Creating Your Genetic Family Tree

You’ve probably heard this before – or maybe you haven’t – everyone has two family trees. A genealogical (traditional) tree & a genetic (DNA) tree. If you’ve DNA tested, you’ll want to identify both.

There are plenty of websites that help you to create a genealogical (traditional) family tree. Ancestry, MyHeritage, Family Search among them. Just about anyone can do this because it can start at the most basic level: you, your parents, your grandparents. You put down what you know. If you want to go beyond that, there are plenty of resources out there.

You can take a genealogical (traditional) family tree back as far as the records will take you. If you’re really lucky, that could be the 1600s, 1500s, or even earlier. But for Irish family history in particular, most of us can only go back to the early 1800s, maybe the 1700s.

Your genetic family tree, on the other hand, that’s the ancestors who actually passed DNA down to you. That won’t be every ancestor in your traditional tree. It’s said that most DNA matches share a common ancestor with you within about 8-10 generations. But because of the randomness of DNA, we inherit from some ancestors more than others, and likewise, some less than others. As a result, in some cases, we won’t inherit any DNA at all from a 5th great-grandparent, for example.

On average, here’s how much DNA we inherit from each generation of our ancestors (keyword: average – again, we can inherit more or less at any generation, with the exception of 50/50 for our parents, which is always true – the rest of it, it’s random):

  • Parents (2) – 50%
  • Grandparents (4) – 25%
  • Great-grandparents (8) – 12.5%
  • 2nd great-grandparents (16) – 6.25%
  • 3rd great-grandparents (32) – 3.13%
  • 4th great-grandparents (64) – 1.56%
  • 5th great-grandparents (128) – 0.78%
  • 6th great-grandparents (256) – 0.39%
  • 7th great-grandparents (512) – 0.20%
  • 8th great-grandparents (1,028) – 0.10%

With each passing generation, the amount of DNA you inherit from an ancestor is diluted. That’s why testing the oldest living relatives in our families can be the most fruitful for DNA & genealogy efforts – they inherited the most DNA from our distant ancestors.

When you work on your genetic tree, there’s also the potential for surprises. A branch of your genetic tree may even deviate from your traditional tree. There are many reasons for this, including: Non-paternal events (NPE), misattributed parentage, and adoptions. Of course, these incorrect lineages can theoretically occur at any generation, so even the most well-documented traditional trees need to be evaluated with a critical eye. Our DNA helps to identify those events & the true parentage.

So after DNA testing, how do we keep track of our genetic family tree? How do we visualize it and map it out?

First, use tools like Gedmatch, or Genome Mate Pro, to identify & map out segments that passed down from certain ancestors or families.

Next you’ll want to visualize your genetic tree. Enter DNA Painter, which now has a “Trees” feature that allows you to build out your genetic family tree.

As you confirm ancestors you must have inherited DNA from, based on your segment analysis & digging into your DNA matches, you can signify on DNA Painter that you inherited DNA from them. Over time, you create a genetic tree, which is presented in a pedigree format, a fan format (my preferred method) or in text format.

So let me show you what I’m talking about. Here is my traditional family tree, to date – this is 20+ years of research – how far I’ve been able to take back different branches of my personal family tree. Note that I’m using a different color to represent each ancestor back to my 3rd-great-grandparents. (These colors help to “paint” matches in chromosome browsers).

And below is my genetic family tree. I’ve confirmed that I personally inherited DNA from these ancestors, while the others have faded away.

This doesn’t mean the chart is comprehensive or finished. Not by any means. A traditional tree, of course, can grow over time, as new ancestors are identified. And the genetic tree can grow too, as new matches & segments are identified that you can assign to an ancestor or branch currently not lit up.

How was I able to confirm all of these ancestors above passed down DNA to me personally? Either:

  • The ancestor personally tested. Obviously, in nearly all cases this is not possible. Some of us get lucky & can have a parent or grandparent test, but most of us are not able to do that.
  • Known cousins tested. If multiple cousins DNA test, you match them, and your common matches with them are what you’d expect – other known cousins consistent with that branch of the family, or shared matches who share the same families, this helps to confirm ancestors in our tree.
  • Descendants of siblings of ancestors match us on DNA. If you think about it, anyone who matches us on DNA & is a legitimate match (not a false positive, which can happen with small matches) is a descendant of a sibling of one of our ancestors. The key is to identify which ancestor, and the following help with that process: (1) multiple descendants of the same sibling match us on the same DNA segment; (2) descendants of multiple siblings of the same ancestor match us on the same DNA segment; (3) multiple confirmed relatives consistent with the same branch of the family match us on the same DNA segment. The same DNA segment part is critical, and it’s why a tool like Gedmatch is important. Sometimes we are related to someone in more than one way, so it’s not always what it appears at face value.

In other words, we identify ancestors in our genetic tree through extensive segment analysis, identifying matches, and building up evidence over time. And that’s what DNA does for us in genealogy: it provides evidence. Just like any other traditional record – census, vital, church, whatever – gives us evidence to expand our family tree, the genetic footprint provides evidence for who we’re actually related to. Because what is in print or in writing isn’t always the true story. That’s not to say everyone is bound to find lots of surprises in their family tree, but you do need to keep an open mind until you verify each branch.

When you compile enough evidence, multiple matches on the same segment, consistent with the same family, and frankly multiple segments for each family, that’s when you achieve proof. And your genetic tree can reflect that.


One comment on “Creating Your Genetic Family Tree”
  1. Pat K says:

    Very nice layout and professional

    Liked by 1 person

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