Concepts – Percentage of Ancestors’ DNA

A very common question is, “How much DNA of an ancestor do I carry and how does that affect my ethnicity results?”

This question is particularly relevant for people who are seeking evidence of a particular ethnicity of an ancestor several generations back in time. I see this issue raise its head consistently when people take an ethnicity test and expect that their “full blood” Native American great-great-grandmother will show up in their results.

Let’s take a look at how DNA inheritance works – and why they might – or might not find the Native DNA they seek, assuming that great-great-grandma actually was Native.

Inheritance

Every child inherits exactly 50% of their autosomal DNA from each parent (except for the X chromosome in males.) However, and this is a really important however, the child does NOT inherit exactly half of the DNA of each ancestor who lived before the parents. How can this be, you ask?

Let’s step through this logically.

The number of ancestors you have doubles in each generation, going back in time.

This chart provides a summary of how many ancestors you have in each generation, an approximate year they were born using a 25 year generation and a 30 year generation, respectively, and how much of their DNA, on average, you could expect to carry, today. You’ll notice that by the time you’re in the 7th generation, you can be expected, on average, to carry 0.78% meaning less than 1% of that GGGGG-grandparent’s DNA.

Looking at the chart, you can see that you reach the 1% level at about the 6th generation with an ancestor probably born in the late 1700s or early 1800s.

It’s also worth noting here that generations can be counted differently. In some instances, you are counted as generation one, so your GGGGG-grandparent would be generation 8.

In general, DNA showing ethnicity below about 5% is viewed as somewhat questionable and below 2% is often considered to be “noise.” Clearly, that isn’t always the case, especially if you are dealing with continental level breakdowns, as opposed to within Europe, for example. Intra-continental (regional) ethnicity breakdowns are particularly difficult and unreliable, but continental level differences are easier to discern and are considered to be more reliable, comparatively.

If you want to learn more about how ethnicity calculations are derived and what they mean, please read the article Ethnicity Testing – A Conundrum.

On Average May Not Mean You

On average, each child receives half of the DNA of each ancestor from their parent.

The words “on average” are crucial to this discussion, because the average assumes that in fact each generation between your GGGGG-grandmother and you inherited exactly half of the DNA in each generation from their parent that was contributed by that GGGGG-grandmother.

Unfortunately, while averages are all that we have to work with, that’s not always how ancestral DNA is passed in each generation.

Let’s say that your GGGGG-grandmother was indeed full Native, meaning no admixture at all.

You can click to enlarge images.

Using the chart above, you can see that your GGGGG-grandmother was full native on all 20 “pieces” or segments of DNA used for this illustration. Those segments are colored red. The other 10 segments, with no color, were contributed by the father.

Let’s say she married a person who was not Native, and in every generation since, there were no additional Native ancestors.

Her child, generation 6, inherited exactly 50% of her DNA, shown in red – meaning 10 segments..

Generation 5, her grandchild, inherited exactly half of her DNA that was carried by the parent, shown in red – meaning 5 segments..

However, in the next generation, generation 4, that child inherited more than half of the Native DNA from their parent. They inherited half of their parent’s DNA, but the half that was randomly received included 3 Native segments out of a possible 5 Native segments that the parent carried.

In generation 3, that child inherited 2 of the possible 3 segments that their parent carried.

In generation 2, that person inherited all of the Native DNA that their parent carried.

In generation 1, your parent inherited half of the DNA that their parent carried, meaning one of 2 segments of Native DNA carried by your grandparent.

And you will either receive all of that one segment, part of that one segment, or none of that one segment.

In the case of our example, you did not inherit that segment, which is why you show no Native admixture, even though your GGGGG-grandmother was indeed fully Native..

Of course, even if you had inherited that Native segment, and that segment isn’t something the population reference models recognize as “Native,” you still won’t show as carrying any Native at all. It could also be that if you had inherited the red segment, it would have been too small and been interpreted as noise.

The “Received” column at the right shows how much of the ancestral DNA the current generation received from their parent.

The “% of Original” column shows how the percentage of GGGGG-grandmother’s DNA is reduced in each generation.

The “Expected” column shows how much DNA, “on average” we would expect to see in each generation, as compared to the “% of Original” which is how much they actually carry.

I intentionally made the chart, above, reflect a scenario close to what we could expect, on average. However, it’s certainly within the realm of possibility to see something like the following scenario, as well.

In the second example, above, neither you nor your parent or grandparent inherited any of the Native segments.

It’s also possible to see a third example, below, where 4 generations in a row, including you, inherited the full amount of Native DNA segments carried by the GG-grandparent.

Testing Other Relatives

Every child of every couple inherits different DNA from their parents. The 50% of their parents’ DNA that they inherit is not all the same. The three example charts above could easily represent three children of the GG-Grandparent and their descendants.

The pedigree chart below shows the three different examples, above.  The great-great-grandparent in the 4th generation who inherited 3 Native DNA segments is shown first, then the inheritance of the Native segments through all 3 children to the current generation.

Therefore, you may not have inherited the red segment of GGGGG-grandmother’s Native DNA, but your sibling might, or vice versa. As you can see in the chart above, one of your third cousins received 3 native segments from GGGGG-grandmother. but your other third cousin received none.

