Getting Started With GEDmatch
UPDATE: This tutorial applies to GEDmatch as it was a few years ago. You will find that some screens have altered but I have left this tutorial online as it may still be of some help.
At first glance, GEDmatch can seem a bit daunting but actually, once you become familiar with some of the tools and try them a few times, it's fairly straight-forward. This 'Getting Started' tutorial will show you how to use the right GEDmatch tools to help you to work with your DNA matches.
What is GEDmatch? It's a free service where you can upload your raw DNA data file with the potential of matching with more cousins than just the ones you see at your testing company. The site also provides some useful analysis tools, not necessarily available at your testing company, and other utilities such as Admixture (ethnicity) tools.
First you need to register for an account at GEDmatch
and the next step is to upload your DNA file from your testing company.
You will need to wait a few hours or a day or so for your kit to finish processing and then the One-to-Many tool will become available.
The One-to-Many Matches Tool
Begin by choosing the 'One-to-Many' matches tool in your Dashboard.
Some of the Analysis Tools at GEDmatch
Enter your kit number. You should be able to use the drop-down list to access your kit number. Don't change any of the other options, then click on the 'Display Results' button.
The One-to-Many Lookup Tool at GEDmatch
Personal details have been obscured for privacy
On the next page you will see a list of your top 2000 nearest DNA matches. Choose someone in the list that you want to compare with and then click on the 'A' link in the row of your chosen match. People often begin with their higher unknown matches.
The beginning of my list of One-To-Many Matches at GEDmatch
The One-to-One Comparison Tool
You should now find yourself on the One-to-One comparison page which incidentally can also be accessed directly from the Dashboard. Carry out a One-to-One comparison with the 'Graphics and Position' option selected. Leave all the other fields as they are. After pressing the 'Submit' button, you will be presented with a graphical display of each of the 22 pairs of autosomal chromosomes where you match (or not) the other person.
A GEDmatch One-to-One Comparison between me and my 1st cousin once removed
The screenshot below shows where I match my first cousin once removed on chromosome 5. (There isn't anything special about chromosome 5. I've just chosen it at random.) The blue sections are segments of DNA where we match each other. As you can see, we happen to have two matching segments on this particular chromosome.
Chromosome 5 from a One-to-One Comparison between me and my 1st cousin once removed
Base Pairs
You will notice there are start and end locations. This is a measurement in base pairs and shows exactly at what point along the chromosome the match is - in our case it is 28.5 centimorgans (cMs) between the start location of 108.5 million base pairs (Mbps) and the end location of 141.3 Mbps and also 20.8 cMs between 161.4 and 172.2 Mbps.
Centimorgans
The centimorgans figure informs us of the quality of the match, the higher the total number, the closer the match. A full parent/child match is something in the region of 3600 centimorgans and it drops quite quickly the further apart the relationship is. Any segements below 7 centimorgans are dubious. This is because it's possible to have segments which are known as IBC (Identical by Chance). In other words, they are false matches. This is why you don't want to use anything below 7 centimorgans but segments above this figure aren't necessarily genuine either which is why many people prefer to work with a higher threshold. The opposite is called IBD (Identical by Descent) which means a genuine match. As a general rule, about 90% of 3rd cousins will match each other, 50% of 4th cousins will match and only 10% of 5th cousins will match each other. However, it is still possible to match more distant relatives due to the randomness of DNA inheritance.
GEDmatch One-to-One Comparison Results
At the foot of the One-to-One results page you will see something like the above screenshot. Take note of the total number of centimorgans. In my case, I share a total of 357.7 cMs with my 1st cousin once removed. MRCA means Most Recent Common Ancestor and the estimate of 2.7 in this example is in the right area. I happen to be 3 generations away from our MRCA and my cousin is two generations away. Bear in mind that the MRCA figure is just an estimate and can be less reliable when the relationship is more distant. For many of your cousin matches you will match on just 1 or 2 segments of DNA and share a much smaller total number of centimorgans. There are several charts available to calculate the relationship based on shared centimorgans. One of my favourite charts is by Blaine Bettinger whose website is at thegeneticgenealogist.com and an interactive version of this chart has been made available by Jonny Perl HERE.
Working with your DNA Matches and Triangulation
It's important to realise the graphic of chromosome 5 above is a representation of both the paternal and maternal chromosome 5. From this, it's not possible to identify which side a previously unknown match is on until you begin to look at your match's tree and compare. If you have parents tested then you can narrow down which side of the family the match is on straight away. For instance, if your mother also matches the other person on the same segment then you know the match is maternal. Because this is a close cousin of mine, I already know how we are related. Nevertheless, my cousin's DNA is extremely useful to me because, if she matches someone else on the same segment as my mum and/or aunt, then I know I need to be looking at my maternal grandfather's lineage because that is how we are related to my cousin.
In an ideal world you would hope to find three or more people who all match each other on the same segment. This is called triangulation and indicates that each person is descended from the same ancestor or ancestral couple (MRCA) or maybe one person is descended from an older ancestor in the same line. It is vital that everyone you are comparing matches everyone else at least 7 centimorgans or more by carrying out one-to-one comparisons BETWEEN EVERYONE in the group.
