DNA Testing for Genealogy – Getting Started, Part Three

Posted August 1, 2012 by Geni | 26 Comments

We’re excited to bring to you a special guest series by genetic genealogist CeCe Moore. Some of you may recognize her from her blog YourGeneticGenealogist.com. For the next few weeks, she’ll be providing a great overview about DNA testing for genealogy. Enjoy!

This week we are finally going to discuss my favorite type of genetic testing for genealogy – autosomal DNA. For the past two weeks we have covered DNA tests that are solely informative of one ancestral line – direct paternal (Y-DNA) and direct maternal (mtDNA). The great news about autosomal DNA (atDNA) testing is that there is potential to find valuable and meaningful information about any of your ancestral lines.

This is because all of us, male and female, inherit our autosomal DNA from our parents. Fifty percent of our atDNA comes from our mother and 50% comes from our father. Since our parents each received 50% of their atDNA from each of their parents, it follows that we inherited about 25% of our atDNA from each of our grandparents. This percentage, which is somewhat variable, is cut in half with each generation as we go further up our family tree. As you can see on the chart below, we inherit about 12.5% of our atDNA from each great grandparent and about 6.25% from each of our 2nd great grandparents.

The amount of autosomal DNA inherited from our ancestors on average (Credit: Angela Cone)

The Basics

Without getting too technical, all healthy human cells possess 23 pairs of chromosomes. We receive one set of these 23 chromosomes from each of our parents. Chromosomes 1-22 are called the autosomes. The 23rd pair is what determines gender. One X chromosome from mom and one Y chromosome from dad, results in a male and one X chromosome from each results in a female. The autosomes are the focus of the type of DNA test we are discussing today.

When you submit a DNA sample for an autosomal DNA test, the testing company will compare your atDNA to that of everyone else in their database, searching for people who have significant stretches or “segments” of atDNA in common with you. If two people share enough atDNA, then it follows that they must have inherited it from a relatively recent common ancestor. Based on this principle, you will receive a list of matches with a prediction of how closely related the testing company estimates you are to each. Generally, the more atDNA two people have in common, the closer they are related and, thus, the more recent their common ancestor(s).

Since autosomal DNA, unlike Y-DNA and mtDNA, undergoes mixing (recombination) every generation, its usefulness quickly dissipates for genealogical research more than five or six generations back. Because of this, it is advisable to test the oldest living generation whenever possible. This isn’t to say that you won’t occasionally find an atDNA match with a cousin more distant than third or fourth, but the odds become increasingly smaller, so it is far from guaranteed.

What can atDNA testing do for me?

In my opinion, there are three important aspects of atDNA testing for a genealogist. The first is finding previously unknown cousins who can either help you get beyond a genealogical brick wall or provide you with other new information about your shared ancestors. The second is testing known relatives to confirm relationships and, in doing so, identifying DNA from specific ancestors. The third is receiving a percentage breakdown of your “ethnicity”.  The first two are within the scope of this post and the third will be discussed next week.

Since we inherit atDNA from all of our relatively recent ancestors, there is potential to discover a match in the database who shares descent from any of our ancestral lines. This includes those that are currently brick walled within the last couple hundred years or so. If, for instance, you have a brick wall at the great-great grandparent level in Sidney, Iowa with the surname Travis and you find a predicted third cousin match with a person who has ancestors with the Travis surname in Sidney, you may be able to gather enough information from your match and/or this nudge in the right direction to demolish that brick wall. This may even hold true for an unknown maiden name of one of your female ancestors if you are lucky enough to find a strong match in the right geographic area.

One of the most meaningful aspects of atDNA testing is confirming genetic descent from our ancestors that, so far, have only existed in our present-day lives on paper. Each time I confirm a common ancestor with one of my matches, I have taken a step toward authenticating that branch of my family tree. Let’s face it, no matter how good the documentation, it is simply impossible to know for sure that our ancestors are always who they are supposed to be on paper. However, with several DNA matches who can document descent from the same common ancestor(s), we can feel quite confident that our research on that part of our tree is correct.

My 22 autosomal chromosome pairs in gray, paternal and maternal genetic contributions top and bottom

I have been testing my known cousins for some time in order to “map” my chromosomes to my great grandparents. For example, if I test my known Proctor second cousin (who shares no other ancestral lines with me), then I know that any shared atDNA that we possess is inherited from our common great grandparents. A genealogist can systematically test known relatives to determine which portions of their chromosomes were inherited from which of their ancestors. This process can also be used to confirm traditional research as described above. So far, I have tested multiple cousins from each of my ancestral lines and confirmed that my great grandparents are indeed who I thought they were. In the image to the right, you can see the beginnings of my “chromosome map,” color-coded to illustrate which portions of my autosomal DNA were inherited from whom. 

