How to Triangulate your Matches

Video Transcription

You have thousands of matches, but where should you start as far as looking at them? How do you know which ones are going to be the ones that you’re gonna be able to find out are actually related to you? Well, I’m gonna show you a tool that might be able to help you out.

Howdy,  I’m Andy with Family History Fanatics, and this is a segment of DNA. Be sure to subscribe to our channel and click on that bell if you’d like to be notified about upcoming episodes. You may have heard of triangulation in relation to genealogy or DNA and are wondering what does that mean? Triangulation is a way that we can group a set of matches and know that they are related through a common ancestor. Now, if you know a group of people is related through the same common ancestor and maybe a little bit about how some of them are related, then you can focus your research on those direct lines as opposed to trying to look at all of your different lines of where they might fit in. So simply match A has to match match B, and then match B has to match match C, and then match C has to match match A.

Now these are three different matches, at least three different matches. They all match each other, but this is not enough. The most important part of triangulation is that all three of these have to match each other on the same segment. If they match on different segments on different chromosomes, then the group’s not triangulated. You still may be related to a common ancestor through them, but that’s not a triangulated group. If they match different segments on the same chromosome and maybe those segments are adjacent to each other, it’s still not a triangulated group. You still may have a common ancestor with all of those people, but it’s not a triangulated group. But when you have the same segment that is matched by everybody in that group, then that segment was passed down by a common ancestor. And what you’ve basically formed here is you formed this triangle where everybody is equal to everybody else, hence the name triangulation.

Now,  I started off with just three people, but you can have a triangulated group with multiple people, 5, 6, 10, 20 people. The key is is that everybody has to match everybody else. It’s not good enough that you match all of them. Everybody has to match everybody else. In most cases, triangulation indicates that you share a common ancestor because that segment that you all share together had to have been passed down from preceding generations. Now, there are a few special cases where a triangulated group doesn’t share a common ancestor, but those are really rare. So from your match list, if you can start creating triangulation groups, then you’re gonna be well on your way to actually identifying common ancestors you share with those particular matches. Now, in the GEDmatch tier one, there is a tool that you can use to help speed up this process. There’s ways to do this manually, and I’ve shown some of those before on the YouTube channel, but the GEDmatch tier one tool speeds up this process greatly for you.

I’ve logged into my GEDmatch account, and as I scroll down, you’re going to be able to see the different tools. Now, the free tools are in DNA applications, and that’s not the one we’re going to use. There is a way that you can do triangulation using these free tools. It takes a lot more time and a lot more effort. But the one that we want to look at is down in the tier one and it is called triangulation. Now, on the triangulation page, there’s going to be some information that you have to enter in. So first off, you have to enter in a kit number. So I’m going to put in one of my kit numbers. Next is what is the maximum number of close match that you want to look at? Now, you should have an idea on your match list of how much DNA you share out to, you know how many matches.

So for instance, if you have a lot of people that share a lot of DNA, let’s say 20 or 30 or 40 centimorgans or more, and it is in the hundreds or maybe even in a thousand or a couple thousand, then you might want to go with a higher number For people who don’t have that many closely shared matches, then you probably wanna stick with a default of 500. The more that you go, the longer it’s going to take, but you might have more triangulation groups that are created from that. The next thing is the upper segment threshold limit. This is the people that you want to exclude really from your triangulation groups. For instance, right now it is set as a default at 3000, which means that everybody, except for my parents and my twins are going to be included in this analysis. Now, why you might not want to do this is because your siblings are gonna be included.

Now, you share a lot of DNA with your siblings, and because you both have that common parent, there’s going to be a lot of triangulation groups between you one sibling and some other match. In fact, your sibling triangulation groups are going to be the vast majority of these. So I usually like to make sure I lower this to eliminate siblings and in fact eliminate a lot of close relatives. So if I put this at 2100, it’s going to eliminate siblings, but it’s going to still have grandparents, aunts, uncles, and of course my cousins. Now again, I still share a lot of DNA with all of them and even with my grandparents. For instance, if I’m doing triangulation through my grandfather, well, it’s just me and my grandfather. Technically it is triangulation because we both got that same segment of DNA with whatever third match that there is.

