I Have My DNA Results. Now What?

"I understand cMs, but I have no clue when it comes to segments. I also can see where I match on Chromosomes, but I don't know what use I can make of it."

Submitted by VCB to the "Raise Your Hand!" section of DNAClassroom.com

This is a question that is faced by all new researchers. Because each testing site has different tools and techniques you can use to make the best use of your results, the specific steps for getting started will differ depending on the DNA company where you tested, but usually involves using those company tools to explore your matches. In this Lesson Blog, we’ll provide the basics of what you can do to begin the process of working with your DNA and to make valuable connections with your matches, no matter where you tested. Despite company differences, there is basic information that applies across testing platforms. The first involves centiMorgans (cMs). In the simplest of terms, genetic genealogists use cMs to measure genetic distance in DNA testing. Ancestry, FTDNA, and MyHeritage quote their matches in cMs, whereas 23andMe uses percentage of DNA share. The amount of DNA shared between two individuals holds clues to help estimate the relationship, at least to the 3rd cousin level. For a more detailed explanation of centiMorgans, please see Using centiMorgans to Estimate Relationships

Once you understand how centiMorgans help identify potential relationships, the next step is to make the best use of your results. At 23andMe, FTDNA, and MyHeritage, you have access to segment data, or the ability to visualize the location of a match on a chromosome. When two individuals are said to “match” it is because they share segments of DNA that were passed down by a common ancestor or ancestors. This is where the magic of DNA research comes into play. The goal is to identify the source of that DNA by comparing trees with individuals who match. There are two ways to do this, Triangulation, and exploration of Clusters of matches. Let’s define these two terms. Triangulation is the process of identifying three or more people who share the same segment, then comparing trees to try to identify a common ancestor shared among the group. Shown in the following example, are 3 matches to the same cousin, all sharing the same ancestral pair. Note the overlapping segments on chromosome 19 with their cousin. Although the start and endpoints are different to their cousin, there are overlapping sections.

However, in this scenario, it’s important to compare each to the other to eliminate the possibility that the individuals might happen to share a common segment location with you, but one is a maternal match to you while the other is a paternal match to you. To do so, you need to compare A to B, B to C, and A to C to confirm the match.

This is most easily done at 23andMe, or at the free sharing site, GEDmatch, which accepts uploads of raw DNA data from various testing companies. MyHeritage does show a Triangulation symbol, which will allow you to see how various matches share a segment with you and another person. You’ll be able to see that all match you on the same segment, but will not be able to see how they match one another, which may be a greater or smaller share than each shares with you. Otherwise, you’ll need to contact your matches and have them confirm the location of the matches on their end. Let's see how this works with the same example of the 4 cousins sharing the same ancestral pair and matching on Chromosome 19. As it turns out, while Matches #1 and #2 do indeed match each other and share the same segment to their cousin, match #3 does not match the other two and is, in fact, a maternal match to the primary tester whereas the others are all paternal. In this case, the mother of the primary tester has also tested her DNA, allowing us to use MyHeritage's Triangulation feature to see how Match #3 triangulates between the tester and her mother.

In this example, while Matches #1, #2, and #3 can point to sharing a segment location and an ancestral pair with the original tester, only the original tester, Match #1, and Match #2 would be said to Triangulate. Match #3 would need to be explored further for the origins of the maternal DNA shared with the original tester. For more on this exploration, please see Not so Fast! When a DNA Match Isn't What It Appears To Be. Unlike Triangulation, Clustering does not require that the entire group share the same DNA segment. In this scenario, some of the matches will triangulate with one another, while others in the cluster will match you or others in the group on different segments. Those, in turn, may triangulate with others within the clustering group.

To explore how this might happen, keep in mind that, in most cases, we’re not dealing with just a single ancestor, but with an ancestral pair. If, for example, a group of people share the same 4th great grandparents, DNA can be passed down from both the 4th great grandfather and the 4th great grandmother. Some in the cluster will have inherited DNA from both, while some may have only received DNA from one of them. In this simplest explanation, those who match both would tie together the entire cluster. In reality, it’s typically more complicated than that because each of those 4th great grandparents had DNA from each of their parents to pass down to their offspring, creating the likelihood that there are multiple segments to be considered among the cluster. For more on Inheritance patterns, please see Two Peas in a (family) Pod. The following example shows the potential origin of a cluster, Cousin B compared to three 3rd cousins who are siblings of one another. By using the GEDmatch Genesis, Compact Segment Mapper, we can see how Cousin B shares segments with each of these siblings.

As you can see, Sibling S shares 5 segments with Cousin B on Chromosomes 2, 3, 13, 13, and 16. Sibling T shares 2 segments with cousin B, including the segment on Chromosome 3 that is shared with Sibling S and a segment on Chromosome 10 that is not shared with the other siblings. Sibling L also shares 2 segments with Cousin B, including the second segment on Chromosome 13 and the chromosome 16 segment, both of which are shared with Sibling S. Because Siblings T and L do not share any of the same segments with Cousin B., their descendants will never Triangulate with descendants of Cousin B. However, should their descendants inherit some of this shared DNA, they could well Cluster because of the segments each shares with Cousin B and Sibling S. Of course, this is the simplest of explanations. In reality, there would be more data included with other cousins contributing additional DNA not represented in this one scenario. While we have manually shown you the origins of a cluster, there easier ways to visualize a cluster that has been expanded to include other cousins. The good thing about working with clusters is that there are now a number of automatic clustering tools available. In addition to third party sites such as Genetic Affairs, DNAgedcom Client, and GEDmatch Tier 1 Clusters, MyHeritage has a built in clustering tool.

In this MyHeritage Autoclusters tool, the names of the matches are listed at the top and sides. A colored dot is placed where the two matches share DNA and no dot shown when they do not share DNA. Every match in a cluster is a match to others within the cluster, but not necessarily every person. Distinct clusters have been assigned a separate color. Your task is to examine each cluster and try to determine what links each group together Putting Triangulation and Clustering to work At this point in time, receiving your DNA results will not simply hand you your entire family tree. Working with your DNA takes time and organization. For greater success: 1. Take good notes, especially when you find groups of matches who share common surnames that you’ve not yet identified in your tree. As new cousins test, the resulting additional evidence may well clarify previous match groups that weren’t clear initially. If your results contain a lot of notes, you'll save time and effort each time a new match comes in. 2. Look for patterns. Patterns can include surnames and locations that may well lead to records to help clarify how these groups are related. One discovery may well lead to others. 3. Build trees if your match's tree does not extend to a generation that is suggested by the amount of shared centiMorgans. Be sure to include any clarifications in your notes. 4. If you feel that you've established a Triangulation Group, consider using the segment mapping tools at DNA Painter, labeling the segment by the common ancestor/s shared with each match. 5. And, as we often say here at DNA Classroom, work collaboratively with your matches. Together you can accomplish much more than you can do on your own. Give it a try! Source Citations: 1. Images: MyHeritage DNA. Image Capture, Chromosome 19, various. [cited 2019 Aug 13]; https://www.myheritage.com 2. Image: GEDmatch Genesis - Compact Segment Mapper. [cited 2019 Aug 13]; https://www.gedmatch.com 3. Image: MyHeritage DNA Autoclusters [cited 2019 Mar 15]; https://www.myheritage.com #DNA #Genealogy #Triangulation #Clustering #understandingDNAresults