New Possibilities

I have been interested in DNA testing for genealogy since 2002, but I didn’t get really excited about it until 2009 when 23andMe introduced Relative Finder, the first version of autosomal DNA matching for genealogy, and Family Tree DNA soon followed with their version, Family Finder. I was immediately hooked. What I really love about atDNA testing is the possibilities, the almost unlimited potential for discovery. For the dedicated genealogist venturing into atDNA testing, with perseverance, there is much to be gained.

A few examples of discoveries made from atDNA testing:

  1. I found that I have distant Jewish ancestry about which I might never have known without atDNA testing. My colleagues and friends Dr. Tim Janzen and Andrea Badger confirmed Jewish descent as well.
  2. Tim also confirmed Native American ancestry in his family.
  3. My brother-in-law learned of African ancestry and, as a result, uncovered a direct descent from Thomas Jefferson.
  4. Adoptees have discovered close family members and reunited with birth parents.

Although atDNA testing is full of promise, it is not recommended for those who desire quick and easy answers. Contrary to some people’s expectations, the testing company will not populate your family tree with your missing ancestors (maybe someday). However, I believe that atDNA research is a perfect fit for the devoted genealogist with an already well-researched family tree. Many of us jump for joy when we discover a new tidbit about an ancestor after years of searching.  Just imagine how meaningful it is when presented with living evidence of your ancestors’ existence that is inside of you? If you give it a chance and are willing to work hard at it, autosomal DNA testing can be an incredibly rewarding experience.

Next week, this series will conclude with a discussion of tests that provide percentages of “ethnicity” and a summary of what I hope you have learned from this series.

(Update: Read part 4 here)

CeCe Moore is a professional genetic genealogist and writes the popular blog Your Genetic Genealogist. She is the Southern California Regional Coordinator for theInternational Society of Genetic Genealogy and the administrator of the organization’sDNA Newbie Yahoo Group. CeCe serves as an “Ancestry Ambassador” to 23andMeand on the advisory board of the Mixed Roots Foundation and is a member of Mensa. Her favorite genetic experiment is her seven-year old son, Nicolas.


  • Andrew Colman

    Another excellent article!

    • CeCe Moore

       Thank you Andrew!

  • israelp

    You obviously know what you are doing and you make it sound easy. Then you start talking about what exactly is on which chromosome and my eyes blur. There doesn’t seem to be much explanation of that for the layman.
    I’d like to hear more about your Jewish ancestry. “Ashkenazic” covers a huge amount of territory. Maybe you can be more specific.

  • Carl H Bloss

    Is there a way to know by the questions you need answered to choose the best testing form – autosomal for relatives, etc. ?

    • CeCe Moore

      Hi Carl,
      In my next post, I review those types of questions. It will be posted by tomorrow afternoon, I believe, so please check back. If it doesn’t answer your question, just post a comment and I will follow up with you.
      Thanks for reading!

      • CeCe Moore


  • Mglamar

    Great article … and thank you for sharing … I have also done 23 & Me.  You made the following statement  “A genealogist can systematically test known relatives to determine which
    portions of their chromosomes were inherited from which of their
    ancestors”. I am trying to figure this out.  I have over 500 new relatives and I would like to know if they are Maternal or Paternal. 

    • CeCe Moore

       @f9fe6bd456acae3e4f30c46150606b7b:disqus  – What I meant was that a person can test KNOWN relatives like parents, grandparents, half-siblings, aunts, uncles and cousins in order to determine which portions of their DNA came from which ancestral lines. This is useful because it can then help pinpoint the ancestral lines that you should look at for common ancestors with your matches based on where your predicted cousins (unknown relatives) matching segments are i.e.-which chromosome and the start and stop points of the segments. Read the blog post I linked to above by clicking on “testing my known cousins” for more details.
      If you just want to know which are maternal and which are paternal, you should test your parents, if available. Anyone who matches you should also match one of them. If they aren’t available for testing, then try testing aunts or uncles from each side, if possible. (Half-siblings work well too.) If that isn’t possible either, then test first cousins from each side of your family. You won’t be able to separate out ALL of your matches by testing any of these relatives other than your parents, but it will help. I use these techniques in my own research, so follow along on my blog if you want to learn how to do it.
      I hope that helps. Thanks for reading!

  • CeCe Moore

    For anyone thinking of ordering an autosomal DNA test, there is a sale at 23andMe today through Sunday. Details are on my blog: http://www.yourgeneticgenealogist.com/2012/08/23andme-offering-50-off-their-personal.html

    • Lavinia Lee McKinney

      I did the autosomal test at 23andme and should have my results in a few weeks.Will this help me with a few brickwalls on both sides of the family going back 3-4 generations?

      • CeCe Moore

        Hi Lavinia,
        It depends who else is already in the database and the nature of your family mysteries, but there is a good chance that this test will help you with your research, especially since your brickwalls are relatively close.
        Good luck!

