 (77.4k points)
So if there is a match on myheritage with 97.8cm does that means it is highly likely that the person in question is in fact a relative, have not found any on wikitree yet
You have to get down to somewhere around 15cM before you have to worry about the match possibly being false. It's just a question of how CLOSELY they're related, not WHETHER they are.

In my experience, 97.8cM is most likely to be at the 2C1R level (shorthand for 2nd cousin, once removed), but could also be an especially poor 2C match, or an especially good 3C match.

I say "level" because a number different relations can have the same average amount of DNA sharing. A 2C1R is indistinguishable, for example, from half-2C, half-1C2R, 1C3R, etc.
Yes, at 97.8 cM it's fairly likely that the person is a relative, but they could be a 3rd or even 4th cousin -- a relationship distance that many people lack genealogical data for. And you want to look carefully at the lengths of individual matching segments, as well as MyHeritage's matching protocols, to assess the chance that this is a real match and not coincidence.

Have you contacted this person to inquire about their family tree?
You also have to keep in mind that if there might be some intermarrying among relatives (like among 2nd of 3rd cousins, as is common in small communities where there are large families) that the cMs can be higher than you might otherwise expect.
Thank you all this all looks confusing to me might be worth contacting this person I found
Definitely contact!

I wouldn't worry too much about them possibly being a 4th cousin, unless there might be the intermarrying situation I described (it's called "endogamy"). That idea no doubt comes from Blaine Bettinger's famous chart, where the max numbers are apparently driven by endogamy. In my own experience, I've got 41 non-endogamy matches at the 4C level (most are 4C, some are 3C2R), and the top three are 53cM, 65cM,  and 69cM - the rest are 41cM or below. They average about 24cM. I'm on AncestryDNA, so they might be a little lower than other places (by maybe 10cM or 20cm at most). I've got all my matches above 70cM figured out, so it's not like I could have 4C matches near 100 that I haven't figured out yet - there just aren't any.

Similarly, at the 3C level I have 71 matches, and 9 of them are 90 or better (127 is my highest). So yes, it could be a 3C, but if I had to bet money, I'd bet on 2C1R. A relative that close should be someone you should be able to figure out, with a little help from your match (if they'll talk to you).

On AncestryDNA, there's a "Shared Match" feature that I use to tell which side of my tree a match is on, so you should see if MyHeritage has something like that. If the matches you BOTH have, for example, are on your mom's side, you know that they're likely related on your mom's side of your tree.
Oh, as far as WikiTree goes, I can't speak to anybody else's experience, but the closest relative I've come across here is a son of one of my jillions of 3rd cousins. I couldn't even tell you who the next closest is. If there are any 4th cousins on here, they haven't traced back to our gt-gt-gt grandparents. I have plenty of relatives out there in the real world - in America even - but here on WikiTree I'm almost like the main character in the movie "The Martian".

The mom of that 3C1R (who is my 3C) has tested, but I don't think they've even put that on here (and she's not on GEDmatch), or maybe it's just that her profile is private. So I didn't think I could use her for confirmation, but maybe the upcoming rules will clarify that.
There's a lot of variability in the size of the match as we go to more and more distant cousins. A small example:

I have a 3rd cousin once removed (3C1R) who matches me at a total of 75 cM and another who matches me at 17 cM. My full sibling matches those same two cousins at 38 and 35 cM, respectively. And we have a first cousin with the same genealogical relationship to those two cousins who matches them at 17 cM and 10 cM, respectively. So within that very small sample we see total match lengths of 10 cM to 75 cM for the same relationship distance, and we can be sure that there are some 3C1Rs who would not find any match at all.
My biggest 3C1R is 55cM, except for an endogamy case that's 64cM, so maybe this is a good example of the differences between testing companies - mine is with AncestryDNA. Looking at Blaine's data (not just his chart, which lumps all testing places together, uses means and 99th percentiles) I see that for 3C1R, AncestryDNA has a median of 33cM, but lies between 9cM and 100cM 90% of the time. For GEDmatch, it's 33cM, and between 8cM & 100cM. For FTDNA, it's 66cM, and between 30cM & 147cM.

I hear AncestryDNA decided to exclude some very common genes a few years ago, before I tested, so that's why they tend to be smaller. I'm not sure it makes sense that it would be HALF of FTDNA's, though. Probably, there aren't enough FTDNA data points for 3C1R.

Anyway, I see the same thing with my brother's results, and there are a few that I have and he doesn't, and vice versa. Sometimes the ones that are biggest for me are among the smallest for him, and vice versa.

But your first statement needs to be qualifies a little. For 3C and beyond (maybe even from 2C1R), the values start at practically zero, but the highest value you're likely to see drops. So in that sense, the variability drops.

But what you're thinking in terms of is perhaps the percentage difference vs the typical value. The parent/child values are probably within 10% of the nominal value (guessing), while for 5C it might vary plus or minus 100% from the nominal value.
+4 votes

For sure and DNA probably should not be in the same sentence at least not the DNA tests that are available to the general public and are in use on genealogy sites.  Imagine two brothers that marry two sisters and comparing the DNA of their children - while a CSI lab might work it out, the rest of us would not be able to.  Now imagine that the brothers and sisters have relations with ... hopefully you get the idea.  (If that is not bad enough add a cousin in there,)

So the answer for genealogy is - I have a paper trail that shows this relationship and I have DNA that confirms the relationship - I am pretty certain that the relationship is confirmed - but I am not 100% certain.  In today's world when we know that a woman had a child how do you know for 100% certainty that she is not a host mother, and is the biological mother.  OK - these are rare cases and not likely to be an issue - but they all make 100% certain not an option.
by Philip Smith G2G6 Pilot (307k points)
I agree with you totally Phillip. I avoid using the terminology that DNA testing confirms anything and tac in a qualifier as you have done..

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