Gedmatch.com is a volunteer-run free website that allows you to upload your raw autosomal DNA data from AncestryDNA, 23andMe, and FTDNA to use their host of tools. I will start off with the warning that they are so backlogged with new uploads that they aren't accepting any new ones until mid-August (currently the 15th). But I've put off this post for so long, that I think it's best to just let you know about all the features and let you get ready. So what does Gedmatch do that's so special? Why will you be sitting on the edge of your chair waiting for August 15th?
One to Many
The first option for analyzing your data is the "one-to-many". This option allows you to compare your data with the entirety of Gedmatch's database. Now, I'm going to take a moment to mention IBS and IBD. Inherited by Descent (IBD) is the term used when your DNA matches someone else, because you've inherited the DNA via a common ancestor. Inherited by State (IBS) is when your DNA shows a match, but is most likely due to just random jumbling of DNA that looks like someone else's DNA. How do you know if your match is IBS or IBD? General rule of thumb in genetic genealogy: a DNA segment must be at least 7cM (centiMorgans) long in order to be IBD. Now, 7 cM is terribly small. To put it into perspective: a sibling will have 2350cM in common with you. A 1st cousin will have 800 cM, 2nd 200....by 5th cousins, there's only 25cM in common! So a segment match of 7 is going to be way back there. If you're looking for close relations, you'll want to look at larger segments.
Why is that all important? When you go to the "one-to-many" tab, you'll be asked what you want the minimum length of autosomal DNA segments to be for your matches. It's default setting is 7cM. Go no lower. A second length option you have to set is for the X chromosome. Now, there is value in an X chromosome match. If you match a male on his X chromosome, then your focus should be the maternal side of his tree. The default value for the X is 3cM, however. This tool will pull up any matches of autosomal DNA of 7cM OR 3cM on the X chromosome. So you could end up looking at a lot of matches that are high on the X chromosome, but below the threshold on the autosomal DNA. Does that mean you aren't related to them? Not entirely. The problem is that the X chromosome isn't gender specific. Yes a male has only one X and gets it from his mother, but his mother got one from her father as well as her mother. So the variety of ancestry makes the X unreliable on it's own (for right now). When you set up your defaults, set the X option higher (30 or more) to filter out any matches below the autosomal threshold. You can always look at those matches later, but your first foray will be less confusing if you leave those bits off. There is also a check box for cross referencing. I won't get into what it is, because it's unreliable. Just don't check that box.
|This is the one to one of my best match and myself.|
I would focus on the chromosome 2 segment as it
meets the 7 & 700 rule.
One to One, X One to One, Phasing, One or Both, and Specific Segment
The next options on the home screen are "one-to-one" and "X one-to-one" comparisons. These are similar to the results you get when you click those "A" or "X" links on the "one-to-many" results, but you can better control the minimums to fine tune the comparison. To be honest, the only time I use these is when someone in a discussion group tells me their kit number and I check to see if we are matched. Same rules apply: 7 & 700. "One or Both" is the option if you want to find matches for more than one kit. When I finally am able to upload my cousin's raw data, this option will help me find the kits that match us both much quicker than running separate reports and comparing names myself.
Phasing is an option I haven't explored as I'm not a parent, nor has either of my parents taken the test. What phasing does is take one or both parents' kits and compare them to their child's kit to figure out what DNA is mom's and what is dad's. It takes a while for the results to come back (about 3-5 days).
And then there is the "Specific Segment" option. You can put in the chromosome number and the segment start and end points, with the thresholds for minimum length allowed, and a report of kits matching you specifically on that segment come up. I've tried it with the chromosome segments that my closest matches have in common with me, but haven't found anyone with a significant match on that segment other than them. Ah well.
Admixture is the fancy name for ethnicity. When you took your autosomal test, the company you chose used their own reference populations and algorithms to calculate your possible ethnicity mix. Now, as I've pointed out before, there's a lot of guess work involved. Let me illustrate the point for you:
I used the K12 for each (save Harappa) to give a fair comparison. That means there were 12 possible categories to have represented in my DNA. Every calculator save Harappa has multiple options as far as how refined the results will be. Eurogenes will go up to 36 categories. Well that means we'll get better results, right? Not really. At some point, you can take your DNA to such a small amount that what you match isn't really proving your deep ancestry as much as reporting noise. Just like the matching needs to follow the 7&7 rule, ethnicity works best at 5% and above. Most people, including the developers of these tools, will tell you that K12 is your fairest bet.
1. I've started a discussion group on Facebook for those looking to compare notes and ask questions:
Gedmatch. Discussion Group. Even though Gedmatch is in the title, we'll discuss anything related to genetic genealogy. We've got some files and explanations already up, but no question is discouraged.
3. This is a volunteer site. They don't charge a membership fee. When AncestryDNA finally allowed raw results to be downloaded, this site crashed twice from the number of people uploading their results. Now it's backlogged and runs the risk of crashing again when it allows new uploads. PLEASE take a moment to donate to the site via Paypal or the snail mail address listed on the site. You don't have to pay, but it's the right thing to do. This site makes using third party genetic tools easier for everyone. They give you a place to compare your DNA to people who took tests from other companies. They ask for nothing. They deserve support. Your money makes sure they can keep the site running and buy the server space necessary to give you as many matches as possible. Our continued support will mean improvements to the site as well! Even if all you can give is a little, give it. Give it twice. When you have a little extra cash and think about all those wonderful new matches you've discovered, give that money to show how grateful you are for this opportunity. Encourage others to give. Donate now so they aren't forced to make it a paid site to keep the lights on! (Don't think it can't happen).