Does DNA testing show both maternal and paternal ancestry?

Question

Would my sister and I get the same results being I am a brother. Same parents for both of us.

---

I wasn't sure how to ask the question. What I am wondering if the results would show the same geographic locations of where our ancestors came from. I was told that hers would show maternal location mine would show paternal. I'm not sure if that makes sense.

We have done genealogy on both sides of our family. Our father's family comes from Denmark and we have gone back as far as we can to the 1600's. Our mothers family comes from England and Scotland and we have gone to the early 1700's on that side.

My sister said we should do the DNA test advertised on TV by Ancestry. I thought we would get the same results. She thinks that she would get only information from the maternal side, and I would have to do it to get paternal information.

I am the only living male of our sibling group. I don't see a real need to do the test; she has a different opinion.

Answer 1

There are three sorts of DNA:

• Autosomal DNA. Each child inherits 50% of their autosomal DNA (atDNA) from each parent at random, so 2 full siblings would have an approximately 50% overlap between themselves -- not 100% because of the random nature of inheritance.

• mtDNA. Each child inherits their mtDNA (almost always unchanged) from the mother, so two maternal siblings would have identical mtDNA. Ony daughters pass on the mtDNA that they received to their children.

• Y-DNA. Every son inherits their Y-DNA from their father (perhaps with some mutations) and passes it on to their sons. Daughers do not receive Y-DNA and so cannot pass it on.

With this in mind:

• Both you and your sister will have identical mtDNA, which will point back to where your maternal line (mother's mother's mother's etc.) came from in the very distant past. It's not very useful for genealogy because it changes so little, so any 'matches' will be so far back you have zero chance of tracing the linkage. It's also not very useful for knowing where your ancestors came from, again because of how far back it goes.

• Only you will have Y-DNA, which will point back along your paternal line (father's father's father's etc.). This is more useful for genealogical purposes as it can reveal a shared ancestor with others who have tested within so-called genealogical timeframes (i.e. the period with which you should be able to ties the DNA results up with documentary evidence), but it still only looks at one small part of the picture of where you came from.

• Both of you will have inherited different but overlapping atDNA. atDNA is the most useful for identifying people who share ancestors with you within a genealogical timeframe, but be aware that it can be a lot of work identifying exactly where those matches lie in your tree.

• In addition, the company that you test with will compare your atDNA with the atDNA of everyone else who has tested with them, and use this to assign a mix of ethnicities (a% this b% that c% the other...). These estimates are only as good as the information about their origins provided by the people who have already tested, and the volume of people who have tested with roots in each region, so take them with a pinch of salt -- and be aware that you and your sister might show up with different ethnicities because of the random nature of inheritance -- she could show up as predominantly of Danish roots, and you as predominantly Scottish for example.

There's an excellent article on this at the International Society of Genetic Genealogy website.

Answer 2

it is definitely possible for two siblings to get pretty different ancestry results from a DNA test. Even when they share the same parents. DNA isn't passed down from generation to generation in a single block. Not every child gets the same 50% of mom's DNA and 50% of dad's DNA.

For a entertaining discussion of this see: Who’s More Irish, You or Your Sibling? The Surprising Science Behind the Inheritance of Ethnicity by — Anna Swayne on the Ancestry blog (undated).

Lastly, it depends on what you mean by "same" (results, not parents).

Answer 3

Building on this answer:

be aware that you and your sister might show up with different ethnicities because of the random nature of inheritance -- she could show up as predominantly of Danish roots, and you as predominantly Scottish for example.

You should also be aware that the same person can show up with different ethnicity estimates if they test with different companies.

Judy G. Russell has discussed ethnicity estimates several times on her blog The Legal Genealogist -- one recent post in the series is "Still Not Soup". (The titles refer to an American TV commercial whose tag line was "Is it soup yet?")

Her posts explain the process of how the ethnicity estimates are made in plain, non-technical language:

[T]hey take the DNA of living people — us, the test takers — and they compare it to the DNA of other living people — people whose parents and grandparents and, sometimes, even great grandparents all come from one geographic area. Then they try to extrapolate backwards into time.

In other words, if your test comes back saying you have ancestors from Denmark, that is because the test company is comparing your results to a set of people whose family are known to have come from there during the timeframe used by the testing company -- that set of people is sometimes called a reference population or a reference panel.

AncestryDNA is notorious when starting out for having had problems with over-reporting that people had Scandinavian ethnicity. The tests are being refined but in my opinion, the ethnicity estimates are mostly useful for very technical users who can read the white papers and know the nuances of the test kits and reference populations which are being used. In her post "Ethnicity Testing – A Conundrum" from 10 Feb 2016, Roberta Estes says on her blog DNA Explained:

Today, about 50% of the people taking autosomal DNA tests purchase them for the ethnicity results. Ironically, that’s the least reliable aspect of DNA testing – but apparently somebody’s ad campaigns have been very effective. After all, humans are curious creatures and inquiring minds want to know. Who am I anyway?

She also says that:

Ancestry continues to have “a Scandinavian problem” where many/most of their clients have a significant amount (some as high as the 30% range) of Scandinavian ancestry assigned to them that is not reflected by other testing companies or tools, or the tester’s known heritage – and is apparently incorrect.

My advice to all people considering DNA testing is to:

• Understand that you may learn things you weren't expecting (e.g. that somewhere in your family tree, you may discover unexpected bio-parents -- sometimes called NPE for 'Non-Parental Events', which I prefer to parse as 'Not the Parent Expected').
• Have a clear idea of what you want to learn from DNA testing.
• Educate yourselves about what the tests can tell you, so you know whether the test you are considering will give you the information you want to know.
• Understand that ethnicity estimates are only estimates and the process used by company A may not be the process used by company B -- and those processes are changing all the time.

Resources:

• Ancestry Blog: Determining Your DNA Ethnicity Estimate
• AncestryDNA Ethnicity White paper
• AncestryDNA Matching White paper