Gedmatch Basics, Part 1 | Jennealogie

This is one of my top all-time posts, so I have updated it now that Gedmatch has undergone changes. While Gedmatch has undergone a bit of a facelift, the same tools are available, so read on an learn how to use them!

You might be here because you read my last post Please Upload Your DNA Results To Gedmatch and you want to learn more. Maybe you’re new to the genetic genealogy world, and you’ve uploaded your results to Gedmatch but you don’t know what to do next. Maybe you’ve fooled around with Gedmatch for awhile, but you don’t feel like you really understand it. Whatever the reason you are here, welcome. I hope you find this post useful.

First things first. The most important thing is your kit number. That is the number that you will compare to other people’s numbers. You will have to enter it pretty much everywhere on Gedmatch, so you should probably mark it down somewhere where you can easily access it. Beats having to go back and forth from the page where to need to enter it in to the main page.

Once upon a time, the letter in the kit number was significant, but now they are randomly supplied. The letter represents what the original testing company was on older uploads, but now you can easily find that info elsewhere. If you also have an account with that testing company, you might be able to find the owner of that test there. They may have information on that site that isn’t on this one. The old kits were given the following letters: A = Ancestry, T = FamilyTreeDNA, H=MyHeritage, M= MyHeritage 23&Me (thanks for the correction, reader!). 

You can find your kit number under “Your DNA Resources.” You can click the pencil to edit the details of your kit such as the status, name, alias, and to change law enforcement access. The police symbol denotes whether you are opted in. If it has a big X, you are not opted in.

I will quickly explain opting in here, but if you want to know my thoughts on the matter I have written about it more here.

Opt in: Your kit is compared to other kits in the database, including kits submitted by law enforcement. 

Opt Out: Your kit will be compared to other kits in the database, including kits of unidentified human remains (which may have been submitted by law enforcement) but not kits submitted by law enforcement to identify perpetrators of violent crimes.

Private: Your kit is not available for matching to other kits in the database.

Research: Your kit is available to be compared to other kits, but you won’t show up in their match list.

Next, let’s look at other things you can do on this site. To keep this tutorial simple, we’re going to focus on the free tools you can use to analyze your data, specifically tools to analyze your DNA raw data, and more specifically, the tools that are the most useful to a beginner.

1) ‘One-to-many’ matches

This will allow you to see all the matches you have on Gedmatch. These are people who share DNA with you.

Enter a kit number, then click submit. Don’t change any of the settings. Your list will populate below. Let’s go across the top of the table and learn what each column is for.

The first column Select, lets you select a bunch of kits for comparison. I’ll talk more about comparisons between kits in another post. Then you have a match number. Next is the match’s kit number. If you click on it, it will take you to that person’s one-to-many list (maybe you have matches in common). Name/alias is pretty obvious, just note that aliases (nicknames) are prefaced with an asterisk *. Names can be helpful but of course married names obscure maiden ones. Aliases are not as useful, but sometimes if someone is particularly proud of their heritage it might give you a hint. The email can also sometimes give you a hint. Here is my post about crafting an email to DNA matches. A link will show up in the GED/WikiTree column if your match has uploaded a family tree. You can have a look and see if it gives you any indication of how the two of you might be related (I’ll talk about how you can upload your family tree in a future post). Age (days) is how long the kit has been on Gedmatch. It turns green when you have a newer match. Type is what kind of chip was used in testing, not really relevant for our purposes. Sex is pretty obvious. Haplogroup is advanced for our purposes.

Autosomal is the type of DNA we are looking at. It has three columns. Total cM and Largest  require that you know that a cM is a unit of measurement for DNA, short for centimorgans. The total is the total of all the segments you share in common. Largest is the size of the biggest segment you have in common. Generally speaking, the higher the total, the closer you are related to someone. If you enter the total amount of cMs here, it will give you ideas of what relationships to this person are possible. It’s a fuzzy science, though, because the amount of shared cMs people in a given relationship can have can vary, and varies more as the genetic distance increases. For example, between a great-aunt and great-niece, the two people can have anywhere from 251-2108 cMs in common. Gedmatch also gives you an estimate of how many generations you are from this person in the Gen column. If you click on the link in the Largest column, it will open up the ‘one-to-one’ compare page. We’ll talk more about that in a second.

X-DNA is an advanced topic for another day. Source is the company where the person originally tested and uploaded from. Overlap you don’t have to worry about, unless it’s pink. It shouldn’t be pink until you get down to your tiny matches, and working with tiny matches is an advanced topic. You have my sympathies if all you have is tiny matches.

2) ‘One-to-one’ compare

It is always a good idea to run a ‘One-to-one’ compare with a match before you email them. You can click on ‘One-to-one’ compare from the main page, or, if you have run a ‘One-to-many’ matches, by clicking on the link in the Largest column of the autosomal DNA columns. Regardless of how you get there, the ‘One-to-one’ compare page has a spot for two kit numbers to go. If you got to this page by clicking on the link in Largest, the kit numbers are already there.

You have a choice if you want to see both the graphics and position, or one or the other. You can also choose just to see the chromosomes that have matching segments. Once you hit submit, you get to a page that looks like this:

We measure autosomal DNA by counting the number of SNPs (pronounced snips) in common. SNPs are the letters that make up our DNA, more specifically, where our DNA can differ from one person to the next. The more SNPs we have in common, the more closely we are related to someone. The colours that are important here are green, yellow, blue and black. You can see in this picture we have spots that are yellow because we have a half match. Most of our matches are going to be half matches, since a full match (green) means we share the same SNPs on both chromosomes (we have one from mom and one from dad), and this occurs most often with siblings. The blue means the SNP density is good. Think of it like a rating system. You can have 1 review with 5 stars, or 457 reviews with 4.5 stars. The density of the reviews helps us know we’ve got a good product.

My match and I have only one segment greater than 7cMs, and that segment measures 12.9 cMs. I can see from the table that we share a spot on chromosome 2. The start and end location is the address of the segment, and anyone else who shares a segment with both of us at that address on that chromosome is likely related to us through an ancestor we all share. There is no table for chromosome 3, because as you can see from the picture, we do not have any segments in common on chromosome 3.

The last bit of useful information is the largest segment. The total half-match gives us the total amount of DNA we share. Estimated number of generations to Most Recent Common Ancestor (MRCA). This is the ancestor you both have that gave you both that segment of DNA. For siblings, it’s your parents. For cousins, it’s your grandparents. Siblings also have grandparents in common, but parents are more recent, i.e. more closely related to them. It also tells you how many SNPs were used for comparison. 

Here’s what it looks like when you’re not related:

Please note that because testing companies differ in how they do things, one company might mark you and a match as related and another company might mark you and that same match as unrelated.

3) Admixture (heritage)

This is the only section that (sadly) didn’t require an update. Every testing company offers its own version of ethnicity estimates; Gedmatch has several. I’m not going to say anything here but provide a link to a site that explains it far better than I ever can. I would love it if we could get updated admixture, but until we do, you’re better off using the ethnicity estimate where you originally tested.

Please fool around on the site and get used to it. Experiment with different settings. Or not. See if they can get your eye colour correct (please bring this back, Gedmatch!). Check if your parents are related. Then go read Gedmatch Basics, Part 2.

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