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.

Concepts – How Your Autosomal DNA Identifies Your Ancestors

Welcome to the concepts articles. This series presents the concepts of genetic genealogy, not the details.  I have written a lot of detailed articles, and I’ve linked to them for those of you who want more.  My suggestion would be to read this article once, entirely, all the way through to understand the concepts with continuity of thought, then go back and reread and click through to other articles if you are interested.

All of autosomal genetic genealogy is based on these concepts of inheritance and matching, so if you don’t understand these, you won’t understand your matches, how they work, why, or how to interpret what they do or don’t tell you.

The Question 

Someone sent me this question about autosomal DNA matching.

“I do not quite understand how the profiles can be identified to an ancestor since that person is not among us to provide DNA material for “testing” and “comparison.”

That’s a really good question, so let’s take a shot at answering this question conceptually.

Do you have a cat or dog?

Chica Pixie Quilt

I bet I could tell if I could see your clothes, your house, your car or your quilt. Why or how?  Because pets shed, and try as you might, it’s almost impossible to get rid of the evidence.  I went to the dentist once and he looked at my sweatshirt and said, “German Shepherd?” I laughed.

When your ancestor had children, he or she shed their DNA, half of it, and it’s still being passed down to their descendants today, at least for the next several generations. Let’s look, conceptually, at how and why this works.

In the following diagram, on the left you can see the generations and the relationships of the people both to the ancestor and to each other.

Our ancestor, John Doe, married a wife, J, and had 2 children. Gender of the children, in this example, does not matter.

Everyone receives one strand of DNA from their mother and one from their father. If you’re interested in more detail about how this works, click here.

In our example below, I’ve divided this portion of John’s DNA into 10 buckets. Think of each of these buckets as having maybe 100 units of John’s DNA.  You can think of pebbles in the bucket if you’d like.  Our DNA is passed, often, in buckets where the group of pebbles sticks together, at least for a while.  Since this is conceptual, our buckets are being passed intact from generation to generation.

John’s mother’s strand of DNA has her buckets labeled MATERNALAB and I’ve colored them pink to make them easy to identify. John’s father’s strand of DNA has his buckets labeled FATHERSIDE and is blue.  Important note – buckets don’t come colored coded pink or blue in nature – you have no idea which side your DNA comes from.  Yes, I know, that’s a cruel joke of Nature.

John married J, call her Jean. Jean also has 2 strands of DNA, one from her mother and one from her father, but in order to simplify things, rather than have two colors for the wives, I’d rather you think of this generationally, so the wives in each generation only have one color. That way you can see the wives’ DNA mixing with the husbands by just looking at the colors. Jean’s color is lavender.

DNA “Shedding” to Descendants

So, now let’s look at how John “sheds” his DNA to his two children and their descendants – and why that matters to us several generations later.

Concept ancestor inheritance

Please note that you can click on any of the graphics to make them larger.

In the examples above, the DNA that is descended in each generational line from John is bolded within the colored square. I also intentionally put it at the beginning and ends of the segments for each child so it’s easy to see.

In the first generation, John’s children each receive one strand of DNA from their mother, J, and one from John. John’s DNA that his children receive is mixed between John’s father’s DNA and John’s mother’s DNA – roughly 50-50 – but not exactly.

At every position, or bucket, during recombination, John’s child will receive either the value in John’s Mom’s bucket or the value at that location in John’s Dad’s bucket.  In other words, the two strands of John’s parent’s DNA, in John, combine to make one strand to give to one of John’s children.  Each time this happens, for each child conceived, the recombination happens differently.

Concept Ancestor inheritance John

In this case, John’s children will receive either the M or the F in bucket one.  In buckets 2 and 3, the values are the same.  This happens in DNA.  The child’s bucket 4 will receive either an E or H.  Bucket 5 an R or E.  Bucket 6 an N or R.  And so forth.  This is how recombination works, and it’s called “random recombination” meaning that we have not been able to discern why or how the values for each location are chosen.

Is recombination really random, like a coin flip?  No, it’s not.  How do we know?  Because clumps of neighboring DNA stick often together, in buckets – in fact we call them “sticky segments.”  Groups of buckets stick together too, sometimes for many generations.  So it’s not entirely random, but we don’t know why.

