DNA triangulation question I know not another one

+7 votes

Sorry for asking the same quiestion I know many of you have answered 100's of times. I have tried to read a bunch of the other DNA triangulation questions to learn but I have not seen this spoken about   I also want to know if a lower cM is allowed for more distant relationships. The closest relationship is 5 steps (4th  cousins once removed). 

I have not use itentifying names and kit numbers because all the parties to this triangulation have not been contacted. I have not read about having permission from the other parties but I think that is something you should do.  

First here are the relationships as defined by WikiTree

Carolyn and Janice  are 4th cousins once removed - ICW  [[Boggs-595|James Clendenin Boggs]]
Nancy and Janice are 5th cousins twice removed - ICW  [[Boggs-47| Charles Francis Boggs]]
Nancy and Carolyn  are 6th cousins once removed - ICW [[Boggs-47| Charles Francis Boggs]]

Next I ran a Multiple Kit Analysis on all 3. I had listed Carolyn first. I then looked at the 2d Chromosome browser.  It showed we shared  a 3.474 cM segment on chromosome 3 from 185115117 - 187126148. (smallest share is from Carolyn)   I then repeated this whole thing over  but ran Janice first and again running Nancy first. On both Janice and Nancy it shows New Root on Chromosome 3.

I am now very confused.  Is this normal?  

I remembered reading that you also had to do a one to one so I ran that next. 

Nancy to Janice
Chr    Start Location    End Location    Centimorgans (cM)    SNPs
11    31,879,294          40,845,302               11.2                  2,434

Nancy to Carolyn
 Chr    Start Location    End Location    Centimorgans (cM)    SNPs
3          184,246,274    193,571,219              21.7                  2,507

Carolyn to Janice
Chr    Start Location    End Location    Centimorgans (cM)    SNPs
3          185,115,117      187,126,148           3.4                     536


  I understand Nancy and Janice match Carolyn I am just confused why we dont match any other way.  Wow I am so lost  

in Genealogy Help by Mel Lambert G2G6 Mach 3 (32.1k points)

4 Answers

+5 votes
Best answer


With what you are showing us, you do not have a triangulated match.  As Phil stated, Nancy and Janice share a decent segment on chr. 11.  For a triangulated group on that segment, you need a third person to share a 7+cM segment within that start/stop of 31-40 (abbreviated start & stop points).

Nancy and Carolyn share a good sized segment on chr. 3.  It has nothing to do with the segment that Nancy and Janice share since it's on a different chromosome.  The segment that Carolyn and Janice share on chr. 3 is too small (being only 3.4cM) to use as part of a triangulated group.  You need 7+cM.

Have you read articles about triangulation?  If not, you need to do that to gain a better understanding of what you need to do and have for a triangulated group.  I recommend ISOGG (International Society of Genetic Genealogy) for learning about DNA.  For autosomal, start at this page:  http://isogg.org/wiki/Portal:Autosomal_DNA .  There are many links to articles there that should be helpful to you.

Triangulating groups and mapping chromosomes is very detailed and can get quite complex.  You need to fully understand it to be successful with it.  If you decide to proceed further, using it to help you prove ancestors for connections you have no idea about (as opposed to the cousins you mention), I would recommend you start with the matches you have that share the largest segments with you (which means your common ancestor is fewer generations away) as opposed to smaller segments.  You have a greater chance of determining your common ancestor with the closer cousins.  If you start with the small ones, you might get frustrated and give up completely.  But don't do that!  As the years pass, more and more people will test, more and more people will get a family tree together (hopefully with Wikitree so we can all see their ancestors), and it will become easier to work together and find the MRCA (most recent common ancestor) with your matches.

You asked about why you don't match 'any other way'.  You're going back pretty far with a 5th cousin 2x removed and a 6th cousin.  I always say that DNA is 'fickle'; by that, I mean that it gets passed on quite randomly (autosomal).  Even siblings will one get certain segments from a parent and others not, so you can imagine once you've added several more generations to it how random it can be as to whether or not you are sharing a small segment (which is what it would be when you get back 6 generations generally).

Good luck, and feel free to continue asking questions.  I'm happy to answer any personal messages I get with regard to DNA as well...

by Darlene Athey-Hill G2G6 Pilot (471k points)
selected by Kay Wilson
+3 votes
I get confused on the triangulation criteria too.  But the point is, as I get it, that you want to come at a common ancestor from two (or more) different directions so that the odds of "hitting" a known common ancestor at random is small, and thus the odds that this is indeed a confirmation of the paper genealogy is high.  And that brings up the problem of  using your Carolyn to Janice 3.4 match to confirm a relatively close connection.  True there is a likely connection somewhere in the past, but it might be much earlier than the supposed connection and be from the background gene pattern of people from a given area.  so the actual source of the connection might be from hundreds of years before you thought.  As you get more and more matches from different relatives, the odds of a true match with a common ancestor improves and you'll be more certain of what a match means.You probably need to do what I also need to do and take the hundreds of matches on GEDmatch one to many and sort out those who have matches on particular areas of particular chromosomes and contact them to see if they have common known ancestors with you.  Since GEDmatch gives you an e-mail address, it's likely you will get good interest from those you contact.  Note that you can compare two different people who match you in a particular location and they might have connections with each other that you don't have with either.  Ok, now you have me ready to go back and start sorting out more of my matches.
by Dave Dardinger G2G6 Pilot (410k points)
+3 votes


It takes some time to figure out all of the material - and some of the information is not presented as well as it could be.

I am working through several formats that I think will help me - all of the analysis is being done in GEDMatch.

I am putting the material on a Free Space page.

Here is an example Evans Patterson Bryant MLJ Soul 3 Way DNA Confirmation

by Philip Smith G2G6 Pilot (311k points)
+4 votes
Mel, this may be stating the obvious, but you do not show a triangulation with your one to one runs. Nancy has nice strong matches with both Janice (on Chr 11) and Carolyn (on Chr 3). If the one to one for Nancy to Janice does not show a match at the correct segment of Chr 3 (assuming you set your limits low enough), then the 2d browser results must be in error.  While I like the SNP strength of that Carolyn to Janice match, many people would suggest you search for a stronger cM match elsewhere to corroborate your WikiTree linkage.
by Phil Kuhn G2G2 (2.8k points)

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