Monday, June 13, 2011

Anticipating DNA Results

So you send your sample in for testing and then you wonder what kind of results you might get.  Everyone knows that we inherit half of our DNA from our mother and half from our father.  Knowing this, it is logical that 25% of our DNA would come from each of our four grandparents.  The waters get a little muddier with siblings, aunts, uncles and cousins.  I found this great graphic on Wikipedia that helps make it clear. (All graphics can be enlarged by clicking on them).

Graphic Credit: Dimario, Wikipedia Commons
The Human Genome Project determined that humans share 99.9% of their DNA in common, although this exact percentage has recently been challenged.  This means that all of the diversity among humans comprises a relatively small part of our entire genome.  Since I'm not aware that any of my close relatives have been tested (yet) and I know most of my close relations, I really didn't expect to find any "cousins" that would fall within the second cousin category or closer -- and I didn't.  Here is what I did discover.

Unlike FamilyTreeDNA, 23andme scans all of your genome to look for patterns that may be used to predict your ancestry.  Mine turned out to be 100% European.  No surprise there.  Here are my results.

I really didn't understand this graphic until I compared it to a graphic for someone that had more of a mixed inheritance pattern.  Here is a sample for an African-American man.

I find it interesting that, as is the case with so many African-Americans, a lot of this man's ancestry is European in origin.  You can go to 23andme, create a free account and explore other sample groups under "Ancestry Painting."

When 23andme compared me to others in their database, the closest relationship they could identify for me was a potential 4th cousin. You can see from the table posted above that I would not anticipate sharing much of my DNA with this person.  23andme computed that we shared 0.48% of our DNA -- big whoop!!! (Note:  I've since found out that the 36 cM we share is a big deal.  Who knew).  Here is what we share in common.

You are reading it correctly.  We share one little section on chromosome 20.  I'll bet I share that much with my husband.  I guess I'm going to have to have him submit a sample.  So come on, cousins, submit a sample!  I want to have some fun.

In my next post, I'll discuss what I found out from a medical point of view.


  1. That's a pretty good chunk of DNA, actually. If you do share that much with your husband you'd best check those family trees a little more carefully! Hope you and 4th cousin to be make contact!

  2. Hi,
    Thanks for the explanation. I was sort-of in the middle of talking about citations and used my impression as a lead in. I fully understand why you might not want all that out there on the Web. That is a valid reason for keeping information private. You can e-mail me anytime,
    Thanks for explaining, it is always good to know the rest of the story
    James Tanner

  3. Susan is right. I'm surprised that they only predicted 4th cousins with that nice stretch. I love the graphic. Good find!
    Above you said, "Unlike Family Tree DNA, 23andme scans all your genome to look for patterns that may be used to predict your ancestry." I'm not sure if you are aware that Family TreeDNA does have an "biogeographical analysis" product in Population Finder, which is a part of their autosomal DNA matching test Family Finder.

  4. The graphic is a great find! And any match over 10 cM long is worth exploring. How long is that one on chromosome 20?

  5. Joan,
    Thanks for stopping by my blog. The segment on the 20th Chromosome is 36cM. I've only recently found out that it is a bigger deal than I thought it was. I'd love to have something to read on that specific topic. I've corresponded with the cousin in question. We've exchanged our extensive family history knowledge and cannot come up with a match. We both have ancestors from Ireland, England, Germany and the Alsace-Lorraine region.

  6. Hi Kathy,
    Check the FTDNA FAQ about centiMorgans:

    I tried to find a similar FAQ for 23andme but didn't specifically find one on centiMorgans. Here is a general overview.



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