People who test at Family Tree DNA and receive mitochondrial DNA full sequence results often have questions about how they can use their results to further their understanding of their ancestors.
One of the things you can do is to build a mitochondrial DNA haplotree of your own, showing how various people that you match are or are not descended from common ancestors. To do this, you’ll need to contact your matches and share your mutations.
Your results at Family Tree DNA tell you how many mutations you have, shown below, in the genetic distance column. For more information on genetic distance, how it is calculated and what it means, click here.
Your results at MitoSearch, if you upload, or within projects at Family Tree DNA, show you the HVR1+HVR2 region mutations, but the only way to compare the coding region, or full sequence matches is for the people involved to share them directly with each other.
How can mutations help identify your common ancestors with your matches, or if not the ancestor themselves, at least where they were from?
Let’s look at reconstructing a DNA tree based on both your common mutations and mutations you don’t share with your matches.
When building a DNA tree, remember that once a mutation enters the mitochondrial DNA, unless there is a back-mutation, which is exceedingly rare, that mutation will be found in all descendants.
This discussion excludes heteroplasmic mutations, which can be easily identified as any mutation that ends with any letter other than T, A, C or G – for example 16519Y would be heteroplasmic, indicated by the Y. The simple explanation for heteroplamic mutations is that they are a mutation in progress, and therefore relatively recent. They don’t pertain to deeper ancestry, so we are ignoring them for this discussion. Most people don’t have heteroplasmic mutations.
Building Your Tree
Let’s look at an example of how to build a mitochondrial mutation tree.
A common ancestor, at the top of the tree, has 2 mutations that they pass to all of their descendants.
Ancestor B and C have those 2 mutations, so they match ancestor A and each other.
Both ancestor B and C have both developed mutations that don’t match each other. In real life, it would be very rare for mitochondrial DNA to develop mutations in every generation, so just view this as a rather time-compressed example.
In ancestor B’s line, there are two contemporary individuals, D and E, who have all 3 of the mutations that Ancestor B carried.
So, you have a tree that looks like this. You can click to enlarge.
Ancestor C also has two descendants, F and G, who both carry all of Ancestor C’s mutations, plus both F and G each have a mutation that doesn’t match each other.
So, now let’s say Person I comes along as a match. You can tell which line they belong to, and which lines they don’t, by which mutation(s) person I carries, as compared to your tree. For example, if person I carries mutations 1, 2 and 4, then you know that they are a descendant of Ancestor C, not B. If they carry 1, 2, 4 and 5, then they descend from Person G’s line.
I suggest that you work with your full sequence matches to build this type of mitochondrial descendancy tree. You must work with your matches, because you cannot see your matches’ coding region results, not even in projects, so you’ll have to ask each one to share with you. Be prepared, some people won’t answer, but often, based on who the people match that do respond to you, and are willing to share, you can figure out the missing blanks.
For example, Let’s say John matches you with one mutation, and so does Joe, but Joe doesn’t answer your e-mail. However, John wants to work with you and John matches Joe exactly. Now you know which mutation Joe has as well – the same one as John.
You know that each of your full sequence matches is within a maximum of 3 mutations difference from you, because that’s the maximum that Family Tree DNA allows to be considered a match at the full sequence level.
Of course, not all of your matches will have the same 3 mutations, which is why you’ll need to work with them to see how your tree fleshes out. Who knows what surprises you may find.
The first question I ask each of my matches, after explaining what I’m trying to do, is whether they share any of my extra or missing mutations, with the exception of the insertions at 309, 315 or 522 and/or any mutation at 16519. These mutations are extremely common. Sometimes people are more comfortable sharing specific mutations than sending you their results. Other people will be glad to send results. In rare instances, the coding region may hold mutations that have medical significance, which is why Family Tree DNA doesn’t show specific mutations, only whether you match or not.
In the example above, you can see that C16189T is normally present in this mitochondrial sequence, but it missing from this person’s results.
Your mitochondrial tree that you build may well shed light on your common ancestor and based on the location of the oldest ancestor of the person at the top of your tree, may also shed light on the location where your common ancestor may have lived and the migration path she took to where your most distant ancestor in this line was found.
My own mitochondrial DNA tree begins in Scandinavia and only my line winds up in Germany before 1700. Another branch is found in Poland.
Ironically, my exact matches are in Norway (red), not to the line in Poland (orange). The rest of the lines whom I match and that also descend from my Scandinavian ancestor are still found in Scandinavia with one exception found in southern Russia which could be a result of migration to this region from the Germanic region of Europe in the 1700s and 1800s. This tells me that I’m closer, genetically, to the Scandinavian branches than the Polish branch, which is not at all what I would have expected. The Polish branch apparently migrated separately from mine.
My mitochondrial tree also tells me that the common ancestor of all of the matches likely originated in Scandinavia, possibly Norway, also not something I would have expected, given that my most distant ancestor is very clearly German, based on church records.
Give building your mitochondrial tree a try and see what kinds of surprises it may hold! If you haven’t yet tested your full sequence mitochondrial DNA, order that test today. You have ancestors waiting for you!
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