  • http://www.facebook.com/chuck.sumner.54 Chuck Sumner

    Absolutely awesome description. I have about 6 weeks total experience with anything DNA, but 23 years of experience in Genealogy. I’ve bookmarked your main Genetic blog as well. Can’t believe how interested I got in this, but might be due to my son’s interest in Biology now. Great work!

  • Janice Cronan

    CeCe I am a member of APG and thought they would archive your webinar from September, but evidently they did not. I missed it because it was on our Bay Co. Gen. Soc. meeting day and time. Do you sell any of your recorded presentations? I heard you earlier this year speaking with a genetic genealogist by the name of English? at a Southern California Radio presentation? My maiden name is Moore and we have communicated before because we belong to Moore Worldwide DNA. My brother’s sample placed us in group 2. I also have done the Ancestry.com and 23andMe, and continue to try to learn all I can about genetic genealogy. I really would like to get a copy of the presentation you did in Sept. for APG. Thanks.

  • soconfused

    I’m confused about who a female can trace and who a male can. I matched up with a male but not with his mother (from which I understand, that’s the only way I can trace since I’m a female). So that means, I must match through his fathers side. Right?

    • Elizabeth

      soconfused, Yes, if you match him and his father, then you are related to him via his father’s side. You can match males and females with autosomal DNA.

  • EDRW123

    My Dad and I have both done autosomal testing. He has done testing through both ancestry.com and familytreedna, and I have only tested through ancestry.com. We both match a gentleman on ancestry, estimated 4th-6th cousin with 96% likelihood. My Dad matches a lady on familytreedna, estimated 2nd-4th cousin with 74.88 Shared CM. Each of us also has our raw autosomal data uploaded to gedmatch, and we both match both of these people there as well, at a range of roughly 3.9 – 4.0 generations. We noticed there is a common ancestor shared by the two matches we both have, and through contact with this family, we’ve learned more about their origins and ancestors. The common ancestors shared by these two people (who also match my Dad and I) are a couple who born about 1865. I also have to add in the fact that my Dad’s paternal Grandfather was adopted, so we don’t know anything about his adopted Grandfather’s paternal or maternal line.
    Now, the wife of the couple who are the common ancestors of my Dad and I’s matches died, and then the husband married again and had more children. My Dad and I do not match the descendants of those children. Would I be correct in assuming then, that our relationship to our matches must be through the first wife’s family? We only match the descendants of her children, not the descendants of the second wife. Could we be matching through a sister of hers, or an illegitimate child of hers, or through her mother? The only thing we know is that somehow we fit into their family tree. As a non-expert, it’s a bit confusing! Thanks for any help you or anyone else might provide.

  • scyounts

    Thanks for the very helpful article. I can now plan my testing with more confidence, and begin to understand the resulting data.

    I wish I could find recommendations that are that specific and clear on the best way to organize the paper and digital data I have already collected. There are so many possibilities. I guess multiple choices are essentially a good thing.

    By the way, it is interesting that you coincidentally picked a great great grandfather from Sidney, Iowa as an example. Perhaps that reference was not personal to you but most of my relatives on both sides, including some Proctors, come from that locale. Additionally, one of my genealogical quests concerns a great great grandfather from Sydney (surname Hinkle).
    Thanks again for sharing your expertise.

    Steve Younts

  • scyounts

    I just attempted to purchase a testing kit and a message popped up that 23andMe is not currently able to offer this service in Maryland. Something to do with state regulations on clinical testing. They also recommend NOT circumventing the ban. Any thoughts, anyone?

    • JGK

      I had the same problem with New York. I just purchased the kit and drove to Pennsylvania to ‘spit’ and mail the kit.

  • RoH

    Hey CeCe! I just ordered the 23andme kit because I wanted to find out my family roots on my dad’s who is deceased. I am a female. Is this the autosomal test where I can receive info about my father’s mother’s roots? Do I need a male family member to test for me?

  • Wisrthu

    Hello CeCe
    I tested with ancestry then uploaded to 23 and me, gedmatch, and I tested with genebase. I know my maternal side and have it uploaded, but I do not know my fathers name, I only know where they met. My mother has died, and she was an only child. How can I find my father through atDNA? Is there someone I can hire to decipher it all?

  • Lady R

    How do I find out what my mtdna is?

  • Guest

    notice on the first 10 kit numbers on my one to many match list, most are under 20 cms on various chromosome’s. Is it worth it to investigate those low numbers? As viable matches for comparison of our family trees? Thank you.

  • chekwriter

    just noticed on the first 11 kits chosen for comparison, most are under 20 cms on the various chromosomes. Is it worth it to take the time to investigate those matches. Is there a chart that equates the value of cm’s to actual nearest related present day cousins? Thank you.

  • Pamela Bangs

    Why does CeCe Moore only answer certain questions? Are the other questions not as important?