Mirror Trees (For the Genealogically Challenged)

I’m finally getting around to explaining the whole concept of mirror trees…I am aiming to explain it in a way that will be understood by those who aren’t necessarily into genealogy, as I have mentioned it so many times to family members and friends when they ask how I’m going with the search for Mum’s Dad…without fail I am greeted with blank stares and more questions (“What’s a mirror tree?”) every time!! I’ll try my best to keep this as user friendly as possible! This is a topic talked about fairly often, so you will see a list of links to articles/videos at the bottom of this post that I myself have perused over the last few months.

ANYWAY, here goes.

Basically put, a mirror tree is a replica of a DNA match’s tree. This is a technique used often by adoptees searching for their parents and other close relatives and can only be used on the Ancestry platform.

Why only Ancestry, you ask? 

When you administer a DNA test with Ancestry and receive your results, you will see a page like this:

Screen Shot 2017-07-26 at 6.15.22 pm

There are two aspects of this DNA homepage to make note of. First, take a look at the line at the top of the page, under “Hello Emily” that says “This test is shown to matches as Emily. Linked to Emily“. And secondly, note the middle column on this page, where it says “6 Shared Ancestor Hints“. Both of these features are important.

Ancestry allows you to attach your DNA to your profile within the family tree you have built on the website. So in my case, I’ve attached my DNA sample to the bottom of the family tree I’ve created on Ancestry, the profile that says “Emily”. Ancestry has formulated this helpful algorithm that can help you find common ancestors between you and your DNA matches, known as “Shared Ancestor Hints” or “SAHs”. This only works if:

a. You have a reasonably sized tree.

b. You have linked your DNA to your tree.

c. Your DNA matches also have a reasonably sized tree AND have also linked their own DNA to their trees!

But essentially, what happens is that the algorithm compares your DNA match’s tree to yours, if you both happen to have the same direct ancestor in your trees, it will then calculate what your relationship is to that particular DNA match, with the shared ancestor in mind. When you click on the “Shared Ancestor Hints” section, and you click on one of the DNA matches in the list, this is what shows up:

Screen Shot 2017-07-27 at 12.43.35 am

This particular Shared Ancestor Hint of mine has proven a 5th cousin DNA match! Ancestry’s system is really helpful where this is concerned, it will help you do the work, if you provide them with the means to do so. BUT, that is a topic for another time! Back to the point. Hope everyone is still managing to stay with me so far!!


These two aspects are important when creating a mirror tree, along with a close DNA match (usually no more distant than 2nd cousins!) who either has a tree or is nice enough to provide you with enough information via email, etc to begin the tree.

In my case, I used an estimated 2nd cousin match from my Mum’s DNA kit (K, who is mentioned in previous posts) If K is an estimated second cousin, she and Mum would share a set of great grandparents. But which set? We only know of two sets of great grandparents, and they are on the biological maternal side. K doesn’t match our known maternal DNA matches, so she must be a paternal relative somehow.

This is where using a mirror tree comes in.

I created a new tree, (and made the damn thing private, it’s probably the only instance I’d advocate for private trees), and made K the “home person”. That is, the person from which I’d build the tree. K was easygoing from the very start and provided me with the information that I wouldn’t necessarily find in the Ancestry records (re: the names of her parents) and grandparents.

This was enough for me to go on for the time being and with the help of lovely Rose, we built the tree out as far as we could for K’s family on both sides. Sticking with the bare bones at that point, we only followed direct ancestor couples back within this tree and went back later in filled in the family groups as best we could afterwards.

Once we had a decent tree together, it was time to attach Mum’s DNA to K’s profile in that tree.

In doing so, we were looking for those Shared Ancestor Hints, which would highlight which side of K’s family Mum fits into and also give us some paternal ancestors to work with. When you attach DNA to a profile, it usually takes a short amount of time to accumulate SAHs. As it happened, the Shared Ancestor Hints pointed in the direction of K’s Mum’s side of the family.

K had given me further information regarding her Mum C’s extended family, which we then added in to the tree. Then it was time to start attaching Mum’s DNA to other parts of the tree, to see if we’d get any new Shared Ancestor Hints, which helps to ascertain what parts of the tree to focus on and which ones to ignore. At this stage, I am sitting on 12 Shared Ancestor Hints with Mum’s DNA being attached to a new profile in the tree that Rose created, one that would reflect where she could potentially fit in the tree…by doing this, it’s giving me accurate relationship information to those matches that she has shared ancestors with.

Another thing to note is that Ancestry shows you the DNA matches that you share with another person. For example, K and C share 19 DNA matches with Mum. Granted that if these people all have trees, you can work out where exactly they all fit in with you, and lovely Rose worked out a number of their connections to Mum, thus proving that we have one half of Mum’s paternal line proven!

Phew, long post! If you’ve lasted this long, I commend you. I hope it’s made some sense!! To sum up:

  • Mirror trees are an exact replica of a close DNA match’s tree, built out on both sides of the match’s family.
  • By attaching your own DNA to the bottom of the mirror tree, you can look for Shared Ancestor Hints, which can point you in the direction of finding unknown close family.
  • By checking the focus DNA match’s “Shared Matches” section, you may find further connections to assist you in the search.
  • You can attach your DNA to different sections of the mirror tree-no Shared Ancestor Hints? No connection to that particular line.

I hope I haven’t missed anything–any questions? Feel free to ask in the comments!

These are some of the articles/blogs I have read over the past few months that I found useful:

Born In New Orleans: What is a Mirror Tree?

Resurrecting Roots: I Have Created A Mirror Tree: Now What?

Knol Aust: Mirroring A Tree on Ancestry (For Adoptees)



3 Comments Add yours

  1. Luanne @ TFK says:

    Yes, this sounds complicated. As a starting point, I suppose I should attach my DNA to my tree? How do I do that?


    1. On your DNA homepage, there’s a “Settings” button in the top right hand corner-click that, and scroll down the page until you get to “Family Tree Linking” – this will allow you to search for yourself in your tree and attach your DNA accordingly 🙂

      Liked by 1 person

      1. Luanne @ TFK says:

        Yeah, I see mine is linked. Thank you!


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