DNA Q&A: Ask Us Anything!

Here at The DNA Geek, we want you to solve your DNA puzzles.  Sometimes, that means research-for-hire, and sometimes it means giving you the information you need to help yourself.

That’s what the DNA Q&A series is all about!  Have a question?  Just ask!  Think of this as a relationship advice column but for genetic genealogy rather than bad lovers.

Let’s get started with a few questions from “P.E.”, who contacted me via social media.  P.E. asks:

I am an only child and my elders have all been long passed. Does DNA have any particular value to me?

Yes, it does!  While it’s better to test your parents than yourself when it comes to autosomal DNA (atDNA), that’s not alway possible.  In fact, it would also be better to test your grandparents than your parents, and your great grandparents than your grandparents.  But few of us can do that, so we test the generations we’re able to.

Image by dandelion–tea/Pixabay

Although you only inherited half of the atDNA of each parent, you still carry plenty of their DNA and will “match” relatives who are related to each of them.  These matches are people who share DNA with you via a common ancestor.

In general, the more atDNA a match shares, the closer the relationship.  Sure, it would be better if you could have tested your parents, because they are one generation closer to those relatives than you are, but you work with what you have.

There are other types of DNA test, as well:  Y-chromosome DNA (Y-DNA) and mitochondrial DNA (mtDNA).  As a chromosomal male, you have both, inherited from your father and mother, respectively.  Y-DNA can only trace relatives on your direct patriline (father’s father’s father’s etc.), and mtDNA can only trace relatives on your direct matriline (mother’s mother’s mother’s etc.)  On the other hand, these types of DNA have the advantage of not being “diluted” the way atDNA is.  In other words, a Y-DNA test on you is almost as good as a Y-DNA test would have been on your father or grandfather.

How do I decide which DNA testing company is best for me?

That’s a good question, but perhaps a better one would be “Which one is best for me first?”  Because the truth is, once you catch the DNA bug, you’ll want to be in more than one database!

The best place to start is with AncestryDNA.  I say this for a few reasons.  First, they have the largest database by far—more than 20 million people.  And the larger the database, the more likely you are to find DNA relatives who can help your genealogy research.

Second, they have some great built-in tools for working with your DNA matches, and enthusiasts have created additional tools that you can install on your internet browser for free.

Finally, the smaller databases, like MyHeritage, will let you upload your AncestryDNA data file rather than having to pay for a whole new test.  These sites may charge a small fee for a full suite of tools, but it’s cheaper than buying a second (or third) test.  AncestryDNA does not accept uploads, though, so if you tested in one of the smaller databases first and then wanted to try AncestryDNA, you’d have to purchase an additional kit.  You might as well just go there first!

How does DNA help me trace individuals related to me?

Your genealogy DNA company will “match” you to other customers who share DNA with you.  With atDNA, the more DNA they share (measured in either percent or a unit called centimorgan), the closer the relationship generally is.  The testing company will give you a rough estimate of the relationship to guide you.

A great, free tool for interpreting your atDNA matches is the Shared cM Tool at DNA Painter.  You can read more about the tool here.

Where can I obtain understandable guidance, once I get my results?

Believe it or not, one of the best places to get help with your DNA results is Facebook!  There are dedicated groups for genetic genealogy in general, for each of the testing companies, for specific geographic regions and populations, for third-party tools … you name it!  For example, I run a general DNA group called The DNA Roundtable, one dedicated to the What Are the Odds? tool at DNA Painter, and one for Louisiana Cajuns and Creoles.  Group members enjoy sharing information and helping one another.

There are also blogs like this one, which are free, as well as practical books like Diahan Southard’s Your DNA Guide: The Book.

If you need one-on-one attention, you can also do a paid consultation with myself or another qualified genetic genealogist.

There are lots of options to choose from!

Have Questions About DNA?

Just ask in the comments!  Your question may show up in a future column.

Disclaimer:  All dating advice will be limited to tMRCA (time to most-recent-common-ancestor).

Many thanks to genealogist and graphics wiz Michelle Custer Bates for the title graphic!

39 thoughts on “DNA Q&A: Ask Us Anything!”

  1. As an adult with a parent that although I have the absent parents name and a little family information I have hit a wall. I have made it my goal to find a picture of him. I have gone every route I know but came to the conclusion that with out 50’s census I have no idea where he went to school. Did he ever marry or have kids? His dad was in the military and his parents married twice. Sadly by the time I even got a name my mother had Alzheimer’s so she was not terribly forth coming with info. His name was not listed on my birth certificate. It was suggested to me that I could probably find school pictures but he was born in 1931 and I truly have no clue where he went to school. I guess what Im saying is at almost 68 years old I would like to see a feakin picture of this man or his parents…..

