A Question about Triangulation

Question

Independently 2 of my daughters took autosomal tests and gave me their results to upload into Wiki. They are 1/2 sisters. I was estranged from my father's family during my parents divorce when I was a little girl. Lo and behold perhaps a 1st cousin but at least a 2nd cousin is on wikitree. It's okay to triangulate between him and my 2 girls for results on my father right? or no?

would it be ok for me to triangulate with them to get results on branches that don't have any descendants on wiki at all? It'd be great if I didn't have to hunt down unfamiliar cousins, however remote they may be, on ftDNA when I have ready "resources" (I'm not sure how they'd feel about being labeled "resource" lol).

This is one of those times a lack of good communication skills can be awkward...

Answer 1

Hi, Amanda! For your parents and their ancestors, no; you don't use your daughters' results at all. Your daughters each have a subset of your DNA; of the half of the DNA they got from you, it can only have come from you. In fact, a common test to see if a reported match is false is to see if the parent is also a match. In other words--discounting the DNA their fathers' gave to them, of course--if your daughters show a cousin match on your side of the family that you don't show, then classify that as a false match.

Those false matches pop up more than some people realize. They almost always involve only small segments, and it happens in part due to two main reasons.

Our common microarray tests look at only a tiny fraction of our DNA, about 0.02%. And not only do different vendors use different tests, but even the same vendor will typically use a different microarray chip for each of its major versions of tests. The greatest disparity I've seen is only a little over 21% of the same markers being tested.

In order to make 0.02% of the DNA and a near-80% difference in markers work, there's a lot of stuff going on behind the scenes that we almost never see. A lot of genotyping, assumptions, imputations and, well, just some plain guesswork.

We also have to keep mind that segment start and stop positions are never precisely as reported. They really can't be with our current tests. That's another of triangulations several failings. Since only 0.02% of the markers, or SNPs, are tested, segment start/stop can only be reported based on the markers that were specifically examined by whatever test and version of test was taken.

This doesn't make much difference to us when we're dealing with, say, segments of 25cM or larger. But the errors creep up going lower than that. As an example, just within the past couple of days and as a result of Family Tree DNA making big changes to their website and matching algorithms, fellow WikiTreer Dr. Ann Turner checked the accuracy of reported segments using the results she has from both her son and her husband. Since all three were tested, we'd call that traditional trio phasing: the son could have received no DNA that didn't come from either Ann or her husband.

She analyzed a total of 5,652 segments of her son's being reported as matching someone else. She used segment sizes ranging from 7cM to 25cM. At 25cM and larger there were 173 segments, and they all correspondingly matched either the mother or the father. Good to go! It wasn't a smooth curve, but with every cM decrease below that, there were at least two false segments reported. In all, at 25cM and lower, down to 7cM, she found 1,023 reported segments that were false, or about 18% of the total.

Your daughters' results will be very informative about the paternal sides of the family. But you should use only your own results for comparisons with your relatives. If your mother was tested, then we'd want to use her results instead of yours for her side of the family.

Comments

@Amanda: Seeing how many descendants Mary Eliza (Lee) Groover had, and seeing that there are some lines in other branches of your family where you don't know about the existence of children, I would think that you have some more cousins out there somewhere whose data could contribute to your quest. Additional cousins might turn up if you take auDNA tests at additional companies, or maybe more new test-takers will appear (like Carolyn did) if you simply wait.

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@Ellen

Patience? must grin...

okay, so wait and a "cousin" might appear at some point. I could do that. and check back occasionally to see what the net has pulled in from the sea...

When will I know the information is qualified for a DNA verification? What am I looking for that Wiki can use? or gedmatch from the list, although they caution us to not show information which to me says it's useless here, right? or is there a method I can use a segment to segment comparison for Wikitree purposes?

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Patience is rewarded sometimes.

Several years after joining 23andMe, I was pleasantly surprised by the arrival of several new 23andMe members with strong DNA matches to me who are 3rd cousins (from two different families) previously not known to me. It was not hard to work out how they were related, because I knew about their great-grandparents.

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Amanda, if you have a match with a third cousin or closer, you might want to try using the DNA confirmation citation maker here: DNAconf (wikitree.com)  It will help you figure out which relationships can be marked 'confirmed with DNA' on WikiTree, and the appropriate DNA confirmation statement to enter on any profile with the relationship to one or both parents marked 'confirmed with DNA'.

