DNA Basics Chapter 7: Common Misconceptions about DNA Testing

DNA Basics Chapter 7: Common Misconceptions about DNA Testing


If you’ve been following the DNA Basics blog series, then you already know quite a bit about DNA — from what it is on the molecular level, to how it’s structured, how it’s expressed, and how we test it to tell you where your ancestors were from and help you find new relatives you never knew about.

This month, we want to delve into some common misconceptions about DNA testing.

Myth #1: DNA testing requires spit or blood

Your individual DNA sequence is pretty much the same in almost every cell in your body. That’s very convenient for DNA testing: it means we’re not limited to using the cells in blood or spit. The MyHeritage DNA test is a simple cheek swab. When you gently rub the swab along the inside of your cheek for about 30–60 seconds, epithelial cells are collected on the swab and our lab is able to extract your DNA from those cells.

Myth #2: Because children inherit DNA from their parents, full siblings should get the same results

While it’s true that you inherit 50% of your ethnicities from each parent, you do not necessarily inherit 50% of each of their ethnicities. For example, if your mother is 50% Irish, and 50% Scandinavian, you will not necessarily be 25% Irish and 25% Scandinavian. The ethnic mix you inherit is random. In this example, you might be 10% Irish and 40% Scandinavian. The ethnicities you inherited from your mother should add up to about 50% of your total ethnicity estimate, but there is no way to know within that 50%, how much you have of each of her ethnicities without doing a DNA test.

This is why siblings get different results! Of your mother’s 50% Irish and 50% Scandinavian, she may have passed down 10% Irish and 40% Scandinavian to one child; 20% Irish and 30% Scandinavian to another child.

Myth #3: Your genetic ethnicity estimate will match your known genealogy

There are a number of reasons why your Ethnicity Estimate might not match the ethnicities of the ancestors in your family tree.

If an ethnicity was passed down to you through many generations, you may not have inherited a detectable amount.

You may have inherited unexpected ethnicities from ancestors you never knew about. Even the most robust trees don’t include everyone.

There are also biological limitations to DNA testing like the fact that some populations have similar DNA due to being in close geographic proximity, or to migration patterns that led to mixing of what were previously isolated gene pools. This is why, for example, you might see English when you expected Scandinavian.

Myth #4: All of your ancestors’ ethnicities will appear in your Ethnicity Estimate

While it is true that each generation inherits their ethnicities from the generation before, the amount of each ethnicity that we inherit may vary. For example, if your great-grandfather was part English, he may or may not have passed down all or some of his English ethnicity to his children. Assuming his child — your grandfather — did inherit some English, he may or may not have passed any of it down to his children. Two generations after that, you may or may not have inherited a detectable amount of your great grandfather’s English DNA.

Remember, only half of your ethnicities come from your paternal line and half from your maternal line, which means one quarter of your ethnicities were inherited from each grandparent. The more generations you go back, the less of your DNA can be attributed to each ancestor. Therefore, it is not uncommon to know for a fact that a direct ancestor had a certain ethnicity that does not appear in your Ethnicity Estimate.

If you haven’t done a DNA test, and are curious about how your results will compare to what you expected, you can order a MyHeritage DNA kit or upload DNA data from another company to MyHeritage for free.


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  • Rosemary

    July 12, 2018

    Wow! I love this dna stuff!!

  • Carolyn Butler

    July 13, 2018

    Just curious, my blood type is not either parent, I was told. They are both deceased now. I was interested if this could help me and the mystery?

    • Esther

      July 15, 2018

      Hi Carolyn,

      The autosomal DNA test that we offer will show you an Ethnicity breakdown as well as DNA Matches (matches with other people who you share DNA with).

      Although we do not show blood types in our DNA results, it is possible for you to have a different blood type than that of your parents. For example, two parents with B blood type can produce a child with either B or O blood type, One parent with A and another with B can produce a child with A, B, AB or O blood types, if one parent has A and another has AB, they can either produce a child with A, B or AB blood types.

      Best, Esther / MyHeritage Team

  • Mary Bennett Singletary

    July 13, 2018

    I am wondering more about my Father’s side does your test show where my Mother’s linage AND my Father’s linage comes from?

    • Esther

      July 15, 2018

      Hi Mary,

      The MyHeritage DNA test is an autosomal test, which tests both your maternal and paternal lines.

      Esther / MyHeritage Team

  • Linde Knighton

    July 19, 2018

    That sorta explains why our sister got all the Native genetic markers, while my brother and I got zip. UNFAIR! Because of the BIA, people won’t accept our DNA nonresult, or our genealogy. Plus many Eastern tribes have never been tested. I urge testing of tribes who allow it from Maine to Florida to Mississippi.

  • Philip Hennessy

    August 15, 2018

    Hi, I notice that your article on DNA results is headed ‘DNA Basics Chapter 7: Common Misconceptions about DNA Testing. The Chapter 7 bit pre-supposes that there is perhaps a book or series of articles about DNA. Is it possible to download this, or is it a printed book available on sale somewhere?

