The Concepts Series


Sometimes we get caught up in the details of how DNA testing for genetic genealogy works and what it means. Then someone asks a simple conceptual question, and I have to step back and figure out how to not tell them how to build a clock, but simply answer the question of what time it is.


Someone sent me this query about autosomal DNA matching.

“I do not quite understand how the profiles can be identified specially to an ancestor since that person is not among us to provide DNA material for “testing” and comparison.”

That used to be a common question, but less so now, or so I thought. But maybe it’s just because people aren’t asking anymore, or I’m talking to a different audience.

So, I’m introducing a “Concepts” series of articles. These articles won’t explain the specifics of “how to,” but will explain the concepts of genetic genealogy – just the concepts.  For details, how to and exceptions – and you know there are always exceptions, you can dig deeper.

If you have a basic concept question about genetic genealogy or know of one you’d like to see addressed, drop me a note or attach it as a comment to this article. I’ve discovered that many times concepts questions begin with a phrase like, “Maybe I’ve missed something, but…..”

I’ll be adding the Concepts articles here as I publish them.  And yes, the first article will be “How Your Autosomal DNA Identifies Your Ancestors.”

Concepts Articles



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42 thoughts on “The Concepts Series

  1. “What does matching mean?” I find this to be very confusing for newcomers, especially since there are different interpretations betwen Y, Mt and Au.

    Thank you for tackling this topic (concepts). I find myself reinventing a reply everytime I run into the need for it.


      • Roberta, thanks so much for sharing your knowledge of how DNA works. Here is my question: I have some matches who do not seem to link up to either my maternal or paternal side. I think I know the answer, which has to do with recombination of the genes, but want to make sure of that. My mom tested only with FTDNA (before she passed away in 2012). I have several first cousins (from both sides) who have also tested, and the matches I’m referring to don’t match either of them. Also, my two first cousins from my paternal side share enough DNA with me for us to be considered half-siblings rather than first cousins. I’m assuming this is because our fathers were identical twins and consequently we share more DNA in common than would be likely for first cousins. They don’t seem to matching with the “mystery matches” either. I have compared (via GEDmatch) all my family with these matches as well and none are matching there.

        Thanks for your help.


        • Part of this answer depends on how large those matches are. If they are smaller, they may be identical by chance. If they are larger and don’t match that side, then it could be recombination, or it could be that there is a misattributed paternity someplace that is interfering.

  2. Thank you for taking our questions. Does the number of centimorgans (cM) shared between two individuals accurately determine how closely they are related?

    • Good question. Let me just answer this one for you without making you wait for an article. No, they don’t. They give you a range of possibilities and the further back in time, the wider the range. So think of this as a guide.

  3. Awesome. I know I benefit from hearing something explained different ways and from different perspectives. Sometimes what is clear to person A is muddy to person B. I am looking forward to your articles!

  4. Hmmm, I’m thinking that the general concept of Haplogroups and SNP testing would be nice (for both Y and mtDNA).

    As a separate topic, perhaps a general discussion about the difference between matching some one based on both testers sharing common Y-12 STR markers with estimated Haplogroups, versus matching someone based on both testers sharing common Y-111 STR markers with terminal SNP results. (think of it as the difference between two people living in the same state, versus two people living on the same street, on the same block, in the same City, in the same state.) But maybe that would be a bit more than a “concept”, eh? Thanks again for all you do to educate us.

  5. Thank you for today’s post on Concepts and yesterday’s post on the DNA slide show through the University of Utah. . Although I am relatively new to DNA I find the more you read and reread information the more you understand. Have you written about using the Gedcoms? More specifically using the DNAGEDcom site. I have been able to navigate the GEDMatch site well but am completely stymied by DNAGEDcom. I look forward to your upcoming posts, Wendy Purslow, Oregon

  6. Roberta, Since I match you on FTDNA, if I find the ancestor we connect with can I be confident that where we match by chromosome I can then consider the one for that family when matching others?


    Wilma Smith

  7. I recently had someone ask me questions about Ydna testing. I told them what little I do know which is not much and I am waiting for my brothers Ydna 67 results. Do you have a post about how to read Ydna?

  8. Hi
    Looking forward to your articles and thank you for understanding that this is confusing even for us who try to study it.
    I am interested in how many segment matches make a valid match and how you can figure out which side of a chromosome matches for maternal or paternal ancestry.
    Nancy Thomas

  9. Hi Roberta, This doesn’t fit under Concepts but it might lend itself to another form of administrative How-to article . I am ‘the family genealogist’ and will shortly have DNA from three individuals and within a few months may have 6. Do you have a strategy for dealing multiple individuals? I am testing through FamilyTreeDNA. – Laura

      • Yes multiple kits. There will be 6 kits and ftDNA seems to treat each one as a separate account, so I was looking for a way other than just a spreadsheet to track which kit was in which project and what test per kit has been done. That sort of thing. Administration other than actual genealogy.

        I was originally thinking I’d make a project and have all the kits join it. But I think projects need approval.

