Using DMT, Part 1: My 23andMe Data - Thu, 17 Oct 2019

I am going to show you how I am using Double Match Triangulator, and some of the information it provides, at least for me.

My own DNA match data is difficult to analyze. I come from a very endogamous population on all my sides that originates in Romania and Ukraine. The endogamy gives me many more matches than most people, but because my origins are from an area that have scarce records prior to 1850, I can only trace my tree about 5 generations. Therefore the vast majority of my matches are with people I may never be able to figure out the connection to. But there should be some that I can, and that is my goal, to find how I’m related to any of my 5th cousins and closer who DNA tested.

I’ve tested at Family Tree DNA, 23andMe, Ancestry, MyHeritage, and I’ve uploaded my DNA to GEDmatch. I have also tested my uncle (father’s brother) at Family Tree DNA and uploaded his DNA to MyHeritage and GEDmatch.

Ancestry does not provide segment match data, so the only way to compare segments with an Ancestry tester is if they’ve uploaded to GEDmatch.

Where to Start

With DMT, the best place to start is with the company where you have the most DNA relatives whose relationship you know. I know relationships with:

• 14 people at Ancestry, but they don’t give you segment match data
• 9 people at 23andMe.
• 3 people at GEDmatch.
• 2 people at MyHeritage.
• 2 people at Family Tree DNA

So I’ll start first with the 9 people at 23andMe. The somewhat odd thing about those 9 people are that they are all related on my father’s side, meaning I won’t be able to do much on my mother’s side.

We’ll see what this provides.

Getting Segment Match Data from 23andMe

At 23andMe, you can only download the segment match data of people you administer. That means you have to ask your matches if they would download and send you their match data if you want to use it.

But there is an alternative. If you subscribe to DNAGedcom, you can get the segment match files of any of the people you match to. I have a section of the DMT help file that describes how to get 23andMe match data.

I used DNAGedcom to download my own segment matches, as well as the segment matches of the 9 relatives I know relationships with at 23andMe, plus 7 other people I’m interested in that I don’t know how I’m related to.

Entering my Known Relatives’ MRCAs in my People File.

First I load my own 23andMe match file as Person A in DMT. Then I run that file alone to create my People file. DMT tells me I have 8067 single segment matches. DMT excludes those that are less than 7 cM and produces a People file for me with the 892 people who I share 4244 segments of at least 7 cM. It is sorted by total matching cM, highest to lowest so that I can see my closest relatives first.

I go down the list and find the 9 relatives I know and enter our Most Recent Common Ancestors (MRCAs). Here’s the first few people in my list whose names I altered to keep them private:

Naa is the daughter of my first cousin, i.e. my 1C1R. She is my closest match at 23andMe and we share 541 cM on 22 segments that are 7 cM or greater. Our MRCA from my point of view is my Father’s paRents, so I enter FR as our MRCA.

Daaaaa Paaaaa is my father’s first cousin sharing 261 cM. So he is also my 1C1R but since he is my Father’s Father’s paRent’s daughter’s son, he gets an MRCA of FFR.

Similarly, Baaaa Raaaaaa and Raaa Raaaaaa are brothers who are both 2nd cousins sharing 153 and 143 cM with me. Their MRCA is FFR. 

The other two people I marked FFR are my 2C1R sharing 152 cM and 94 cM.

I also have 3 people related on my father’s mother’s side. The two FMFR’s shown above are 3rd cousins on my father’s mother’s father’s side sharing 90 cM and 84 cM. Also on line 96 (not shown above) is a 3rd cousin once removed sharing 58 cM who I’ve given an MRCA of FMFMR.

Single Matching

I save the People file with the 9 MRCAs entered, and I’ll run that file alone again. This time, it uses the MRCA’s and paints any matching segments at least 15 cM to the MRCA ancestral path.

This is exactly what you do when you use DNA Painter. You are painting the segment matches whose ancestral paths you know onto their places on the chromosome.

The reason why single segment matches must be 15 cM to paint is because shorter single segment matches might be a random match by chance. That can be true even if it is a close relative you are painting. It’s better to be safe than sorry and paint just the segments you are fairly certain are valid. Beware of small segments.

DMT tells me it is able to paint 15.3% of my paternal segments to at least the grandparent level using the 9 people. My closest match, my first cousin once removed doesn’t help directly, because some of her segment matches may be on my father’s father’s side, and some may be on my father’s mother’s side, and we can’t tell which on their own. But her matching segments may overlap with one of the other relative’s matches, and hers can then be used to extend that match for that grandparent. DMT does this work for you.

With this data, DMT cannot paint any of my maternal segments. I’d need to know MRCAs of some of my maternal relatives at the 2nd cousin level or further to make maternal painting possible.

DMT produces a _dnapainter file that I can upload to DNA Painter. This is what it looks like in DNA Painter showing the 15.3% painted on my paternal chromosomes:

My father’s father’s side (in blue), could only be painted to the FF level because I don’t have any MRCAs beyond FFR.

My father’s mother’s side (in green), was paintable to the FMFM level because I had a 3C3R with an MRCA of FMFMR.  But there’s less painted on the FM side than the FR side because my FM relatives share less DNA with me.

Double Matching and Triangulating

Now let’s use the power of DMT to compare my matches to the matches of my 9 known relatives and the 7 unknown relatives, combine the results, and produce triangulation groups and finally produce some input for DNA Painter.

The great thing about triangulating is that by ensuring 3 segments all match each other (Person A with Person C, Person B with Person C, and Person A with Person B), it considerably reduces the likelihood of a by chance match, maybe down to segment matches as small as 7 cM, which is the default value for the smallest segment DMT will include.

This allows DNA to paint 46.1% of the paternal DNA, about 3 times what was possible with just single matching. In DNA Painter, this looks like:

Clusters

DMT also clusters the people I match to according to the ancestral paths that the majority of their segments were assigned to.

DMT clustered the 892 people that I match to as follows:

There were 83 U people who DMT could not figure out if they were on the F or M side. There were 75 F people who DMT could not figure out if there were on the FF or FM side. And there were 19 X people who didn’t double match and were only a small (under 15 cM) match in my segment match file, so these were excluded from the analysis.

Overall 63% of the people I match to were clustered to my father’s side, 24% to my mothers side. Here’s how my closest matches (see first diagram above) look after they were clustered:

So it looks like quite a few of my closest matches whose MRCA I don’t know might be on my FF side. That tells me where I should start my search for them.

There are also 4 matches that might be on my M mother’s side that I can try to identify.

All but two of my top matches have at least one segment that triangulates with me and at least one of the 16 people whose match files I ran against. All the details about every match and triangulation are included in the map files that DMT produces, so there’s plenty of information I can look through if I ever get the time.

Next post:  GEDmatch.