    1. Fortunately, the 1950 US census will be available soon! In the meantime, have you done a DNA test to confirm that you’re looking at the right family?

    2. I’ve been trying to identify my paternal grandfather for many years.
      My father is deceased but my full brother has done Y37 and autosomal.
      Using many low cm autosomal matches, I have created a WATO tree. There is one Ydna match that fits in this tree. I do not have autosomal results for him.
      Does this mean I am
      (Hopefully) barking up the right tree?

      1. The answer depends on how strongly the Y-DNA results point to a specific surname and how close the atDNA matches are in WATO. Ideally, you will find both strong atDNA matches and documentary evidence that can rule out other potential men until you’re left with just one. Sometimes, that means asking people to test for you. If you need help with WATO, I recommend the dedicated Facebook group: https://www.facebook.com/groups/WhatAretheOdds

        If you’d like one-on-one help, I offer paid consultations. https://thednageek.com/contact/

    1. How far back have you built out your tree on your mother’s side? Do your maternal matches have trees? Were her family recent immigrants?

      1. More info from my maternal side- ancestry trees–but no thrulines. I know much more about my mother’s family. Maybe I don’t get the concept of Thrulines.

        1. ThruLines try to find connections between your tree and those of your matches. It can’t find connections if your tree isn’t deep enough, if your matches’ trees aren’t deep enough, or if your relatives on that branch haven’t tested.

  2. How accurate do you find the thru lines in Ancestry ? I have a low cM count (11) with someone in thru lines however I was able to track the connection back to my 4th GGF/GGM 2 sons.Thanks

    1. ThruLines are only as accurate as the trees in the system, I’m afraid. Just like other members’ trees, they’re great as hints to follow up on.

  3. Can you explain what to do with a Y DNA test please? Hubby has many results, some with his surname, many without. How do I use the results to further my research?

    1. Your best bet would be to join some of the group projects at his testing company. Look for ones for his surname, for the surnames of his matches, and for his haplogroup. The well-run projects have active and knowledgable administrators who can help with your husband’s specific genealogy questions.

  4. I always understood I shared ~50% of my DNA with my siblings, but MyHeritage tells me that the 2643cm match is a 3/8 share (37.3%). Why might that be?

    1. Two reasons. First, while you share exactly 50% of your DNA with each parent (and each of your children), the amount you share with full siblings averages 50%, but can be higher or lower. Secondly, full siblings share some regions of DNA through only one parent and some through both parents. MyHeritage only counts those “fully identical regions” once rather than twice, so the total they report for full siblings never reaches 50%. If they counted the FIRs twice, you’d be much closer to the true average.

  5. This may sound confusing or silly but it means a lot to me to know, even if it’s a small amount. On 23andme I show up, no matter the strength of certainty, as having ~5% Ashkenazim ancestry. I know, I know. It’s a tiny amount. But ALL of my ancestors and their history should be celebrated. I love and cherish them all and would like to just know if this is accurate or not.

    Anyway, I’ve narrowed it down to being from my father’s mother’s side, based on shared family with relatives in the database whom I know personally already and grew up with. My problems however are this:

    1. I am unable to figure out from here how it all works. I know on the markers (I guess? The chromosomes and where the ancestry history is marked) all of my (mainly) Jewish DNA matches had matching segments on those areas and matched (some) with each other on some of those same areas. Some of them had matching surnames. But I’m clueless. I have no clue how to find out how we’re actually related/through whom. Especially when many are in other countries.

    2. My Heritage, when I uploaded the 23andme, didn’t show the Ashkenazim DNA but it showed a genetic group (confusing) related to Ashkenazim DNA as well as Netherlands I think? Majority of surnames listed were very common Jewish surnames, though.

    So anyway, I don’t know if this means I don’t have any Jewish ancestry or not. I know this was a mouthful and hopefully not accidentally offensive somehow, and I know I probably sound silly. Any advice or information is very much appreciated. Thank you so much.

  6. Thanks for your kind reply!
    I will keep searching and hoping for some closer atDNA matches. Twenty years of research so far. Never give up!