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@Ellen: That sort of surprise is always fun when some person pops through that actually is a connection. But then how would this be different than going into Gedmatch and finding a 3 cousin? if I knew who their grandparents were it could be easy to identify them here. I've never done this, but I know Gedmatch is particular about sharing private information online, like Wiki. I would think their identity would matter. But then maybe that's why going into ftDNA is so important? I find matches in there all the time...how do I translate those people to my profiles here?

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@Kay: that looks like a great app, but it doesn't recognize that I've logged in. Is this something I need to download somewhere?

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At the bottom of the first page for the app it says that you should log in with the same information that you use for WikiTree. If that doesn't work, there's also a link there to contact Greg Clarke who created the app.

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@Kay. Ok - I'll contact Greg Clarke as my login doesn't SEEM to work. I may just be doing something off.

Thanks for your help.

Amanda

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Away for a day and look at all that happens! Amanda, if you really want self-expression, you should hear me sing. I'm thinking of trying out for The Voice. I mean, when I sing all the dogs in the neighborhood--like up to seven houses away--start barking and going crazy. Neighbors have pleaded with me to stop. They think it's annoying the dogs, but I think they love it! My best performance so far was during a Caribbean cruise a few years ago. Late evening, big crowd, really stormy night at sea driving everyone indoors, karaoke in the main bar. I sang The Wreck of the Edmund Fitzgerald. The audience was positively stunned into silence!

Ahem. Okay; back to business. I hope nothing I wrote earlier made you think that what you had was not a Wiki-useable 3rd cousin "confirmation." Reinforcing again that I can't speak to the WikiTree policy, but you have a sourced paper-trail match to Carolyn, the cM amount falls within a 14% probability as shown at DNA Painter, and so I think that means you should be good to go. And Kay's idea about Greg's confirmation tool is a good one. But someone else needs to speak for the WikiTree DNA Project about policy/guidelines. It's Wednesday, and I'm only ever wrong on Wednesdays. Or was it Fridays? I forget...

Shortly you'll have a private message with an unsolicited and probably useless "care package." Hope you're fine with a ZIP compressed file and that you use Excel. If not, don't bother downloading it.  :-)

There are a few things I routinely do when examining small(ish) segments. GEDmatch is kind enough to tell us the origin (if they know) of the raw data file, and in this case yours is from a MyHeritage v2 test and Carolyn's is from an Ancestry v2 test. Not all AncestryDNA v2 tests are created equal, but the best I can do is assume the "template" of the initial, announced v2 release.

Given that, the net message is that the comparison itself is weak in terms of examining the same SNPs, and that the segment may be a bit longer than advertised. Can't say for sure, but it's a maybe. Taking the Build 37 start and end points of that shared segment at GEDmatch, of the 10,818,299 base pairs encompassed MyHeritage tested 2,280 of them (about 0.021%) and Ancestry tested 2,570 of them (about 0.024%). That's roughly in keeping with the overall percentage of SNPs our microarray tests look at compared to the entire genome.

However, the MyHeritage and AncestryDNA tests examined only 813 of the same SNPs within that segment range. So now we're down to 0.0075% of the segment size. Not much coverage. The GEDmatch free one-to-one analysis tells us that it used 796 SNPs for the comparison, so it excluded a handful of the SNPs in the original raw data (every kit uploaded there goes through a process they call "slimming," where they streamline the size of the data used for final comparisons by removing some of the SNPs they deem to be least useful for the purpose).

I also took a look at 20 SNPs flanking either end of that segment. There were breaks in both cases, but based on what SNPs the MyHeritage v2 test checks, five of the 20 in front of the segment and three of the 20 at the end were also tested at Ancestry. Flipping, six of the first 20 at Ancestry were also tested at MyHeritage, as were four of the last 20 flanking SNPs.

That doesn't inform the comparison that GEDmatch reports; it is what it is. But GEDmatch ended up comparing only 1 base pair every 13,591. Makes me want to get back on my whole genome sequencing soapbox.

Another...well, not anomaly, exactly, but very possibly an illustration of that disparity of SNPs tested by each of the companies, is that I broadened the search to a start locus of 50 million and end of 70 million on Chr 1, and then ran a matching segment search at GEDmatch for both you and Carolyn. You came up with only five "hits," Carolyn with 35. Only one of them did the two of you share in common. He's in the spreadsheet and, all things considered, might be worth contacting.

