Your TGs are pretty unique!

A Triangulation Concept

I often get questions along the lines of: “do my Matches have the same TGs?” or “can I form TGs for my 11 kits in one spreadsheet!” The answers are an emphatic: “NO!” and “NO!” Most of us are pretty ego-centric with our DNA analysis – and this is good! And while we are the center of our own universe of DNA segments, each of our Matches is, likewise, the center of their universe of DNA segments. Each of us gets random segments of DNA from our ancestors – random size segment(s) and random placement somewhere on our chromosomes. Once we get past the 2C (2nd cousin) or 3C level, it is quite amazing that we share DNA with more distant cousins at all. But we have many, many cousins, and many of them beat the odds and we share a DNA segment.  However, this does NOT mean that we and a Match both got the exact same DNA segment from a Common Ancestor (CA) – that very rarely happens.  We get a segment, and our Match gets a segment, and what we “see” in a Chromosome Browser is the portion of our individual segments from the CA that overlaps – the shared part of our segments. When we form a TG with various Match-segments (most matching each other), there are usually fairly well defined start and end locations to the TG*. Of the shared segments in a TG: some will start at the start of the TG, and end before the end of the TG; some will end at the end of the TG; some will “float” within the TG; and some, particularly with closer cousins, will be larger than the TG. These are all normal and expected [see an example in Figure 6 here]. The point of this concept is that each of the Matches in the TG will have their own unique TG – representing the full segment they got from the CA. If your shared segment with a Match, aligns with the start location of a TG, there is a very good chance that the Match’s segment from the CA began before yours did, and the Match’s TG has an earlier start location. Try this experiment: Take two (or more) Matches at GEDmatch with shared segments that start at the start of one of your TGs, and compare them to each other. Often their overlapping segment will start before your TG. In fact, using the Shared Segment search utility at GEDmatch, you can probably find other Matches that match in a Match’s TG, that don’t appear in your TG (and those Matches have segments that don’t overlap enough with your DNA to form a shared segment). The bottom lines for this concept are that Triangulation should be done on one “base” person (usually you) at a time; and there is more to the DNA passed down from an Ancestor than what is shown by any one descendant’s TG. Each of our TGs are pretty unique, and our Matches will not have the same TGs or chromosome map.

[*Sometimes the TG start and end locations are a little fuzzy (see here), but our focus should be on the bulk of the TG.]

08A Segment-ology: Your TGs are pretty unique! Concept by Jim Bartlett 20170907

A Triangulation Overview

A Segment-ology TIDBIT

Triangulation is a tool. It’s a process that can help us with our genealogy. It is not the only tool in our kit bag – there are many other tools that also utilize DNA, including InCommonWith Lists, Matching Segment Lists, Matrix displays, Shared Matches, Clustering, Circles, etc, etc. This blogpost is an overview of Triangulation.

With atDNA we have been using Triangulation to mean two different things:

Segment Triangulation of shared segments (a focus of this blog), and

Ancestry Triangulation (having at least 3 Matches in a Triangulated Group (TG) all match on the same ancestral line; sharing a Common Ancestor (CA) on that line.

In the atDNA community we often conflate these two concepts, and they are very much intertwined. I tend to think first of forming a TG and then looking at the genealogy to determine the side (maternal or paternal) and then finding various MRCAs. But some start with the genealogy and look for Triangulation to add evidence that a CA is correct. Both ways will work, they are intertwined in genetic genealogy, so in this overview I will also conflate them. Here are some overview points about Triangulation:

We look for at least 3 Matches, Much of our work as genealogists involves one-on-one – finding a Common Ancestor with a Match – that’s OK, but it’s not Triangulation.

We look at overlapping DNA segments. ICW and other tools don’t require overlapping segments – that’s OK, but they are not Triangulation.

We look for 3 “segment” legs. This means the 3 people (usually you and two Matches) that form a Triangulated Group are not closely related. But once a TG of 3 cousins is formed, other close relatives can be added to the TG. It’s the TG forming that needs 3 strong legs. So 3 siblings and their parent do not form a TG, but they can be in one.

The shared segments that form a TG must be IBD. From experience we’ve found that:

  • “all” shared segments over 15cM are IBD;
  • shared segments under about 7cM are false most of the time; and
  • the process of comparing overlapping shared segments in a TG will cull out many in the 7 to 15cM range which do not match – I consider these to be false segments.