    Philip Hennessy

  • Donna Hanna Reed

    August 15, 2018

    I surely would like more tips on my Irish side with Arthur Donnelly. I get MANY tips for the Richardfson
    side….too many really.

  • Ian Forsyth

    August 16, 2018

    thanks for the interesting discussions

  • Gabriel

    August 16, 2018

    Hi as far as I can go back all my ancestors were Italian, my dna came back that I am mostly greek. I am shocked.

  • Michael Parker

    August 16, 2018

    This is very interesting info. Thanks.

  • Al

    August 16, 2018

    Very interesting read…thank you!

  • Sharon Sullivan

    August 17, 2018

    So, if a child’s DNA shows 100% English, it does not mean that both parents are 100% English – though they could be. Each parent would have to be at least 50% English, though. Is that right?
    (And, thanx for this blog, btw -)

    • Esther

      September 4, 2018

      Hi Sharon,

      See our new blog post about this topic:

      Esther / MyHeritage Team

    • Yael

      September 5, 2018

      That’s right, Sharon! A child can inherit any combination of their parents’ ethnicities, so a mom who is 50% English and 50% Scandinavian can pass down an English-Scandinavian combination that is split 20%/30%; 10%/40%, or any other combination that adds up to 50%. If both parents are 50% English, and both parents pass down that 50% to their child, that child will be 100% English, even though the parents are not.

      Thanks for your question,
      Yael/ The MyHeritage team

  • Nancy

    August 19, 2018

    I can easily imagine my genetic makeup as being different from that of my sister. It was apparent in her B blood type, where I have A, Dad has O, and Mom had AB.

    • Yael

      September 4, 2018

      Hi Nancy,

      O is actually recessive, while A and B are co-dominant. It sounds like you and your sister both inherited a recessive O allele from your father, while you inherited the A allele from your mother, and your sister inherited the B allele from your mother. I’ll be posting a new DNA Basics chapter that explains more about this topic, soon. Stay tuned!

      Yael / MyHeritage Team

  • Mary Woodard Overton

    August 19, 2018

    I wasn’t expecting my brother and I to show a few different origins in our results . Thanks for explaining this , but now this presents a huge mystery in tracking down ancestors in thes surprise regions !

  • Ramejkis

    August 20, 2018

    What a surprise, I always knew my family were from Lithuania, but 5% Finnish!

  • Clark Garvin

    August 20, 2018

    I more or less confirmed my ethnicity, however, being adopted I have not gotten any farther.

  • Linde Knighton

    August 30, 2018

    If your blood type doesn’t match your parents, here is one strange situation to think about. I am type O- My sister is type O-. Our brothers are type A. Both Parents Type A. Or were they? Turns out there is a little known blood type called type AO. It doesn’t cause any trouble, but it can confuse people who don’t know about it. If both parents are AO, they can have kids with AO, A or O. That is just weird.

    • Yael

      September 5, 2018

      Hi Linde,

      You’re definitely on to something! O is a recessive blood type while A and B are co-dominant. It sounds like your parents are both AO (heterozyous), so they can each pass down either and A or an O to each of you; you and your sister are OO (homozygous), having inherited an O from both parents; and your brothers are AO (heterozyous), each having inherited an A from one parent and an O from the other. The DNA that you inherit is your genotype, while the trait that is expressed (that you see) is your phenotype. This is a complicated topic that I will break down in the next chapter of DNA Basics. I hope you’ll tune in!

      All the best,
      Yael/ the MyHeritage team

  • Deena Boucher

    October 27, 2018

    I come from a family of eight children. When my dad passed, he NEEDED to tell me of my mothers infidelities. This bothered me. Why did he need to tell me this. Upon his passing, he came to me in a dream and told me, i was not his biological daughter. Hence, i had my DNA tested against my sisters. The test results showed that we are half siblings. Unfortunately, my mother has some psych issues and is also a pathological liar. I cannot get the truth out of her IF she even knows it in her altered mind. I have always been the black sheep of my family. I am close with two of my siblings, my oldest brother who felt like he always needed to protect me and one of my sisters. Family means a lot to me. I quit my job and took care of my dad when he was diagnosed with cancer. He is trying to give me something back but was too late. How do i find out who my biological father is (who may not even know i exist)? I have paid for DNA with Ancestry and 23 and Me. I need help. Can you help me please? I would love to be a part of possibly other siblings lives. I am stuck. Thank you.

    • Esther

      November 5, 2018

      Hi Deena,
      You can upload your results from both those testing services to MyHeritage by going to http://www.myheritage.com/dna/uploads.
      Let us know what you discover.
      Esther / MyHeritage Team

  • Bina

    February 19, 2019

    Also, my sister and I only share 23% of our Dna.

  • Mandy

    December 4, 2019

    Very good information.
    I was born in Brazil, my mom is deceased and I was adopted. Her family is from Portugal. São Miguel Island, on the Azores. I know nothing about my daddy. The 25% of English ethnicity shocked me. Now how do I find out if the English side is really my daddy’s, since mom’s family is Portuguese and Italian? Problem is that I’ve heard that the Y haplogroup cannot be traced on women. This quest been full of excitement anyway. I hope I can find my papa’s family some day.