You can see why people are always encouraged to test their parents and grandparents as well as siblings. You never know where your ancestor’s DNA will turn up, and each person will carry a different amount, and different segments of DNA from your common ancestors.

In other words, your great-aunt and great-uncle’s DNA is every bit as important to you as your own grandparent’s DNA – so test everyone in older generations while you can, and their children if they are no longer available.

Back to Great-Great-Grandma

Going back to great-great-grandma and her Native heritage. You may not show Native ethnicity when you expected to see Native, but you may have other resources and recourses. Don’t give up!

Reason Resources and Comments
She really wasn’t Native. Genealogical research will help and mitochondrial DNA testing of an appropriate descendant will point the way to her true ethnic heritage, at least on her mother’s side.
She was Native, but the ethnicity test doesn’t show that I am. Test relatives and find someone descended from her through all females to take a mitochondrial test. The mitochondrial test will answer the question for her matrilineal line unquestionably.
She was partly, but not fully Native. This would mean that she had less Native DNA than you thought, which would mean the percentage coming to you is lower on average than anticipated. Mitochondrial DNA testing someone descended from her through all females to the current generation, which can be male, would reveal whether her mother was Native from her mother’s line.
She was Native, but several generations back in time. You or your siblings may show small percentages of Native or other locations considered to be a component of Native admixture in the absence of any other logical explanation for their presence, such as Siberian or Eastern Asian.

Using Y and Mitochondrial DNA Testing to Supplement Ethnicity Testing

When in doubt about ethnicity results, find an appropriately descended person to take a Y DNA test (males only, for direct paternal lineage) or a mitochondrial DNA test, for direct matrilineal results. These tests will yield haplogroup information and haplogroups are associated with specific world regions and ethnicities, providing a more definitive answer regarding the heritage of that specific line.

Y DNA reflects the direct male line, shown in blue above, and mitochondrial DNA reflects the direct matrilineal line, shown in red. Only males carry Y DNA, but both genders carry mitochondrial DNA.

For a short article about the different kinds of DNA and how they can help genealogists, please read 4 Kinds of DNA for Genetic Genealogy.

Ethnicity testing is available from any of the 3 major vendors, meaning Family Tree DNA, Ancestry or 23andMe. Base haplogroups are provided with 23andMe results, but detailed testing for Y and mitochondrial DNA is only available from Family Tree DNA.

To read about the difference between the two types of testing utilized for deriving haplogroups between 23andMe and Family Tree DNA, please read Haplogroup Comparisons between Family Tree DNA and 23andMe.

For more information on haplogroups, please read What is a Haplogroup?

For a discussion about testing family members, please read Concepts – Why DNA Testing the Oldest Family Members is Critically Important.

If you’d like to read a more detailed explanation of how inheritance works, please read Concepts – How Your Autosomal DNA Identifies Your Ancestors.

16 thoughts on “Concepts – Percentage of Ancestors’ DNA

  1. Roberta, I enjoyed this article, but will have to read more carefully to digest its meaning. I just ordered a full sequence MtDNA test for my wife, age 43. Her mother was a Fairweather (maiden mame), whose mother was a Vautier, whose mother was a Vollmer. My sister also did a full sequence MtDNA test a few years ago. I have the results but have not studied enough and do not know enough to derive any significant benefit or understanding of the results. We are virtually positive our mother had Native American DNA. She was a Qualls (maiden name), whose mother was a Brown (maiden name), whose mother was a Harbert ( maiden name), whose mother was a Tinney (maiden name). I have photos of all these women except for Annie Vollmer, my wife’s great grandmother. The photos of Martha Ellen (Harbert) Brown and her mother Savannah (Tinney) Harbert (married to Joe Bailey Harbert) are, in my opinion, unmistakably, reflective of definitive Native American physiological traits. I will be happy to provide all results of my sister’s FTDNA test and all photos and other hard data. I have been a huge supporter of FTNA going back at least ten years and have referred innumerable customers to them. I have tested at 111 markers (Y-DNA, Bryan Surname Project)) and have a few very good and valuable matches. I have also tested for L- 226 (Irish Tyoe 3, O’Brien; County Clare). i have referred many customers to FTDNA (Bryan, McDaniel, Qualls surname projects). My maternal grandmother was Josephine (Brown) Qualls. She married Hugh Benton Qualls, son of John Yell Qualls, son of Martin Qualls. Josephine, her mother Martha Ellen Harbert Brown, and Martha’s mother Savannah (Tinney) Harbert all are believed to be of Chickasaw Indian heritage. None of them registered on the Dawe’s Roll, so we have to rely on DNA, pictures, and family lore and tradition. Would you be willing to help me in the analysis and interpretation of my sister’s MtDNA results?