What we do know for absolutely positively sure is that every person get’s exactly half of their parents’ DNA on chromosomes 1-22.  We are not talking about the X chromosome (meaning chromosome 23) or mitochondrial DNA or Y DNA.  Different topics entirely relative to inheritance.

You can see which buckets received which of John’s parents’ DNA based on the pink and blue color coding and the letters in the buckets.  Jean’s contribution to Child 1 and Child 2 would be mixed between her parents’ DNA too.

Concept Ancestor inheritance child

In the first generation, Child 1 received 6 pink buckets (segments) from John’s mother and 4 blue buckets from John’s father – MATHERSLAB.  Child 2 received 6 blue buckets from John’s father and 4 pink buckets from John’s mother – FATHERALAB.  On the average, each child received half of their grandparents’ DNA, but in reality, neither child received exactly half.

Note that Child 1 and 2 did not necessarily receive the SAME buckets, or segments, from John’s parents, although Child 1 and 2 did receive some buckets with the same letters in them – ATHERLAB.

If you’re thinking, “lies, damned lies and statistics” right about now, and chuckling, or maybe crying, join the club!

Looking at the next generation, John’s Child 1 married K and John’s Child 2 married O.

Child 1

Let’s follow John’s pink and blue DNA in Child 1’s descendants.  Child 1 marries K and had one child.

Concept Ancestor inheritance grandchild child 1 c

John’s grandchild by Child 1 has one strand of DNA from Child 1’s spouse K and one strand from Child 1 which reads MATJJJJLAB. You can see this by K’s entire strand and the grandchild’s other strand, contributed by Child 1, being a mixture of John’s DNA along with his wife J’s DNA.  In this case, for these buckets, John’s mother’s pink DNA is only being passed on.  John’s father’s buckets 4-7 were “washed out” in this generation and the grandchild received grandmother J’s DNA instead.

Concept Ancestor inheritance gen 4 c

In the next generation, 3, John’s grandchild married P and had generation 4, the great-grandchild. Generation 4 of course carries a strand from wife P, but the Doe strand now carries less of John’s original DNA – just MA and LAB at the beginning and end of the grouping.

Concept Ancestor inheritance gen 5 c

In the next generation, 5, the great-great-grandchild, you can see that now John Doe’s inherited DNA is reduced to only the AB at the right end.

Concept Ancestor inheritance gen 6

In the next generation, 6, the great-great-great-grandchild carries only the A, and in the final generation, below, the great-great-great-great-grandchild, none of John Doe’s DNA is carried by that descendant in those particular buckets.

Concept Ancestor inheritance gen 7 c1

Can there be exceptions? Yes.  Buckets are sometimes split and the X chromosome functions differently in male and female inheritance.  But this example is conceptual, remember.

You always receive exactly half of your parents’ DNA, but after that, how much you receive of an ancestor’s DNA isn’t 50% in each generation. You saw that in our examples where both Child 1 and Child 2 inherited a little more or a little less than 50% of each of John’s parents’ DNA.

Sometimes groups of DNA buckets are passed together and sometimes, the entire bucket or group of buckets are replaced by DNA from “the next generation.”

To summarize for Child 1, from John Doe to generation 7, each generation inherited the following buckets from John, with the final generation, 7, having none of John’s DNA at all – at least not in these buckets.

concept child 1

Now, let’s see how the DNA of Child 2 stacks up.

Child 2

You can follow the same sequence with Child 2. In the first generation, Child 2 has one strand of John’s DNA and one of their mother’s, J.

Child 2 marries O, Olive, and their child has one strand from O, and one from Child 2.

Concept Ancestor inheritance gen 3 c 2

Child 2’s contributed strand is comprised of DNA from John Doe and mother J.  You can see that the grandchild has FA and ALAB from John, but the rest is from mother J.

Concept Ancestor inheritance gen 4 c 2

The grandchild (above) married Q and their child generation 4, inherits most of John’s DNA, but did drop the A .

Concept Ancestor inheritance gen 5 c 2

Sometimes the DNA between generations is passed on without recombining or dividing.  That’s what happened in generation 5, above, and 6 below, with John’s DNA.

Concept Ancestor inheritance gen 6 c 2

Generations, 5 (great-great-grandchild) and 6 (great-great-great-grandchild) both receive John’s F and AB, above.

