Limits of DNA Testing for Family History

Diahan Southard

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When it comes to setting DNA testing goals for family history, you have to know your limitations. You want realistic expectations! Increasingly, the list of what DNA testing CAN’T do is getting shorter. But there is still a list. Here it is.

DNA testing limitations What DNA Cant Do Limits of DNA Testing for Family History DNA Testing Goals IO (1).png

What DNA Alone Can’t Do

Can-do people rarely like to talk about what just. isn’t. possible. But the truth is, if you don’t know your limitations, you might set unattainable goals which lead to disillusionment and frustration down the road.

Good news: the list of what DNA can’t do for your family history is getting shorter. More people around the world are testing. DNA tools and analysis are improving. But there are still limits. Here are four things that DNA all by itself simply cannot do for you.

1. DNA can never provide the name of an ancestor.

DNA alone is not going to deliver your ancestors’ names to you on a genetic silver platter. (Tree reconstruction tools such as 23andMe’s Family Tree, MyHeritage’s Theory of Family Relativity and AncestryDNA’s ThruLines are pushing this direction, but none are foolproof and the latter two require family tree data—and of course you have to have DNA matches who point you in the right direction.)

Now, if your close relative tests at the same company—and the screen name they use is their real name—then yes, you’ll get their real name delivered on a silver platter right to your match list. But what I’m talking about is the identity of your ancestors: grandparents, great-grandparents, etc.

Your DNA Guide the Book and Finding an Ancestor Quick Reference Guide.pngWhat DNA CAN do: your DNA test results can eventually lead you to the identify of unknown ancestors, but you also need a healthy stack of real genealogy records, family tree data, fruitful DNA matches and good analysis. My quick reference guide, Finding an Ancestor Using Your DNA, introduces this methodology, which I cover even more extensively in Your DNA Guide—the Book.

2. DNA can never provide a definitive relationship.

Even with the amount of DNA shared by biological parents and full siblings, there is always more than one possibility as to how you’re related to someone. The more distantly you’re related, the more possibilities for how you’re related. The genetic distance between even these half-sisters, below, allows for several possibilities for how they might be related:

DNA testing limitations half siblings relationship possibilities.jpg

What DNA CAN do: As shown above, DNA gives us a genetic relationship range, or list of possible relationships. We have to use other resources—historical records, trees, DNA analysis—to help us figure out which of the possible relationships is accurate (or at least most likely). I walk you through this process in Your DNA Guide—the Book.

3. Autosomal DNA cannot currently reach back farther than five or six generations.

Autosomal DNA testing is most common kind of DNA testing. That’s what is sold by AncestryDNA*, 23andMe, MyHeritage, Living DNA and Family Tree DNA (the Family Finder test). It’s great because it reveals your heritage on both sides of your family tree. Five or six generations sounds like a lot, but many people want to go deeper than their 3x or 4x great-grandparents.

What DNA CAN do: Those five or six generations have potentially produced hundreds or even thousands of living relatives. DNA can help connect you to them and can reveal clues about how you’re related to them. (In the process, you may come across a lot of removed cousins.)

Connecting with your DNA matches can help you rebuild your family tree—along with your sense of family identity and connection.

4. Y DNA and mtDNA have strict inheritance patterns that limits their use.

Y DNA testing is only available for genetic males, and looks only at paternal lineage: a man’s father and his father and his father, etc. mtDNA testing (which everyone can do) looks exclusively at the lineage of your mother, her mother, and her mother, etc. A lot of relatives who don’t fall on those lineages—such as your mother’s father’s mother’s people—are untouched by your YDNA and mtDNA tests.

What DNA CAN do: DNA does reveal unique clues about your maternal and paternal lines, and can connect you with relatives on these lines (though often, much more distant relatives). You can learn about deeper ancestry and migration patterns through their haplogroup assignments. You can also use Y DNA and mtDNA in targeted ways to ask specific questions about these branches of your family tree.

DNA testing limitations: Not so limiting, after all

In setting out to clarify what DNA cannot do alone, it looks like I couldn’t help but reveal what it CAN do when you bring your best game to it. Now it’s your turn to see what DNA can do in your family tree. Our inexpensive “Finding an Ancestor Using Your DNA” Quick Guide will show you the way, and open up doors to all the ways DNA help answer your family tree questions.

Take me to that Quick Guide!

Which DNA test should I take?

As with most things, it depends on your situation and goals. But we’ve got you covered with expert comparisons of the DNA testing companies!

Read our DNA Test Reviews

<a href="" target="_self">Diahan Southard</a>

Diahan Southard

As founder and CEO of Your DNA Guide, Diahan Southard has been teaching people how to find family history answers in their DNA for several years, and she's been in the genetic genealogy field since its infancy. Diahan teaches internationally, writes for popular magazines, consults with leading testing companies, is author of Your DNA Guide–The Book, and producer of Your DNA Guide–the Academy, an online learning experience.