  2. Averages are not all that we have to work with. We know a lot about the variability in inheritance and the probaility of inheriting nothing from a particular ancestor. Graham Coop has written about the variable amount
    https://gcbias.org/2013/11/04/how-much-of-your-genome-do-you-inherit-from-a-particular-ancestor/
    and how many of your ancestors are genetic ancestors as well as genealogical ones
    https://gcbias.org/2013/11/11/how-does-your-number-of-genetic-ancestors-grow-back-over-time/

  3. I have one percent Western African according to ftdna(this showed up even before they started including trace amounts). I am still wondering if this could be from very far back or should I expect it to be from a 4th great grandparent. I have a couple of people I am trying to verify in my tree. I am not sure if I have the right people in the census (they did not stay in one location/rented farms), but a man I think may be my 3rd great grandfather is listed as mulatto(not his wife or children, though) in the 1850 census. If I have the right guy, and his correct parents, his mother and father but not all of his sibling are listed as mulatto in previous censuses back to 1830. I am not sure if this is possible, probable, or unlikely with me having 1% African dna. I would really like to see possible shared dna projections for people with mulatto ancestry (since there may have been intermarrying with others of mixed race for some generations).

  4. A few of my family show a tiny bit of Indian ancestry in our autosomal DNA. Like many families there is a story that we have an Indian ancestor. I recently found my great-great-grandfather in a list of colored volunteers in the Civil War in the Union Army. The list describes him as having dark eyes, dark hair and dark complexion. He is listed on a census as white. The military unit he was in was not an African American unit. Does the term *colored* include those of American Indian ancestry ? What could possibly be the reason for making a list of soldiers that were not purely of European descent ?

    • Colored means different things in different contexts, but generally, in that time and place, it means “not white.” Discrimination was rampant at that time and non-white soldiers had to serve in “colored troops.” What you can discern from that is that her wasn’t entirely white, but he could pass for white (census.) Have you ordered his military records from NARA?

      • I got his military and pension records many years ago. There was no mention of any mixed ancestry.
        My great-great-grandfather’s mother was German, the step-grandmother was a Goins, descended from the known early slave Gowens/Goings/etc. The bio-grandmother was Asinor Wells, that I have never been able to trace with any assurance. The name, Asinor, is unusual.
        And the generation previous to that, my gr.gr.grandfather’s gr.grandfather, was a transported convict 1735, released in Baltimore Co., MD in 1742,who married Jane Green in 1744, that I never could trace. The status of a convict certainly limited his associations during his 7 year tenure and then whom he could marry when freed. They moved to the Virginia frontier by 1750, where I imagine the qualities of character trumped a checkered past or ethnic prejudice. He served in the French and Indian war, and sons all served in the Rev. War. The entire family moved to KY after the War.
        I don’t have a picture of my gr.gr.grandfather, but do have one of his son, my great-grandfather. I don’t see any trace of African in his face but can imagine Indian. His son, my great-uncle, looked very Indian to me, and in the summer was extremely dark. He also had almost no facial hair.
        Our family has a physical characteristict common to NE Asians, an apparent lack of apocrine glands, but do not have the dry ear wax.

  5. My grandfather was one of three brothers who married three sisters from another family, and we have DNA results from descendants. My dad’s cousin’s daughter shows up closer related to me than she would normally, as I expected. Many other people in past were doubly related to me, and not as close cousins marrying, but as relatives marrying. I also have several double ancestors from back five generations or more . I would think this would probably make matches appear closer in time, or reinforce DNA that might have faded out in autosomal DNA tests. Would you please make a comment on this, and maybe show a way to chart this.

    • Yes, they appear closer in time. That’s called pedigree collapse and you just have to do the math with the fractions. I can’t think of an easy way to display this because everyone’s situation is different. I feel for you Rosemary – this makes everything more complex. As for autosomal, it would be less likely to wash out if you could potentially inherit that segment from two sources. This is the same principle as identical by population – and now you understand how those populations came to carry so much of the same DNA:)

      • I am probably a lot like my ancestors. Math fractions frives me batty. I will go for close approximations.

  6. My grandfather was one of three brothers who married three sisters from another family, and we have DNA results from descendants. My dad’s cousin’s daughter shows up closer related to me than she would normally, as I expected. Many other people in past were doubly related to me, Would you please make a comment on this, and maybe show a way to chart this.

    • Ooops – Something happened with the message posting and this above posted twice., and something I was writing concerning Qualls disappeared completely. Grrrr. I have a couple of exact Mt-DNA matches to Qualls, although my Mt-DNA is western European. I have met a Qualls who appeared 100% Native American. My husband’s aunt married a Qualls descendant as her 2nd husband (no children). One of these researched DNA matching Qualls lines is buried in a Sanders Cemetery in northern Arkansas. What I have is on my tree is at Ancestry.com., where there is also Brown and Bryan / Bryant, but unknown if those lines are related to Qualls.

      I own a book, “Social Anthropology of North American Tribes,” by Fred Eggan, . U. of Chicago Press, that discusses marrying traditions within tribes. The thing that caught my eye is the claim that old clan marrying practices are the last to die out of the old traditions. This is interesting related to both DNA and genealogy.

  7. Roberta, thank-you so much for these educational posts!
    Before my father died, he tested through ancestry, and I’ve transferred his data to Family Tree DNA. Is it possible to upgrade his results (for mitochondrial DNA) from that original data?

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