For example:
A must match B.
A must match C.
B must match C.
(Note: if B does NOT match C then it could be that A is matching B on their maternal side and A is matching C on their paternal side, for example.)
The three matching people need to descend from the ancestor on different lines of descent to count as a separate leg of the triangle. For example, my mum and I would only count as one leg of the triangle. In the case of my first cousin once removed, our common ancestors are my great-grandparents, James Geake and Sarah May Hellyer. I descend through their son, William (Bill), and my cousin descends through their son, Ronald (Ron). This would count as two separate legs descending from my great-grandparents. If we were tracing a number of generations further back, then it could be argued that our close relationship with our cousin might actually be more representative of one leg of the triangle.
You may have a number of matches to other people but finding a third person to make up the triangle may not be so easy. Triangulation isn't always possible when you consider that different segments from a given ancestor, rather than the same segment(s), might pass down to different people. Therefore, discovering people with the same ancestors in their tree but who do not all match on the same segment but all match each other on different segments (known as 'In Common With') COULD be an indicator that you are indeed all related through that same ancestor but it is by no means guaranteed.
The 'People who match one or both of 2 kits' Tool
So how do you find others who match you and another person? In the GEDmatch Dashboard, choose the 'People who match one or both of 2 kits' option and put your kit number in the first box and the kit number of your chosen match in the second box. The default levels are set at 10 cMs. If you don't have many matches you can drop the thresholds from 10 cMs to no less than 7 cMs.
The 'People who match one or both of 2 kits' tool at GEDmatch
On the next page, the top section provides you with a list of kits who match both of you. You can select some or all of these kits by placing a tick in the box next to the email address and clicking the 'Submit' button near the top of the page.
A list of GEDmatch kits which my 1st cousin once removed and I both share
After this, choose the button for the 2-D Chromosome Browser and then click 'HERE' on the following page.
The 2-D Chromosome Browser
You will now see a graphical comparison of where everyone you selected is related to YOU (as long as you put your kit number in the first box at the 'People who match one or both of 2 kits' stage). You won't see yourself in the display because yours is the master kit and everyone in the display is shown in relation to you. In my example, my 1st cousin once removed shares over 86 cMs with me on Chromosome 18. She is represented by the orange line (Match ID 1) in the screenshot below.
The GEDmatch 2-D Chromosome Browser
Match ID 2 in the graphic above lines up with me and my known cousin on a smaller segment (almost 26 cMs) and will probably be related further back in time so long as they triangulate. Match IDs 3 and 4 share even smaller segments with me and may be related further back again.
I have carried out One-to-One comparisons between all of the above kits and everyone matches each other so they do triangulate. However if, for example, Match ID 4 did not match my known cousin and the others, then this would indicate they were a match on my father's side instead (because I know my relationship with my known cousin is maternal). As stated beforehand, you cannot tell whether they all match each other just because the segments line up. You have to compare everyone with everyone else.
Be careful to look at the number of cMs when viewing segments in the chromosome browser as the graphics often include segments smaller than 7 cMs as well as larger. There is a legend at the top of the results page to help you identify the size of the segment by colour. Discard all pink segments and be careful with the blue ones as these range from 5 to 10 cMs.
Legend for the 2-D Chromosome Browser
GEDmatch User Lookup
The next step is to see if your matches have family trees. Go back to the Dashboard and choose the 'User Lookup' link on the left side of the page to find out whether the other matches have uploaded a GEDCOM file (family tree) to GEDmatch. Many people omit to do this but I highly recommend you upload your own GEDCOM file after uploading your DNA file so you can help those who match you.
GEDmatch User Lookup Link
On the next page, put in the kit number of the match and click the 'Display Results' button. If your search doesn't reveal a GEDCOM file, take note of the email address. Then go back and delete the kit number and enter the email address instead. Sometimes people forget to attach their DNA kits to their GEDCOM files. By using the email address it also provides a handy way to find out which other kits the person has registered under their account.
GEDmatch User Lookup Results
If there is a GEDCOM file, click the link beside GEDCOM ID# and you should arrive on a page belonging to the DNA match if they've attached their DNA correctly. The 'Pedigree' link near the top of the page will take you to a chart of the person's ancestors where you can look for familiar surnames or place names to help you identify how you are related to your match.
My GEDCOM file on GEDmatch
In addition to the User Lookup, you can also see which of your matches have GEDCOMs by means of the GED or Wiki links on the One-to-Many results page (see the List of One-To-Many Matches image above).
If there's no GEDCOM then try Googling the email address of your match to see if you can find a tree or perhaps search for the person on Facebook, etc. where they might mention their research. Some people put a tree on Ancestry even when they haven't tested with them. Finally, there's the option to email the match to ask for more information.
It's worth mentioning there's a GEDmatch tool which will provide all of your top 500 triangulations for you without having to manually do the One-to-One comparisons. If you wish to use it, you need to make a donation to GEDmatch for Tier 1 tools.
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