Blaine Bettinger is working to define Triangulation – not to preclude the use of other tools – but to help us better understand Triangulation as a tool. I use Triangulation as a tool to primarily sort and group all of my IBD segments. I’ve formed about 400 separate TGs over my 45 chromosomes. New Matches always fall into one of these TGs (close Matches may span two or more TGs – it’s OK). This is segment Triangulation. With close relatives, I’ve been able to determine the side for these 400 TGs. This is a huge benefit because new Matches almost always Triangulate with other Matches already in a TG; and I then know which side our Common Ancestor must be on. This is an excellent use of the Triangulation tool.

Ancestry Triangulation does not preclude me from also using the information of Circles, or ICW lists, or ethnic makeup, of even genealogy records or Trees or discussions with Matches to determine CAs.

Within a TG we may find a CA with a Match. As we have pointed out many times: shared DNA plus a CA does NOT mean that the shared DNA came from that CA, or that the CA is somehow “proved” because there is also a shared segment – maybe, but also maybe not. But, by finding 3 Matches in a TG who all share the same CA (Ancestry Triangulation), we increase our confidence (not “prove”) that the CA is linked to the shared segment; and with more Ancestry Triangulation (and/or walking the ancestor back), we increase our confidence even more.

If Triangulation leads to a conclusion that a CA is not linked by the shared DNA, we can still be cousins on that CA, and we can still use ICW, Circles, etc. to pursue a genealogy goal. But we should not say that DNA supports that cousinship conclusion.

IMO, a TG has characteristics that help us in our genealogy goals. Triangulation is a strong tool that takes advantage of our shared DNA with Matches.

I applaud Blaine’s effort to try to define Triangulation and provide some standards for its use.

The above is adapted from my recent post to the Genetic Genealogy Tips and Techniques Facebook Group.


[22N] Segment-ology: A Triangulation Overview TIDBIT; by Jim Bartlett 20170728

Triangulation at 23andMe

A Segment-ology TIDBIT

23andMe has a great feature. It starts out as a standard In Common With (ICW) list for each Match you are sharing with (old Shared Genomes Matches and new Open Sharing Matches). This ICW list is near the bottom of your Match’s page. But the difference with other ICW lists is the Shared DNA column. The Matches marked with a “Yes” have overlapping segments – and over 99% of the time they form a Triangulated Group (TG).

So go to your DNA Relatives page and scroll to the bottom and click on the “Download aggregate data” link. You’ll get a spreadsheet of all your matches and most of the 23andMe data. Sort the spreadsheet, and delete the ones with no segment data. Then sort on Chromosome Number and Chromosome Start to put them in a particular order. Add a column called “TG ID”. Now you’re all set to begin Triangulating.

Start with the first Match in the spreadsheet (let’s call it A). Click on the hyperlink* that takes you to A’s page, scroll down to the ICW list and note in your spreadsheet Match A and each Match with a “Yes”. Since you are starting on Chr 01, call this TG: 01A, and put 01A in the TG ID column for A and each “Yes” Match. This pretty much identifies all the other 23andMe Matches that are in a TG with (A). The whole TG 01A (of 23andMe Matches) is created through one Match! There may be a few that don’t overlap A enough to form a shared segment at 23andMe, but all you have to do is go down your spreadsheet list of 23andMe Matches and select the next Match (B) that is not already in a TG; click on B’s hyperlink and look at their ICW list for “Yes” Matches with (B) – some will either overlap with (A) (call all of them 01A, too); or they all form a new TG (say 01B) – one or the other. Then continue with the next Match not already in a TG.

One could probably go through their entire 23andMe list of shared Matches in a few hours, creating TGs for all of them. There may be some with no ICW “Yes” Matches – give them their own TG; and move on. Be careful with Matches with more than one shared segment – make sure to treat each segment individually – this may take a little extra analysis.

Remember, TGs represent segments (from an ancestor) on one of your chromosomes. They are equivalent to phased data. I consider all shared segments at 23andMe which Triangulate to be IBD. All of them should be in a TG on one side (parent), or the other.

If you have known relatives in any of the TGs you can assign those TGs as Paternal or Maternal. This often allows other, overlapping TGs to also be assigned to a side, using logic.

*Note1: clicking on the 23andMe hyperlink (Link to Compare View) is a little tricky – I usually just copy (Cntr-C) the spreadsheet URL, and paste (Cntr-V) it into the URL bar of any open 23andMe page – hit Enter. It goes pretty fast.

Note2: feel free to use any TG ID numbering system you want. I think it’s wise to start with the Chromosome number. But you can name your TGs Bill, or Bob, or Sue if you want. You are creating groups that will tie to ancestral lines.

ARE YOU READING THIS FTDNA? ALL YOU NEED TO ADD IS A YES!! And AncestryDNA could add a similar feature, and hell might freeze over, too.