So... You have a valid match. You have a researched paper trail. You have evidence that the level of the match does not rule out 3rd cousins. I believe (but never trust me on WT policy matters), that you should be able to proceed to "confirmed with DNA" status indicators based on that. And I'll push a few chips to the center of the table and bet that if we had better coverage of that region of Chromosome 1, you might end up actually sharing more DNA with Carolyn than 15.3cM.

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So much of my spirituality and what it sparks begins with this song! It had always been one of my top 3 songs - I live in Chicago, the tip of Michigan. I graduated in History of Religions - Religious Studies from DePaul University - My mentor of the undergrad program was Dr. Read whose primary focus was First Nation history. One of her friends was an Anishinabee Social Worker in Thunderbay Canada. He invited me to a Sweat with him and his Elder in Armstrong Canada, north of Thunderbay. I brought 3 friends and we drove up through Wisconsin into Minnesota. The "highway" becomes a two lane highway as you closer to Canada and it hugs the shore of Superior. On this day a fog had set in. You couldn't see 3 feet in front of you. I was in the backseat and looked out to the right and there - just feet away was a HUGE freighter docked on the shore. It stood about 6 stories high I swear - cloaked by fog. Gordon Lightfoot was humming in my brain - and i just teared. I don't know if anybody else in the car was moved...they were chatting and me? I was haunted. absolutely haunted.

Phillip Landmeier

2 weeks ago

This song has no equal. And while Lightfoot didn't win a Nobel Prize in literature for songwriting, Bob Dylan did. Gordon Lightfoot is Bob Dylan's favorite songwriter. So there is that. Bob Dylan once said that there's only one thing wrong with a Gordon LIghtfoot song: it has to end.

So if some angelic dream possessed you that night - it was your night. I wish I'd been there!

Had to share - I'll look over what you sent. Review your response - but thank you...

Answer 2

I would just like to point out that triangulation is not sufficient by itself to confirm a parental relationship.

Autosomal DNA triangulation on WikiTree is intended to confirm confident parental relationships that have been well documented using genealogical sources throughout the relationship trail between the matching cousins.

The Help for DNA Confirmation has the details.

Comments

Thank you Mr. Kingman.

I am keenly aware of the need for sourcing. The interesting thing about sourcing is how powerful it is when it enhances the point of families bilaterally. By that I mean, I have a well sourced family from the 18th century. There was a source that came to light that might have said something significant about someone in another branch that lived in the area at that time. The trick was that there was an early source for the names of early settlers. 2 fathers came into Savannah port in the same year. with the same name, different wives, but the same name for their sons. One was English planter who settled in Chatham County, the other Flemish weaver from Rotterdam who settled in Highgate. .

The one from Chatham county has all sorts of cool wills and deeds and such. Not so much for the one from Highgate whose community moved up into St. Matthews Parish (Effingham County).

We're beginning to dig out the Weaver whose family was not sourced as their land and counties were not incorporated until well after the Revolutionary War. They did get a church built in 1760, but a lot happens between 1733 and 1760. and that church only documented german based evangelical lutherans ... The Southern Colonies Project has helped enormously...but mapping Chromosomes in Gedmatch for atDNA has been very useful, especially to identify the people immigrating into Georgia after the Revolution and mixing with the early Georgian colonists.

It takes some fancy tapdancing and sourcing and pulling in descendants and such. There have been many surprises looking at who married who and their early pre-Revolution families - and how those names make sense in the other pre-revolutionary Georgian families from the same area. Sourcing was critical in order to to sort out as much who wasn't part of my family.

In Artistic methods this would be called drawing negative space. The image you're looking for emerges out of shading in first what is around what's there.

In my case, it turned out if the document referred to the well sourced family who were planters, well, that wasn't us. ;) That's when mapping chromosomes can become a powerful sourced source...

But you gotta know what you're looking at both on paper as well as Science. I've seen sources misapplied more than once in my tree to shoehorn one family into another. Applying paper before you get the history of the area can be a problem.

This is exactly why a global tree makes sense. The fact that there is more than one set of eyes, brains and talent to correctly interpret the information in order to work any given profile to me is as important as the paper. Must include the history and science.

There certainly is a lot more than either JUST DNA or paper sources to find the truth behind a profile. I have yet to see a panacea in genealogy. If anybody knows of one, I'd appreciate if you'd let me know?