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  1. Chris Schuetz

    I totally agree that for most people, 5 and 6 generations are a practical barrier. A small proportion of genealogical cousins are beginning to share no DNA with us, and the proportion gets bigger quite quickly after that.
    And you need to build your tree out that far at least to make sense of matches.
    So, do you just have to wait for more matches to come in at this level, or can you do more with what you already have? If you have a tree out that far, confirmed by DNA, then it is possible to stretch a little further here and there. The number of genetic matches actually increases in the next generation (5C)*, but the average match is only 25cM, so many of these are not useful due to Ancestry’s 20cM cap on Shared Matches. At MyHeritage the restrictions are less, and I have found some good connections from there.
    Tree accuracy on both sides of the match becomes a more limiting force.
    As matches become smaller, they become more uncertain, so I like to find more evidence to support things – maybe a will or land transaction. Especially one more generation further back.

    • Diahan

      Thanks for sharing these thoughts, Chris. It sounds like you have a good perspective on things. So yes, I think you can move cautiously forward with the smaller matches, just keep your limitations in mind.

    • Deb

      I have found that my best use of DNA results to-date is to verify my paper-trail. I have found potential ancestors also in Thru Lines and was able to use this information successfully as hints.

      • Danielle Francis

        That’s a great strategy Deb!

  2. Mary Ellen

    I think more people should include siblings for all direct ancestors in the family tree. Many times I review a tree and think if only siblings were included I might be able to figure out relationships for the past generations.

    • Terry (pockets)

      I’m guilty of this! But now I realize that I have a lot of additional family relatives that I should be adding to my family tree.

    • Kathy M

      I wasn’t doing that but started too. I do think I makes a better picture. I am doing a tree for a 1st cousin as well and make sure to do it complete as well. I am going back and fixing where I missed. I was a bit hesitant at first because my parents each had 14 & 12 siblings in the families and I was exhausted after the 1st generation LOL!!!

    • Marie Kathy Morrissey

      To Clarify: is it important to put in the decendents of all your aunts and uncles? Or is this most important for higher level in the ancestry?

      • Diahan Southard

        It depends on your research goal. If you are looking for someone more distant, then focus on the descendants of those ancestors. I wouldn’t worry too much about your aunts and uncles children.

  3. Drew Downs

    My 3 ggf John Morris (1816-1887) KNVM-Z1D in FS is a brick wall. I know a lot about his family, but not his out his wife’s parentage. Most of my DNA matches are on my father’s side. Is there An easy way to find which DNA matches are close to her and his wife? I am using Ancestry DNA.

    • Diahan Southard

      Hi Drew. Finding a 4X great grandparent (the parents of John and his wife) is just beyond what Autosomal DNA can reliably reach. The amount of DNA that you share with those 5th cousins who are his descendants is just so small, it is difficult to know if it is because of your connection to this 4X great couple, a different 4X great couple, or just because that piece of DNA is common. Plus, the way we gather matches into groups is by using the shared matches tool, and at Ancestry, that tool will only gather people sharing at least 20 cMs, which 5th cousins often aren’t. So, I have painted a pretty dismal picture, haven’t I? You could turn to YDNA to help with John’s family, and mtDNA to help with his wife. But I think until we have better Autosomal DNA technology, I am just not sure how successful you will be.

  4. Carolyn Lea (SCHWARZBAUM) PhD

    My father was Ashkenazi so I am dealing with endogamy that makes matches appear more closely related than they actually are. I know you spoke a little bit about this at ROOTSTECH and so did Kitty Cooper as well as one are two others. How do we decide which matches to follow up on? What should the longest segment strand be or do you look at other things as well?

    And FTDNA has cut my brother’s % and mine of Jewish DNA – my brother to only 44% when we were at 50 to 51% for the three of us – my sister as well. Guess they updated their algorithm. They increased our Scandinavian percentage when I only have one family from that area. Migration patterns seem to become very important when doing research.

    • Diahan Southard

      Endogamy is tricky. In fact, I created an entire course just to answer your question about which matches to focus on: But the short of it is, you don’t want to look at anyone who has a longest block under 15 cM, 20 cM if you want to be extra sure.

  5. David speth

    I don’t know who my father is and my mother didn’t know is what she said and I did ansestrey and got a close match but the tree manager had no interest in hereing about me so I stalled out

    • Diahan Southard

      Hi David. I am sorry to hear that one of your DNA Matches hasn’t shown as much interest as you would hope. If you do have a close match, and you haven’t yet identified your father, you may be able do do without the help of you matches. You might try this free download to help you learn a little more:

  6. Jane

    Hi Dianne – which of your courses do you suggest for following scenario. My friend is African American/decendent from slaves. His father and paternal grandmother are unknowns. The state records are closed. I’ve built 75+ trees for his close DNA matches and for some, ID’d common ancestors (but those associated to unknown ancestors are limited which is what i need); I’ve done LEEDS method (some overlap) and some relationship assessment. I do have a confirmed white ggf/gggf and have narrowed my pool. I feel like I have data but not seeing / using it effectively. Currently reading your “DNA Guide book”. I have Ancestry DNA on several other sites.

    • Diahan Southard

      Jane, the ideal next step would be the DNA Skills workshop. That way we can start at the beginning and work through much of the work you have already done to make sure you did it systematically, and then continue your progress through the full process. Our next class starts Tuesday, March 22.