Enjoy easy Triangulation at 23andMe…


[22M] Segment-ology: Triangulation at 23andMe TIDBIT; by Jim Bartlett 20170720

Using a Child to Determine the Side

A Segment-ology TIDBIT

Normally your child’s atDNA cannot indicate which side of your DNA a Match is on. But, a child only gets one side of your DNA at a time. In other words: you have DNA from both of your parents that covers each of your chromosomes from beginning to end; but you can only pass on one side to a child. Your parents are your child’s grandparents – every bit of your DNA passed to a child is either one of the child’s grandparents (your parents) or the other. Please review Bottom-Up and Crossovers to see the approximate 34 crossover points that divide all of your child’s DNA into about 57 segments from your parents. This is a very important concept in atDNA, and well worth the time to study it until you understand it.

So if you have a segment that you cannot figure out which side it’s on (your maternal or paternal side), having a child also match on that segment doesn’t give you any insight. Because: if you don’t know which side it’s on for you, you don’t know which grandparent it’s on for your child.

However, if you have tested at multiple companies, a child may help. Here is an example.

At 23andMe I have 3 Matches who all match me and each other on the same segment – a Triangulated Group (TG). There are no other 23andMe Matches, or any known cousins, who overlap this segment at 23andMe. However at GEDmatch I have a number of Matches with overlapping segments, and I’ve formed two TGs. And with my Dad’s kit at GEDmatch, I know which TG is paternal and which is maternal. I also have a child at GEDmatch, and he matches the maternal TG, but not the paternal TG. So my son got my maternal DNA for this segment. This son was also tested at 23andMe, so checking the ICW list with the 3 Matches above, they all include my son with a “Yes” – meaning an overlapping segment. So I can conclude that the 3 Matches at 23andMe form a maternal TG for me, because my son only got my mother’s DNA on this segment.

This now lets me communicate this information to each of the 3 Matches: our Common Ancestor will be on my mother’s side (and I include a list of Patriarchs of those lines in my message). I’ve made up two standard messages for 23andMe Matches – one for each side – which I can quickly copy and paste into the 23andMe message box. I initially get about 10-20% response – usually with a thank you for providing a concise, and easy to review list of potential Common Ancestors. Over time, additional responses trickle in. It’s a quick and easy way to find those Matches you can work with. And sometimes these “seeds” bear fruit months and even years later.


[22L] Segment-ology: Using a Child to Determine the Side TIDBIT; by Jim Bartlett 20170712


Amount of DNA vs Number of Matches

A Segment-ology TIDBIT

There are two concepts at work here – each is different – keep them straight and separate. Each in it’s own way can provide insights.

1. Amount of DNA from Ancestors. Although DNA from your Ancestors is random, there is some uniformity. You get exactly 1/2 of your atDNA from each parent; pretty close to 1/4 from each grandparent; about 1/8 from each great grandparent. By the time you get to your 128 5G grandparents, the average will be 1/128 from each one of them (roughly 1 percent), but with each generation past your parents, the deviation from the average increases. Still – the total of all ancestors at any generation will sum to 100 percent. On average you got about 15cM from each 5G grandparent, which may be in one segment or spread over several segments. The companies report that, in general, you will not share enough DNA to match most of your 6th cousins; but we know that you have so many 6th cousins that you will share with many of them – experience shows you will share from 0-21cM with some your 6th cousins. [see The Shared cM Project 2.0 at ]

2.Number of Matches from Ancestors. This depends on several factors: Number of cousins, who tests, endogamy, etc.

A. The number of cousins you have from each Ancestor is directly related to the size of their families leading to the number of their living descendants. Larger families => more cousins => more Matches.

B. Similarly the number of cousins you have from each Ancestor is directly related to how far back that Ancestor is. Distant Ancestors => more cousins => more Matches.

C. Who tests. This may be most pronounced with recent immigration. The more recent an Ancestor immigrates, the fewer number of living descendants in the US, where the highest percentage of atDNA test takers live. Recent immigration => fewer cousins tested => fewer Matches.

D. Endogamy. With endogamy, the amount of shared DNA increases, resulting in many more Matches who otherwise might not have matched. The classic case is Ashkenazi Jews, who tend to get many times the number of Matches others get, and the Matches are in fact somewhat more distant than indicated. This also applies to other endogamous populations. Endogamy => more cousins => more Matches.

