Wednesday, May 31, 2017

Tier 1 Gedmatch Matching Segment Search

The tool “Matching Segment Search” on Tier 1 tools loses some of its visual clarity during the process of copying and pasting into a spreadsheet. You get a better visual understanding by being a Tier 1 member. The developers have done a great job to compensate by using color coding to help identify possible match groups on each chromosome.
When the color on the column changes, it indicates a different group of matches who potentially  share a different common ancestor. (This is due to something called recombination. You can learn more about recombination HERE.
This workbook sheet presents matches in order, beginning with chromosome 1 through chromosome 22.

When viewing on the Gedmatch website you see a variation in size of the shared segment on a chromosome. Below, everyone listed in the purple group, match on at least some of the same position on the same chromosome. This visual shows some people share more of this segment with you than others. The worksheet  includes the segment size that is shared. Though not an actual triangulated group, those who show the same color indicate they hold the potential to be a triangulated group.

The picture below is what you see in your copied and pasted workbook spreadsheet. Instead of the narrower and wider graphic, a  big block of the same color indicates you share at least part of common area on this chromosome with everyone else listed with that same color; and thus, the same common ancestor. (There are times you could share this same color simply by accident.) That is why it is important to discover your common ancestor with people who share segments over 15 cM first. (Email them to compare trees.)
The header on Matching Segment Search titles all the pertinent contact information, and the segment start and end location and the size of the segment you share.
As you study your Matching Segment Search page you will also notice a change in the color in the Segments column when you begin a new chromosome.
If you share on more than one chromosome with a match, don't assume the match is for the same common ancestor. It could indicate a different common ancestor. For instance one match may be for a common grandfather, the other match could be for a common grandmother. Or, it might even be for the parent of a common grandparent. You will have to find out who others in the triangulated group share by studying their genealogical trees.
(If you have an adopted person in your group, you can greatly assist them by notifying them of the common ancestor they share with you and others in the group.)

When studying segments think of a triangulated group as you would a three legged table. The table top is the common ancestor; the legs represent descendant lines through three different children.

Let’s use Hugh Brady b. 1709 as an example. I discovered I match with a descendant from his daughter, Mary; and a descendant from his son, Ebenezer on the same chromosome and segment. Together we are a triangulated group. Our most recent common ancestor (MRCA) is Hugh Brady. Hugh is our common link. Everyone else who shares this same segment/color grouping on the same chromosome should also  have this same Hugh Brady in their tree. This segment of DNA can be identified, Hugh Brady b. 1709.
If your testing company is AncestryDNA, you may have noticed there are times when your ancestor hint you share with a match provides more than one ancestor with whom you share your DNA. This could be because someone doesn't have their tree filled in correctly. OR, it could mean you need a third person to triangulate with, to determine who your common ancestor actually is. There has to be at least 3 people, not too closely related to have a triangulated group.
On the Matching Segment Search you can have more than three people in your triangulated group (same color, same chromosome, share somewhere on the same segment) and their genealogical trees should all include the same common ancestor.
Email them to find out who it is.
Hint: To more quickly identify your shared segments to a specific surname in your tree; do a surname search on your testing company's matches page. Try to find descendants from different lines where you have a common set of ggg (or more distant) grandparents. Use matches beyond second cousin range. Get their Gedmatch Kit Number. Do a one-to-one match on Gedmatch and identify the chromosome where they match you. Find them on your Matching Segment Search page.  Email the other people who are in the same color group. Check their tree and confirm the same common ancestor. Insert a column in your spreadsheet and write the name of your common ancestor for this color group. Now, when a new match appears, and matches you in the same location, you instantly know who your CA is  by looking on your Matching Segment Search page.

Happy Finding!


  1. Thanks for doing these great descriptive about the bar charts and the Tier 1 segment matching. Now that there is an option to select a chromosome at a time on GEDmatch, it makes it easier to digest!

  2. Barbara, just wanted to pop in again and thank you for these great DNA articles! You writing clarified so many questions I had. Love the "image" of the three-legged table for triangulation (-: p.s. I think you are on WikiTree? I am a leader there, under "Maggie N."

    1. Yes, I am. I do blunder around and love WikiTree. I found you but no link to your profile:(. I need to take some training from one of my friends. I convinced her to upload and use WikiTree and she won some sort of prize for sourcing. She's going to have to teach me now!

  3. I only discovered that YESTERDAY! I plan on doing a very short blog to point it out. Is that awesome? It EVEN DOES 23!!!