Saturday, November 25, 2017

Basics: Generations Are Calculated Differently at GEDmatch and Viewing Trees

Generations Are Calculated Differently at GEDmatch

This is a screenshot is from my GEDmatch One-to-Many page. 

Gen is an abbreviation for generations

Parents = 1st Gen
Grandparents =2nd Gen
Great-grandparents = 3rd Gen
2nd Great-grandparents =4th Gen
3rd Great-grandparents = 5th Gen
4th Great-grandparents = 6th Gen
5th Great-grandparents = 7th Gen
6th Great-grandparents = 8th Gen
7th Great-grandparents = 9th Gen

When you look under the Gen heading on your One-to-Many page, it is an estimate of the distance to your most recent common ancestor (MRCA) you share with your match. There is a number and GEDmatch puts in a "." followed by a different number to establish degree based on the amount of DNA shared. Siblings are always 1. something. Full siblings are usually 1.2.  I have noticed while working with adoptees if there is a half-sibling this will usually show 1.5. 

I think this "." is to try and pinpoint the once removed, second removed and such. However, DNA is not consistent and one person may show different amounts. So full siblings are 1.2, 1.3. 

The Gen 1 combined with total DNA over 1300 cM indicates siblings who share at least one parent. If you are a female and have a half-sibling who is also a female you will share 196 cM of X and share a biological father. (Sometimes on One-to-Many it will show a tiny bit less.)

Most genealogy sites consider YOU the start point of a tree and thus you are generation one; on GEDmatch your parents are considered GEN 1.

When Viewing Trees

When you click on a GED on your One-to-Many page to view the trees of your matches, you can reset the number of generations to view. I like to set it for several generations beyond what the amount of DNA shared suggests our GEN should be. When I do this I don’t have to click those arrows in a tree to see a surname we might share. I usually set the view to 12. Choose the number of generations you want to view in the pull-down and click Submit.

When working with triangulated groups I copy and paste the trees of those matches (that have them*) into a single document that is set in landscape (under the layout tab) with margins at .3 or 1/3 inch.

(Use Ctrl+A to select everything, then right click copy with your mouse, then when you are on the page left click to paste. You can also use Ctrl+V to paste)

After I paste it on the page-

I select by highlighting (left click your mouse and drag it over what you want to highlight) and reduce the size of the font type in the entire tree to 8. This gets everything on the page and makes it easier to read what you need to. (I usually delete the major page headings on the tree so I only end up with the tree. You can do that by highlighting the part you want to delete and click the delete button on your computer. You can also place your cursor after what you want to delete and click the backspace.)

Using the Gen provided by GEDmatch, I count back to the estimated level of grandparents in the tree (I use my fingers to count), and highlight and enlarge their names in that generation to a font size of 10 and click bold. This makes the surnames stand out.

When all of the trees in the triangulation group are on a single word document it is easy to scroll up and down reading the enlarged bolded surnames and find repeated surnames in the various trees. This makes finding the most recent common ancestor (MRCA) or a common surname stand out.

* This is another reason for having a tree on GEDmatch. If you don't you are missing out when others are searching you in a triangulated group (TG). You are helping them help you by identifying a common ancestor you share on a specific chromosome and letting you know who it is. Then they can email you let you know they have the same couple and where your shared DNA is located. (If you are adopted and know one side of your family tree, upload it to GEDmatch to get more people looking at your tree. You can enter the unknown parent as unknown.)

When you have segment and position information and someone sends you a one-to-one comparison of how they match you, you can give them the names of your known shared MRCA's at that location. Of course, remember there are going to be two, one on your maternal side and one on your paternal side. 

Also, as the distance increases in Gen you are stepping back another generation and if you share a smaller segment in the same area with another TG, you may share a different common ancestor, often in the same line. So, if you have identified your 4th great-grandfather, your newly identified MRCA with a smaller segment may share the 5th or 6th great-grandfather in that same line if the surnames are the same.

Happy Finding! (I'm having a blast!!!) 

Coming soon--I have been blessed teaching classes at different libraries and genealogy societies in my area. They have taught me a lot. One major challenge for many genealogists who want to understand about DNA is they also struggle with basic computer skills. Let's face it, I'm a grandma. I did not grow up in the computer era and struggled to learn. I am convinced when you can overcome that challenge, you will soar. 

I also believe you do not have to fully understand genetic genealogy to be successful finding family and knocking down brick walls. You just need to know which buttons to push on which programs. I am in final edits of a book that will soon be released on Amazon. It is for the DNA and computer challenged. It is geared to the adopted person (or someone who has an adopted person or NPE in their family). 


  1. oh thanks for sharing this article on your blog. My younger sister was in search of this topic for some time. I hope it will help her understanding the gneration trees and differences

  2. Happy that this post might help her.