Autosomal DNA Matching 101

A friend who is just embarking on the genealogical DNA journey says it's too complicated. I have to agree that it can be overwhelming.

• If you are taking the AncestryDNA test, focus on learning about autosomal DNA. 
• If you are taking the Family Finder test at FamilyTreeDNA, it is also an autosomal DNA test.
• Ignore Y-DNA and mTDNA for now.

The first thing that I suggest is to subscribe to the DNAeXplained blog by Roberta J Estes. Sometimes her posts pertain, sometimes they don't, but her work is a great resource.

After you subscribe to the blog, visit the publications section of Roberta's DNAeXplain.com website. Scroll down to the section titled Working with DNA and see what you might want to download and read.

You've ordered an autosomal test, but what will it do for you? The purpose of an autosomal DNA test is matching your DNA to that of cousins known and unknown. It can answer:

1. Who shares my DNA? 
2. How much DNA do we share? 
3. What segments do we share? 
4. Who else shares those segments? 

Unfortunately Ancestry only answers question 1 and hints at question 2. However, the genealogical community uses Ancestry more heavily than FamilyTreeDNA , so that's where more matching will take place. The Family Finder test at FTDNA answers all 4 questions. The free website GEDMatch also answers all 4 questions.

When your test is completed, you can download your results from Ancestry, FTDNA or 23AndMe, which I don't use. You really don't want to look at your results file -- it's big and has a lot of numbers and letters. But it's yours and you will want to get that download file to use at other websites now and in the future.

What can you do with your downloaded file?

• GEDMatch levels the playing field for matching. It is a free site supported by donations and we who use it need to donate. Bear that potential cost in mind, as well as the possibility the site could vanish.
• An Ancestry test result can be uploaded to GEDMatch.
• GEDMatch accepts uploads from FTDNA.
• GEDMatch accepts uploads from 23AndMe.
• FTDNA accept uploads from Ancestry. It's $69 today to upload.
• FTDNA accepts uploads from 23AndMe, also $69 today.
• Ancestry will not accept an outside test result. 
• DNAGedcom will  accept uploads from FTDNA and from 23AndMe. More on this tool next time.

GEDMatch is the free site where we all can meet, regardless of the original test company. I've chosen Ancestry for my brother's autosomal DNA test, knowing it gives me flexibility in handling the results.

I'll use my cousin Mary as an example of matching via Ancestry and GEDMatch. She and I both tested at Ancestry, which predicted that we were in the range of 4th cousin to 6th cousin with a 96% confidence factor. We also have a leaf that we have a common ancestor in our trees. We had already connected, so none of this was a surprise.

We both uploaded our Ancestry results to GEDMatch.

GEDMatch provides a list of matches, similar to Ancestry. It also includes matches who have tested with other companies.

I look in my match list for Mary (in yellow), make a note of her kit number, and click on a link to run a one-to-one match. The match process provides a very clear answer to how much DNA we share and what the segments are.

GEDMatch estimates 4.2 generations to our Most Recent Common Ancestor. Mary is my 3rd cousin, once removed. Our common ancestors, William and his wife, are 4 generations from her and 5 generations from me. Both Ancestry and GEDMatch have done well with their estimates.

GEDMatch gives us other tools, including the ability to see others who match both of us. Someone who matches us both on chromosome 2 between 74188298 and 105591639 is now known to be related to us in the lines of William or his wife or both. As we accumulate matches, we can refine our knowledge. There can be a "gotcha" here, which I'll cover next time.

As I write this post, GEDMatch is in the midst of a transition with many tools unavailable and new uploads not being accepted. I have every confidence that they will be back to provide for Ancestry users the missing tools.

FTDNA works in similar ways to GEDmatch, but the interface is prettier and comes at a price. Here we see a couple of my Dad's matches.

The top is his confirmed cousin from Sweden. The little green icon shows that there is a family tree (GEDCOM) loaded by that person. The estimated 2nd-4th cousin has been replaced by the actual relationship that we calculated and then manually set.

The bottom match has no tree, but has listed some of her surnames. I'd rather see a tree. That's so important to facilitate making the connection.

FTDNA provides graphical comparison of matches and allows me to download my matches, their email addresses and the chromosome matching segments, similar to those shown above. It also provides a tool to see who else matches both me and one or more of my matches. One of the downsides of FTDNA is that a lot of the participants have not provided a family tree.

The autosomal DNA test is another tool in your genealogical toolbox. You still have to figure out the connections.

I hope this post helps with some basic understanding. Next time: the magic of DNAGedcom.