Much like the mathematical and geometrical triangulation, Genetic triangulation coined by Bill Hurst is a method of determining the mitochondrial DNA ancestral haplotype with the help of two or more already known data points. The method of finding a point using two or more known data points has existed for ages and has been used in multiple different fields such as mapping, navigating and certain ambits of social science as well. However, it was not until 2004 when Bill Hurst, a prominent genetic genealogist, coined the term ‘Genetic Triangulation.’
What is Triangulation?
Genetic Triangulation does not necessarily have one particular use, and hence can have varying definitions. One main contention with a uniform definition is the fact that Genetic Triangulation and its usage to understand Y-DNA and mtDNA is different, which makes it a little confusing to follow. It is mainly a process or a method that involves three people or more that have an overlapping segment of DNA in common in their family trees. The reason this is used is to figure out who the shared ancestor may have been. In Genetic Triangulation, the group of three or more people that are being studied to discover the shared ancestor are called the Triangulation Group or TG. The overlapping segment of DNA that these people have in common is known as the Triangulated Segment.
One of the important ways in which Genetic Triangulation is used is to understand and extract as much information out of at DNA tests. If testing involves close relatives, Genetic Triangulation is an excellent tool for working with segments.
Why does Triangulation need to be properly understood?
To eliminate the risk of confusions, the term triangulation needs to be thoroughly understood. It is obvious that geneticists may have slightly varying definitions of Genetic Triangulation. When a Geneticists or Genetic Genealogist hears or reads the word triangulation they a very specific understanding of it. Identifying that a DNA segment is ‘triangulated’ means that it has a unique status as opposed to all other types of genetic data analysis.
It is necessary first to understand what triangulation is before we can be well read enough to ascertain if a segment is actually triangulated or not. Any form of misuse of the term can be very misleading and can also waste someone’s time when they realize later on that triangulation was misused and they have to re-analyze the data. This is especially a huge problem in cases where there is a lack of sufficient evidence to fully determine whether or not DNA segments are triangulated or not.
Triangulation is not just used in the genetic context, which is why it can be really difficult for those who are new to the understanding of genetic triangulation and can easily mix it up with something else. These new people can make problematic deductions from the data because they have failed to understand triangulation or have been lead to believe an incorrect definition of triangulation.
What are the prerequisites?
To conduct Genetic Triangulation, it is necessary for there to be three people. Not just that, it also requires for all three of them to share the same overlapping DNA segment that they have in common with each other. If all three do not have a DNA segment in common, then this process will yield no proper results.
How does it work?
This process is an incredibly systematized and crystallized method of DNA segment analysis which is why it has a few detailed steps. These are as follows:
This part of the process means collecting the match-segments. It is recommended to use different companies as opposed to just one, just in case any discrepancies and human errors occur. Ensure that all of the segments are in a spreadsheet. Make sure that all of the data, even if you choose to opt for one company as opposed to different ones, is being saved and updated regularly. You might need to follow the format of whichever company you are using, but that will not be that big of an issue. The most important point is to avoid errors and to keep things updated.
Segments over 7cM or even 10cM are easier to work with. Smaller sections can be worked in later on.
Since the people in the group may be related, it is possible for them to share multiple different segments. It is important to keep them in separate rows on the sheet. Here is what the sheet should have:
- A column for MatchName
- A column for Chromosome
- A column for SegmentEndLocation
- A column for cMs
- A column for TG
- A column for SNPs
- A column for testee
The next step is to arrange everything in the spreadsheet by Chromosome and Segment Start Location. The column dealing with Chromosome is the first level whereas the other one is the second level. This makes this arrangement sort the data into two levels. The arrangement of the chromosomal data is significant because this ends of sorting your chromosomes from 1 to 23 in order. This just makes it a simpler when the time for putting the overlapping DNA segments close to each other in the sheet comes. It is much easier to compare it when things are arranged properly.
The last step is that of grouping and comparing. The next thing to do after the data has been organized into two levels in the spreadsheet is to start then comparing and grouping overlapping DNA segments together. Comparisons can vary from company to company, but generally, the idea is pretty universal. Two segments are compared, and they either match each other, or they do not match at all. Those that match will form a triangulated group on one particular chromosome. This particular TG is named something. This process is repeated with all other DNA segments that did not match the TG that has just been created, and it is probable that other TGs will be set up with this method.
This leaves you with four categories:
- 1. First TG: The first TG formed with segments that matched
- The other TG: This is done by comparing all other segments that did not match the first TG. None of the segments that are in the second TG should match with the first one at all.
- IBC or IBS: the segments that do not match either of the TGs
- Unknown/Undetermined: The triangulation was incomplete or impossible due to lack of segments or lack of enough overlapping in the data.
A few companies
There are many different companies that help people conduct Genetic Triangulation. Out of the many that are active, some of the most famous ones are:
What do Genetic Genealogy and Genetic Triangulation aim to prove?
Both genetic genealogy and genetic triangulation seek to establish the relationship between individuals regarding their shares ancestors. They intend to look at common DNA segments within the genetic structure of individuals and then use that to trace back to a Most Recent Common Ancestor i.e. MRCA.
This is exceptionally useful for those that wish to understand their genetics and their family trees further, and also want to find answers to certain traits that they have that might not be easily explained. It is also a fantastic tool to study how genetics works and how interrelated people with common DNA segments are.
What tools are used for this process?
As mentioned above, there are several companies that focus on and cater to people that want to understand their family trees and genealogy better. They offer their clients the ability to use Genetic Triangulation to find those that may be related to them. However, not all of the companies that aim to do so actually have the equipment needed to successful conduct Genetic Triangulation.
Companies such as JWorks, KWorks, ADSA at DNAGedcom and GEDmatch’s Matching segment Search, while being companies that aim to do exactly what genetic triangulation does, are not genetic triangulation tools. All they can do is find the matching DNA segments among different individuals and then give them an ICW or In Common With status which is not the same as Triangulation. It is common for ICW groups also to be Triangulation groups, but they are not Triangulation groups. For these to be triangulation groups, all of them would have to have the segment of DNA in common.
A good alternative to such companies for triangulation is the Tier 1 tool that GEDmatch has. It performs triangulation and ensures that the confirmation of a reported group of triangulation sharing the DNA segment is free of all errors.
A True form of triangulation is only possible if you follow all the prerequisites and have segmented data in which an overlapping is seen, and a segment is shared by more than two or two genetic matches.
AncestryDNA and Family Tree DNA are two of the companies that people go to for their genetic makeup analysis and to find out if they have common ancestors. However, genetic triangulation cannot be done at either of those places because they are not completely equipped with the requisite expertise and equipment, at least as of yet. There are reports of 23andMe having a newer Triangulation tool, but it is yet to be properly and thoroughly reviewed and tested. GEDmatch however, has a great triangulation tool which makes it possible to check if two or more matches have a shared overlapping DNA segment in common.