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Concepts – Mirror Trees

Roberta Estes

What are mirror trees, and why would I ever want to use one?

Great question.

You’ll hear genealogists, especially adoptees or persons trying to find a missing parent mention using mirror trees.

Mirror trees are a technique that genealogists use to help identify a missing common ancestor by recreating the tree of a match and strategically attaching your DNA to their tree to see who you match that descends from which line in their tree.

I have used mirror trees to attempt to determine the common line of a close cousin whose common ancestor (with me) I simply CANNOT discover. Notice the words “attempt to.”  Mirror trees are not a sure-fire answer, and they can sometimes lead you astray.

Foundation Concept

The foundation concept of a mirror tree is very straightforward.

Let’s say you match Susie as a second cousin. This means that you should share a great-grandparent with Susie. A relationship this close OUGHT to be relatively simple to figure out – except sometimes it isn’t.

Note that vendor relationship estimates are just that, estimates of relatedness based on total and longest cM, and they can be off in either direction.

In the case of third cousins or closer, vendor estimates are generally pretty accurate.

You can view the ranges of cMs and relationships in this chart.

Of course, when you match someone, you don’t know who the common ancestor is, nor do you necessarily have access to their pedigree chart or tree. If you do, and you can easily see the identity of the common ancestral couple, that’s great – but life isn’t always that simple.

In Practice

In my case, I match Susie, and no place in our trees, at ALL, is a common ancestor, let alone three generations back in time. Furthermore, her entire line and my father’s line were all from Appalachia, so common geography doesn’t help.

We matched at Ancestry, so we both uploaded to GedMatch, where we match almost exactly the same, and the relationship prediction is the same as well. Someplace, in one of our trees, is an NPE, a misattributed parentage – because both of our trees are complete back beyond those generations.

Uh oh.

So, I created a tree in my Ancestry account, duplicating Susie’s tree, and making it private – at least one generation beyond great-grandparents – just in case the estimate is wrong. Then, I connected my DNA to her tree, as her.

In my case, I have two DNA tests at Ancestry, my V1 results and my V2 results. I never really thought about this as a way to keep one set of results working for me, connected to my own tree, and to have a second set of results to connect to mirror trees – but that’s exactly what I’ve done. I utilize the second set of results as my “working on a problem” results while the first set of results just stays connected to my own tree.

After connecting my DNA results to the mirror tree and giving Ancestry a couple of days to cycle through, creating connections and green leaf “shared ancestor” hints, I checked to see who my DNA attached to her tree says I match, and which line in her tree “lights up” with match hints. If I can’t tell by connecting my DNA as her, I can also connect my DNA to her parents and grandparents, one at a time – again – looking for green leaf shared ancestor hints in those lines. No hints = wrong line.

This process shows me in which of her lines our common lineage is found – even if I can’t exactly pinpoint the common ancestors just yet.

Instructions

I had planned to provide step by step directions for how to create a mirror tree and then how to utilize the results, but then I discovered that someone else has done an absolutely wonderful job of writing mirror tree instructions. There is absolutely no reason to recreate the wheel, so I’m linking to two articles from the blog, Resurrecting Roots, as follows:

After building a mirror tree, their next article explains what to do next.

Now, if I could just figure out that common ancestor with my second cousin match. You may encounter the same type of challenge.

If the right people haven’t tested yet, you may not be able to achieve your goal on the first try. Or, in my case, it appears that we may have more than one common ancestor – complicating matters a bit. If this happens to you, wait a few weeks/months and connect the tree again, or build it out another generation to increase your changes of a green leaf hint.

The great thing about genetic genealogy is that more people are testing every single day. Give mirror trees a try if you’re an adoptee, trying to find an unidentified family member in a relatively close generation, or are being driven absolutely batty with a relatively close match that you can’t solve!

If you need help solving these types of problems, I suggest contacting dnaadoption and taking one of their classes.  They aren’t just for adoptees.

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Disclosure

I receive a small contribution when you click on some of the links to vendors in my articles. This does NOT increase the price you pay but helps me to keep the lights on and this informational blog free for everyone. Please click on the links in the articles or to the vendors below if you are purchasing products or DNA testing.

Thank you so much.

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