Concept Ancestor inheritance gen 7 c 2

However, in the 7th generation, the great-great-great-great-grandchild only inherits John’s bucket with B.  The F and A were both lost in this generation.

concept child 2

This summary of the inheritance of John’s DNA in Child 2’s descendants shows that in the 7th generation, that individual carries only one of John’s DNA buckets, the rest having been replaced by the DNA of other ancestors during the inheritance recombination process in each generation.

Half the Equation

To answer the question of how we can identify the profile of a person long dead is not answered by this inheritance diagram, at least not directly – because we don’t KNOW how much of John’s DNA we inherited, or which parts.  In fact, that’s what we’re trying to figure out – but first, we had to understand how we inherited DNA from John (or not).

Matching with known family members is what actually identifies John’s DNA and tells us which parts of our DNA, if any, come from John.

Generational Matching

Let’s say I’m in the first cousin generation and I’m comparing my autosomal DNA against my first cousin from this line.  First cousins share common grandparents.

Assuming that they are genetically my first cousin (meaning no adoptions or misattributed parentage,) they are close enough that we can both be expected to carry some of our common ancestor’s DNA. I wrote an in-depth article about first cousin matching here, but for our purposes, we know genetically that first cousins are going to match each other virtually 100% of the time.

Here’s a nice table from the Family Tree DNA Learning Center that tells us what to expect in terms of matching at different relationship levels.

concept generational match

The reason our autosomal DNA matches with our reasonably close relatives is because we share a common ancestor and have inherited at least a bucket, if not more than one bucket, of the same DNA from that ancestor.

That’s the ONLY WAY our DNA could match at the bucket level, given what we know about inheritance. The only way to get our DNA is through our parents who got their DNA through their parents and ancestors.  Now, could we share more than one common ancestral line?  Yes – but that’s beyond conceptual, for now.  And yes, there is identical by chance (IBC), which doesn’t apply to close relatives and in general, nor to larger buckets. If you want to read more about this complex subject, which is far beyond conceptual, click here.

Now, let’s see how we identify our ancestor’s DNA!

Concept ancestor matching

Let’s look at people of the same generation of descendants and see how they match each other.  In other words, now we’re going to read left to right across rows, to compare the descendants of child 1 and 2.  Previously, we were reading up and down columns where we tracked how DNA was inherited.

Bolded letters in buckets indicate buckets inherited from John, just like before, but buckets with black borders indicate buckets shared with a cousin from John’s other child.  In other words, a black border means the DNA of those two people match at that location.  Let’s look at the grandchildren of John compared to each other.  John’s grandchildren are first cousins to each other.

Concept ancestor matching 1c

Our first cousins match on 4 different buckets of John’s DNA: A, L, A and B.  In this case, you can see that both individuals inherited some DNA from John that they don’t share with each other, such as their first letters, M for Child 1 and F for child 2.  Because they inherited different pieces from John, because he inherited those pieces from different ancestors, the first cousins don’t match each other on that particular bucket because the letters in their individual buckets are different.

Yes, the first cousins also match on wife J’s DNA, but we’re just talking about John’s DNA here.  Now, let’s look at the next generation.

Concept ancestor matching 2c

Our second cousins, above, match on four buckets of John’s DNA.  Yes, the A bucket was inherited from John’s Mom in one case, and John’s Dad in the other case, but because the letter in the bucket is the same, when matching, we can’t tell them apart.  We only “know” which side they came from, in this case, because I told you and colored the buckets pink and blue to illustrate inheritance.  All the actual software matching comparison has to go by is the letter in the bucket.  Software doesn’t have the luxury of “knowing” because in nature there is no pink and blue color coding.

concept ancestor matching 3c

Our third cousins, above, match, but share only A and B, half as much of John’s DNA as the second cousins shared with each other.

Concept ancestor matching 4c

Our 4th cousins, above, are lucky and do match, although they share only one bucket, A, of John’s DNA, which happens to have come from John’s mother.

Concept ancestor matching 5c

By the time you get down to the 5th cousins, meaning the 7th generation, the cousins’ luck has run out, because these two 5th cousins don’t match on any of John’s DNA.

Most 5th cousins don’t match and few 6th cousins match, at least not at the default thresholds used by the testing companies – but some do.  Remember, we’re dealing with matching predictions based on averages, and actual individual DNA inheritance varies quite a bit.  Lies, damned lies and statistics again!