  7. My sister and I heard family rumors that we have different fathers. My father is our mother’s husband and her father was rumored to be our mother’s husband’s father. We did our DNA And find we are a 55% match so we must be full siblings. We wonder though, could our DNA match be affected by the fact that both of our fathers would be in the same family, I.e. father and son, if the rumors are true. Or, does a 55% match mean we are definitely full sisters.
    Thank you!

    1. I don’t have the stats for that situation at hand, but I think 54% would be full siblings rather than (half sib + half aunt). There are a couple of way you could tell for sure. If you are both at a site that shows the X chromosome (23andMe, FTDNA, or GEDmatch), and you match all the way across (or almost at GEDmatch … they sometimes miss matching segments), then you share a father. Also, if you both match people who would be related through your father’s mother, then that favors full sibs, too.

  8. Another query re Ancestry: At some point in the tree history the little blue DNA symbol on my ancestors stops, even tho the parents of the relatives ( with the symbol) are found in my tree. Do you know why this happens? ( the person is listed as my 6th GGF but no blue dna symbol) I am trying to post a screen shot but cannot do so.

  9. With incest, how can one tell if my mother’s father is her grand-father or his brother (her great-uncle). Both are dead. The only dna I can see is from the son of the daugther of my mother’s mother. Also, there is DNA from a son and a daugther of the uncle’s two sons.

  10. My mother tested. But she does not know about any of this And I do not have access to her raw data. I have access to my … cousin… who is now not really my cousin. But actually the son of the daughter of my mother’s biological mother’s sister (life was not that complicated a week ago!). He has sent me his raw data. What I hope to be able to do is find out who her biological father is and not have her find out because I have been asked to keep it secret. She does not even know that her mother is not her mother nor that the father she has always believed to be her father isn’t either.

  11. Re: my last answer, the incest is not a conclusion of DNA matches directly. It’s a long story but DNA has confirmed part of the story. I started digging and got an unexpected call asking me to stop. But as I have kids too, I want to know if my great-grand-father is actually my grand-father or it it is one of his brothers. Because it matters to me.

    1. This would be a lot easier to solve with access to your mom’s data. Can you see her matches? How much does she share with your cousin-not-cousin? If you’d like to do a paid consultation to work through this privately, feel free to contact me. https://thednageek.com/contact/

  12. I wonder what the possibilities will be in the future. Will these companies finally add some much needed tools? Will new techniques allow us to pinpoint matches? Would testing more of a persons DNA lead to more precision?

    1. Great questions! The companies continue to improve, so I expect new tools although I can’t predict what they might be. Much of the real innovation, though, comes from the community! New techniques might make things easier, but short of parent–child matches, we’ll always need to do some work on our own to pinpoint matches. (But that’s the fun part, right?) Testing more of our DNA isn’t likely to improve things much for atDNA, except possibly for visual phasing. We already get pretty darned good estimates of shared DNA with what we have. There’s no more mtDNA to test. Testing more Y-DNA can definitely help at deeper levels.

  13. I realize that that GEDmatch Q value algorithm has changed. I don’t understand how a segment with lots of black lines can have a value of >30, yet a good segment with lots of green and >15 cM can have a Q value of 0. Please help me understand what’s going on.

  14. I have a question about consistency between testing companies. I tested at Ancestry and uploaded these results to MyHeritage and FamilyTreeDNA. I have found some autosomal matches with others but the cm match in one example are 11 cm – 1 segment at Ancestry, 26.3 cm – 1 segment at MyHeritage, and 30.54 cm – 1 segment at FamilyTreeDNA. The match has the same tree on all three sites. This seems like a large difference in match results. Does this make sense?

    1. Those differences aren’t particularly large, to be honest. They can be explained by two different things. First, Ancestry down-weights some segments that they think aren’t reflective of genealogical relationships. You can see the amount before the adjustment by clicking on the blue text showing the relationship and cM amount. Second, MyHeritage and FamilyTreeDNA need to make some educated guesses to match uploads to their existing database, and sometimes those educated guesses are overly optimistic. In the grand scheme of things, though, the difference between 11 cM and 31 cM doesn’t affect the interpretation much.

    1. Yes, although it would be easier, cheaper, and ethical to test them using a regular genealogy test with their consent. It’s also likely that the glass would have DNA from other people as well, so you couldn’t be sure the DNA test results were from the two people in question.

  15. thank you for your time but the question is a test to see if the test will know that the two people in the test are not related even though they drank from the same spot on the glass

    1. Again, if you want to know whether they are related, get their explicit consent to test them. To do otherwise would be extremely unethical.

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