However, it’s not really a good check of it because it’s really just between my grandfather and that match. So I can lower this even further. At 1500, I’m only gonna have a few of those aunts and uncles and grandparents. I like to actually lower it down to 1100 or even to 500. At 500, you’ve eliminated most of your first cousins. If you’re particularly looking for people on your mother’s side or your father’s side, you might not want to eliminate your first cousins because that will tell you automatically where that match is going to be on your mother’s side or your father’s side. However, it’s still going to produce a lot of triangulation groups. So starting out, I’d actually go with lower and start to build up from there.

Next in line is the minimum segment length. I usually never change this. I keep this at the 7 centimorgans as a minimum. Now if you are part of an endogenous population, you might want to increase that to 15 centimorgans or more. The next we have what chromosome you want to triangulate on. Now you can do all of them, and that’s going to give you all your different triangulation groups. Or you can do a particular chromosome if you are already researching something that maybe a match that you have on a particular chromosome. So for this, I’m just gonna look at chromosome one. It’s gonna take less time to run right now, and you can always do it as many times as you want with a tier one membership. I the build the same at the default of build 37. Next is the different display options, and there’s two options.

Then show the results sort of by the chromosome segment and the start position and then show the results sort of by the kit number, the chromosome segment, and start position. I like to show it both ways, but if you want to just look at one way after you’ve seen it, then that’s fine. Now we’ll get into cross matching after I show you this initial search. So I’ve set up all of my options. I’m going to submit, and that’s going to give me my triangulation list. So right now what it’s doing is it’s going through and it’s analyzing the kits. There’s 500 kits that it’s analyzing, and you can see the progress on the little asterisks as they appear down below. Once it’s done processing, it’s going to come up with this match list. Now, a couple things about this match list that’s different from others is this is a triangulated match list.

So you’re actually matching with two people. So for instance, there’s going to be a kit one, which is one person that matches you, and there is a kit two, which is another person that also matches you. But that kit two also matches kit one. So as I go and scroll over, what it’s going to give me is it’s going to give me the start and the end location, how long of a segment that is, and then a little representation of where that is on the chromosome. So you can see that there’s these first few that are scattered throughout the beginning part of the chromosome. And then it looks like I have a big chunk of people who are all in the same part of the chromosome. Now, I mentioned before that there is cross matching. So let’s go back to cross matching and see how that is a little bit different because right now each one of these lines represents one triangulated group. You’ve just matched between the three people. I’m going to do everything the same except this time I’m going to click on the cross matching box. And what this is going to do is not only is it going to look at just those three people, me and then two matches together, but whenever there is a segment that is similar to another segment, it’s also gonna add in that person.

Let me show you what I mean by that. Now, before all of these segments were the same color. They were green because it was just looking at each individual one. But now as I go through, I can see that some of these are green, which is clearly just those three people are triangulated. But then there’s a group that we saw before that’s all around the same segment. Well, all those segments also triangulate with each other. So this isn’t a group of three people. This is a group of, it looks like almost 50 people altogether. Now we can see down here at the bottom there is another segment, this little green segment right here that it overlaps this, but it’s not colored red, so it doesn’t triangulate. With that, we can see that this also overlaps with this next one, which is orange, and it doesn’t triangulate with that.

So this is a separate group than these other ones. So using cross matching allows you to take your triangulated segments and then even further group those into a cluster of people that are going to share a common ancestor with you. Triangulation is a great way to help focus your genetic genealogy research because now you have a group of people that you know have to be related through a common ancestor, and you can communicate with those people and find out share trees and see where your families may match up together. If you have any questions about how to use the GEDMatch tier one tool for triangulation, put it in the comments below and I’ll try to answer it. And if you like this video, be sure to give it a thumbs up and share it with all your friends.