        These are newbie questions but a topic that might help people plan or I may have just missed some option when I ordered my kits to place them all under one account. -Laura

        • No, they are all separate accounts at Family Tree DNA. Truthfully, I’ve never “managed” mine in that sense. I remember for the most part and look when I need to. One thing I do have a spreadsheet for is kit numbers and passwords, otherwise I have to look one up every time. You could create a private family project. They do need approval, but I can’t imagine it wouldn’t be.

  10. I thought I was beginning to understand triangulation until I was thrown a curve ball. I had two cousins, from opposite sides of my family, sharing segments of DNA with me at four locations on four different chromosomes. I found that unusual as I’m pretty sure there was no intermingling between the two families, I ran comparisons on GedMatch between the two and they didn’t match up, at all, to each other. How can that be? This throws everything I’m doing into question as far as identifying folks who share common areas of DNA with me – am I missing something at a basic “concept” level?
    Peoria Mike

    • No, you’ve got it. They don’t match each other because they are matching you on those segments from different sides of the family. Makes perfect sense, even though it is a bit unusual that they would match you on the same locations as each other multiple times.

  11. Hopefully, your audience for your subsequent posts on this subject will extend to those who have tested, and also have trees at AncestryDNA. It is shocking that some of these people plaster DNA Icons all over their trees when they have just a tree match, without doing dna segment matching. Some of these are educated people with graduate degrees, who have NOT been educated about DNA; and because AncestryDNA leads them to believe that a tree match is a DNA match. When, if one actually thinks about it, how could that even make any logical sense.

    And, since in the beginning, I actually thought a tree match was a dna match without segment matching, I cannot cast stones. I was one of them!

    How do I know this? I have actually polled some of the people……..and very tactfully.

    • It doesn’t help that you’re lead down that path. Or at least encouraged to go there. Or not encouraged not to:) By Ancestry I mean. Their goal is happy customers and profit for them, not accuracy.

  12. Thank you for the opportunity to ask a question! I realize that to confirm a common ancestor, there must be three people who match each other on the same segment of the same chromosome. My question is: Can a person inherit segments from the same distant ancestor on different chromosomes? For instance, you match two people, each on a different chromosome. Their trees and yours show only one common ancestor couple back to your 4th great-grandparents. Can you still be fairly confident that that is your common ancestor couple even without a true triangulation?

  13. So happy about the new series to come. A recently discovered 3rd cousin had her 95-year-old grandmother take the Family Finder test and is excited to make the most of her results. I tend to jump straight to the “let’s use the tools” part of the learning process, and I need to constantly remind myself to explain the underlying ideas–the ‘why’ . . .

    Interestingly enough, she counts among her matches none other than Roberta Estes! I wonder if this “Roberta” person knows anything about genetic genealogy? 🙂

    • That’s fun. What I do with kits I manage is that if the kit has a middle name in parenthesis, it’s not mine, but someone else’s. However, if it’s just my name and no middle name with parenthesis, then it’s really me!!

  14. Shared, tweeted, followed and bookmarked! In 2016, ALL shall learn how to apply Y chromosome, mitochondrial and Autosomal DNA results to genealogy projects. “Matching,” “haplogroups,” “snps,” ” markers,” “mutations,” and “genetic distance” will be demystified. Yes!

  15. Thank you for always giving us such good information. That and its DNA matching algorithm will drive me crazy. lol I have received a second email today for a DNA match that I no longer have thanks to their revamping of our DNA matches. I actually matched three members of that family before, but now none of them. I do have one match now with that surname but he is not of the previous matches. I do understand the concept of DNA circles and triangulation, but showing me a family tree circle for someone not among my matches is strange. Looking at the new alleged matches, I can see what could possibly be a misspelling of my paternal family name, but the surname that Ancestry is suggesting we match on is on another side of that persons tree. I understand as well that trees have mistakes, but trying to untangle this web makes it even more confusing. The basic question is am I related or not to the current living family who has tested? If we actually are, then we might be able to figure out about the ancestors. For the record, my sister had a similar situation, but the person she was alleged to match to distantly, she actually has some of the DNA matches from that circle and the main person who the email referred to.

  16. I have expanded my Y-DNA at Family Tree DNA to 111 and found only one match. It seems not very many people are at the 111 mark.What concept of this expanding to 111 marker can I use toward finding or furthering my DNA and family research?Thanks.

  17. My question has to do with endogamy. I know several of my ancestral lines are affected by this this concept such as my Acadians, Scot Irish, and just a group of folks that lives in Old Dobbs, NC–now the counties of Lenoir, Wayne, etc. I encounter blocks of matches that all triangulate and I think that’s what I’m seeing. It’s easy to know when I find that most of the people in the block have obviously Acadian names in their lines, but the ScotIrish and others can be more difficult to pick out. Can you give some general DNA characteristics that help identify these groups, what patterns of them might look like on dnagedcom’s ADSA, and any other tricks you’ve picked up along the way? Thanks!

  18. I have a match at FTDNA which is also on GEDmatch. She tested at Ancestry, I tested at FTDNA. We match at both place, and although our main 35cM segment is the same, the around 1 cM ones are different. What should I understand from these mismatches 1 cM segments?

  19. Pingback: 2016 Genetic Genealogy Retrospective | DNAeXplained – Genetic Genealogy

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