  7. Tamsen Munger

    I am looking for my 3rd Great grandfather on my mother’s side. Unfortunately I have very little DNA to go on. I have the Y111 DNA from my mother’s first cousin (Jim McCrory) and my own brother’s Y111 DNA.
    There is a lack of family to get DNA from. My mother had one first cousin, Jim, I do not have any first, second or even removed cousins from my grandfather’s side. The family going back 4 generations died young or didn’t have offspring. (on my grandfather’s line – out of 6 siblings there was one male child, Jim, one female child, my mother) So far the closest DNA matches my cousin Jim has are 53 cM. (I am the administrator of his DNA on Family Tree). He does not have living children.
    Do you have any suggestions?

    • Diahan Southard

      It is really tricky to use DNA when there just isn’t that much of it around. I would have Jim and your mom tested at all companies. I would also have any cousins you can find on your mom’s other lines tested. That would help you eliminate matches from other lines. Then it is really about working with those few matches you will find who you can be confident connect to the line you are researching. Do you have my book? It would help you do all the elimination of matches you need to do to make sure you are looking at the lines that connect to this branch.

  8. Marie Kathy Morrissey

    Not sure what category this question should be in but, I have people showing a DNA relationship that are more distant cousins, some are in the country where my grand parents parents lived I am trying to find. I think by looking at a number of these and seeing if they are related to each other (triangulation in my heritage), I think I may be closing in on surnames that may be common in our ancestry that were prior to DNA testing unknown to me. There appears to be a couple surnames that come up with different people that show up related to me. They do not have very good trees, so it’s hard. Since my tree basically ends with my maternal grandparents on the side I want to find ancestors, my tree is really not very helpful. My limited info has been no help to anyone. (It is different on my father’s side but I am concentrating now on my mother’s side. I have extensive information on my father’s side.) Maybe someone could talk to me about this as this is all becoming a bit overwhelming and I am having trouble determining where I should focus.

    • Diahan Southard

      Focus is so difficult, isn’t it?
      I have found that using the match labeling system ( keeps my matches organized and helps me know a little bit about how they are related so I can focus on the right lines. Then yes, it is about building out other people’s trees.

  9. Jim Bruce

    My FTDNA autosomal admixture test results for Scandinavia is 30%. However, my “recent analysis” test results for CRIgenetics is only 2.5% Scandinavia! To further confuse me, according to CRI’s “Advanced Analysis,” 29.5% of the “oldest” ancestries in my genetic makeup arose somewhere within the geographic locations of Finland, Sweden, Norway, Russia, Denmark, Estonia, Lithuania, Latvia, Belarus, Ukraine, Poland, and Kaliningrad.

    U.S. census records indicate that my paternal great grandfather was born in Norrbotten, Sweden. My YDNA test results puts my more distant ancestors in Finland.

    Is there any way to make sense of this?

    • Danielle Francis

      Hi Jim, we see lots of situations similar to what you’re describing, it’s not uncommon to see differences in ethnicity reporting between companies, or even changes within the same company over time. Our free guide explains why this happens, you can download it here:

  10. Paula Johns

    Hi can you give me any advice please where to go next .i have taken dna on ancestry and my heritage as I’m looking for my biological father and grandfather which are both unknown .my mum has passed away so I can’t get any information from her.i have connected with 2nd cousins but it’s so hard as can’t find links. Can u help in anyway to go forward please ?

    • Danielle Francis

      Hi Paula, you’re already on a great track by having your DNA test results! Check out our free guide for tips on what to do next to find your biological father and grandfather:

  11. Wendy Miles

    Hello Diahan,I’ve been doing Family History for a bit over 60 years made easier as Internet came along & various Genealogy clubs etc. I have trees with Ancestry- [where I tested autosomnal DNA ]- & My Heritage. I concentrate mainly on my Legacy software & have just short of 7.400 names there-in.
    Many ‘matches’ are known to me mainly paternal side in Australia, Maternal in UK, often difficult to place.

    My main inerest is finding ‘proven’ 2nd Gt. G’father in UK, found in Liverpool 1822 – 1843. I found his wife’s family & their children, survivng few I found knew nothing of fore fathers- they said, so I filled them in. Their father wasalso a mariner & youngest surviving son.

    A family with people I’ve found who fit nicely as 2nd Gt. G’father’s parents -all mariners – same area, but no proof. Similar naming patterns fit also but I would like to know for sure. One match on M.H. has same name for 2G.GF.’s mother but different for Father, he has this from his father. No-one else has come up with same as mine.
    I have no siblings left, one Gt. Nephew has tested but is in an occupation where this is not advised so I hesitate to ask him about any matching. He has no tree.
    p.s. I am carer for my husband & can’t always find time to keeep adding to both of the online trees, so they are not large.

    I tried to buy your EBook but bank fluffed up my accounts so it didn’t
    happen, fixe now so I can go ahead.

    • Danielle Francis

      Hi Wendy, thanks for your comment. The ebook will be great for helping you figure out what to do next to narrow down and confirm who your 2X great grandfather is. Good luck on your research and let us know if you have any questions along the way!


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