You can adjust your own thresholds at GedMatch, in essence making the buckets smaller, so increasing the odds that the contents of the buckets will match each other, but also increasing the chances that the matches will be by chance.  Again, beyond conceptual.

concept buckets inherited

While this is how matching worked for these comparisons of descendants, it will work differently for every pair of people who are compared against each other, because they will have, or not have, inherited different (or the same) buckets of DNA from their common ancestor.  That’s a long way of saying, “your mileage will vary.”  These are concepts and guidelines, not gospel.

Now, let’s put these guidelines to work.

Matching People at Testing Companies

Ok, so now let’s say that I match Sarah Doe. I don’t know Sarah, but we are predicted to be in the 2nd or 3rd cousin range, based on the amount of our DNA that we share.

As we know, based on our inheritance example, amounts of shared DNA can vary, but we may well be able to discern a common ancestor by looking at our pedigree charts.

Sure enough, given her surname as a hint, we determined that John Doe is our common ancestor.

That’s great evidence that this DNA was passed from John to both of us, but to prove it takes a third person matching us on the same segment, also with proven descent from John Doe. Why?  Because Sarah and I might also have a second common genealogical line, maybe even one we don’t know about, that’s isn’t on our pedigree chart. And yes, that happens far more than you’d think. To prove that Sarah Doe and my shared DNA is actually from John Doe or his wife, we need a third confirmed pedigree and DNA match on that same bucket.

A Circle is Not a Bucket

If you just said to yourself, “but Ancestry doesn’t show me buckets,” you’re right – and a Circle is not a bucketA Circle means you match someone’s DNA and have a common tree ancestor.  It doesn’t mean that you or any Circle members match each other on the same buckets. A bucket, or segment information, tells you if you match on common buckets, which buckets, and exactly where.  You could match all those people in a Circle on different buckets, from completely different ancestors, and there is no way to know without bucket information.  If you want to read more about the effects of lack of tools at Ancestry, click here and here.

Proof

Matching multiple people on the same buckets who descend from the same ancestor through different children is proof – and it’s the only proof except for very close relatives, like siblings, grandparents, first cousins, etc.  Circles are hints, good hints, but far, far from proof.  For buckets, you’ll need to transfer your Ancestry results to Family Tree DNA or to GedMatch, or preferably, both.

I’m most comfortable if at least two of the individuals of a minimum of three who match on the same buckets and share an ancestor, which is called a triangulation group, descend from at least two different children of John.  In other words, the first common ancestor of the matches is John and his wife, not their children.

Cross generational matches 2

The reason I like the different children aspect is because it removes the possibility that people are really matching on the downstream wives DNA, and not John’s.  In other words, if you have two people who match on the same buckets, A and B above, who both descend from John’s Child 1 who married K, they also will share K’s DNA in addition to John’s.  So their match to each other on a given bucket might be though K’s side and not through John’s line at all.

Let’s say A and B have a match to unknown person D who is adopted and doesn’t know their pedigree chart.  We can’t make the presumption that D’s match to A and B is through John Doe and Jean, because it might be through K.

However, a match on the same buckets to a third person, C, who descends through John’s other child, Child 2, assuming that Child 2 did not also marry into K’s (or any other common) line, assures that the shared DNA of A and B (and C) in that bucket is through John or his wife – and therefore D’s match to A, B and C on that bucket is also through the same common ancestor.

If you want to read more about triangulation, click here.

In Summary

The beauty of autosomal DNA is that we carry some readily measurable portion of each of our ancestors, at least the ones in the past several generations, in us. The way we identify that DNA and assign it to that ancestor is through matching to other people on the same segments (buckets) that also descend from the same ancestor or ancestral line, preferably through different children.  In many cases, after time, you’ll have a lot more than 3 people descended from that ancestral line matching on that same bucket.  Your triangulation group will grow to many – all connected by the umbilical lifethread of your common ancestors’ DNA.

As you can see, the concepts, taken one step at a time are pretty simple, but the layers of things that you need to think about can get complex quickly.

I’ll tell you though, this is the most interesting puzzle you’ll ever work on!  It’s just that there’s no picture on the box lid.  Instead, it’s incredible real-life journey to the frontiers inside of you to discover your ancestors and their history:)  Your ancestors are waiting for you, although my ancestors have a perverse sense of humor and we play hide and seek from time to time!