Posted by Anna Swayne on August 20, 2014 in AncestryDNA

Last weekend we attended the 2014 International Genetic Genealogy Conference in Washington, DC. Over three days, 500+ people joined together to learn more about DNA testing and how to use it as a tool in your family history research. It was exciting to see so many come out and spend three days focusing entirely on genetic genealogy.

I taught attendees about AncestryDNA and gave tips on how to make the most of AncestryDNA results with the tools we have available online. Julie Granka, PhD, one of our full-time scientists, taught us about matching and the science behind it.

Julie Granka, PhD, Population Geneticist at AncestryDNA

Involvement of the Science Team

Reaching a half-million people in the AncestryDNA database has given our science team a lot of exciting data to look at and carefully analyze. I think it is impressive that we have so many full time PhDs working behind the scenes to improve and make enhancements to AncestryDNA results. This is good for us — we have brilliant minds working hard to make things better for our results.

Let’s quickly review genetic inheritance and how we determine a DNA match, and then we can share Julie’s update. (Jump to Julie’s report now).

Genetic Inheritance

We inherit DNA from our parents (50% from each), and they each inherited DNA from their two parents – and so forth, generation after generation. Looking at the diagram below, you can see that the child inherited random DNA segments from his two parents, 4 grandparents, and 8 great-grandparents. This example demonstrates how one pair of chromosomes can represent the DNA of one’s ancestors.

This inheritance pattern is random and what you get depends on what the previous generation contributed. This is why you and your siblings won’t inherit all the same DNA. But, you’ll inherit some of the same DNA – and that shared DNA is what enables us to find out whether you’re related to someone with DNA matching.

inheritance 50_50

Determining a DNA Match

You share DNA with another individual if the two of you both inherited the same DNA from your common ancestor. Your relationship determines how much DNA you share with another individual. (See the diagram below for an example.) The closer the relationship and the more recent your common ancestor, the more DNA you share. The more distant the relationship is, the less DNA you will share.



We test 700,000 markers across your genome and compare you to every single person who has taken a test in the database and see how much DNA you seem to share with each of them.  Based on how much you share with another individual, we can then estimate if you are 4th or 5th cousins, or maybe you share more DNA and you are possible 2nd cousins.  Maybe you don’t share any DNA and you might not be related at all.

That is the power of DNA — it can confirm relationships you already know about, put you in touch with relatives you never knew you had, or give you new unexpected results! DNA matching really is a great tool in helping us make meaningful connections to discover more about our personal stories. AncestryDNA can help. There is a story inside each of us, waiting to be unlocked.

But the matching process doesn’t end here. Read Julie’s blog post for more insight into how the science team determines whether you and someone else share DNA, and what the science team has discovered by studying the large database of AncestryDNA matches.

We look forward to sharing more of our findings in the future and hope to see you at another event soon. Don’t be shy, come say hello!

Anna Swayne

Anna Swayne has 9 years of experience in the DNA genealogy world. At Ancestry, she leads efforts in developing education to help our community maximize their experience with AncestryDNA. She believes there is real power behind DNA and the story it can unlock for each of us. When she is not talking DNA you can find her hiking or cycling in the mountains or cooking at home.


  1. Ceci

    I’m wondering if this DNA test can distinguish between 1st cousins where mothers are sisters, and half siblings where two persons have the same father AND mothers who are sisters. Thanks.

  2. Adriana

    Danette, a great-grandparent usually shares about 12.5% of their DNA with a great-grandchild. First cousins also share around 12.5%. (These are statistical approximations; the actual amounts could be more or less.) So AncestryDNA is saying that your daughter’s great-grandmother is in the first cousin range in terms of DNA, but can’t predict the actual relationship.

  3. Constance Grubbs

    Being female I know my DNA is lacking. But I have no brothers. I was always told we had Native American ancestry but none showed in my DNA report. Could it be hidden or were my parents wrong? Thanks.

  4. Pamela M Tamez

    I know I am Native American Lakota Sioux and Kiowa on my paternal side.. My DNA results showed that I am Native American. When will Ancestry be able to tell what tribes. Are u in the process of testing people from different tribes? Thank you Pamela Buffalo Woman

  5. Tina Harter-Cruz

    How can a DNA match someone that you know isn’t a blood relation, are you connecting our trees just due to common surnames, supposedly my first cousin is a 99% match, yet we share no blood, his father married into the family and adopted the children, and the son is from another relationship. Yet Ancestry says that we are at 99% match, explain. please

  6. Adele

    Is certain or different segments of your DNA likely to be present at any given time or simply not be visible . I guess I want to know if the composition of your DNA is always constant?

  7. Joan

    We recently had my husbands DNA done through I know he has ancestors from Spain and from Canada, neither of which showed up in the results. Does that just mean that none of his Canadian or Spanish ancestors are in the DNA date base? Thank you so very much!

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