Some of my experience and observations

My maternal grandmother was from immigrants to US in 1850s. Roughly 1/4 of my atDNA is from her, and 1/4 of my Chromosome Map has TGs from her line. But, I get relatively few Matches on this 1/4 of my Ancestry, and some of the “gaps” in my Map have no Matches in them at all. When I get only 1 or 2 Matches in a TG on my maternal side, it’s pretty certain they are from my grandmother’s line. The other maternal TGs are from my mother’s paternal side with deep Colonial Virginia roots – they tend to have many Matches.

As the Matches pour in, and are added to my TGs and Chromosome Map, I can see where some TGs have many Matches and must come from distant Ancestors – perhaps at the limits of my Tree, or beyond – so I focus on the closer MRCAs (Most Recent Common Ancestors) which provide pointers. In some cases I’ve found the Ancestor had a Plantation and raised many children.

Some of the other TGs have small to medium numbers of Matches, and where I can find an MRCA, they tend to be smaller Colonial families – folks who moved around a lot; died earlier in life; and/or had few known children who survived.

So as you form TGs, and look at the resulting Chromosome Map, they start to paint a picture…


[22K] Segment-ology: Amount of DNA vs Number of Matches TIDBIT; by Jim Bartlett 20170517

Format for AncestryDNA Notes

A Segment-ology TIDBIT

Here is an example of the format I usually use for AncestryDNA Notes, line by line:

[1] 6C1R: BUTCHER/BUSH > Valentine

[2] Gm 123456 [03F25] 15.1cM

[3] 12.4cM/1Seg

[4] SM: 6 [1 is 4C on BUTCHER]

[5] m5/4/17; mr5/5/17w/Gm#

[6] Added to xls & Notes

[1] is just line number, you don’t need to type that in

6C1R is 6th cousin once removed; 4Cx2 is double 4C

BUTCHER/BUSH is our MRCA surnames > Valentine is the child my Match descends from

Gm is GEDmatch ID

[03F25] is my Triangulated Group ID [Chr 3; F means start in 50-60Mbp range; 25 are first two Ahnentafel numbers of my ancestry to the MRCA – in this case my father and his mother]

15.1cM is cM per GEDmatch

12.4cM is cM per AncestryDNA [almost always smaller]

SM = Shared Matches; then the number of them; then any key info about any of them [in brackets]

M5/4/17 means I posted a message; mr means reply

Added note confirms info was added to my spreadsheet and my Notes on each surname

This info is available by hovering over the little document icon next to each Matches name. It is very useful in its own right to help me keep track of each Match. It is also particularly valuable when reviewing a list of Shared Matches – you can easily see which ones you have notes for and what the notes say. This helps you decide if a group of Shared Matches are grouping around one ancestral line.

I do this pretty religiously for all Matches with Hints; and try to do it for all 4C Matches, too – no time is left for the tens of thousands of other AncestryDNA Matches.

[22I] Segment-ology: Format for AncestryDNA Notes TIDBITS; by Jim Bartlett

One Segment at a Time

A Segment-ology TIDBIT

The old saying: How do you eat an elephant? One bite at a time. We can, and should, apply this advice to Triangulated Groups and Chromosome Mapping. Take it a TG/segment at a time.

These days, the Matches are pouring in, and it’s easy to get overloaded with data. So I’m setting two goals:

  1. Form one new TG every day
  2. Communicate with the Matches in a TG each day

Each person’s objectives and available time are different, so set the timeframe to suit your own situation (every other day, each week or whatever). The point is to put a goal and plan in place.

There are about 400 TGs spread over my 45 chromosomes. So at one-a-day, it would be March 2018 before I could form every TG for my Dad (I’m just getting started on his chromosome map).  But by then this long ignored project would be done; and his map would provide extremely valuable information for my chromosome map.

And if I send out a small group email (average 10 Matches) to the most significant Matches in a TG every day, it will be March 2018 before I focus on every TG. But two good things will happen: 1) I will have focused on every TG, and worked on the Common Ancestor; and 2) For about every 10-20 emails/messages I send out, I determine a new Common Ancestor. So by March 2018 I’ll have another 200 or so Common Ancestors. [NB: Each CA is not necessarily the correct genetic link for the TG, but they are all genealogy cousins and provide important clues in our quest to “walk the ancestor back” and/or obtain multiple agreements on the TG CA.]

In other words, we reap what we sow – we get a percentage return on the communications we send to Matches – the more we send, the more we get in return.

Again, everyone’s situation is different. All I’m suggesting is to set a goal, and schedule some time for TGs and chromosome mapping. Take a periodic bite out of the atDNA elephant!


[22H] Segment-ology: One Segment at a Time TIDBIT by Jim Bartlett 20170218