Mike's Rule #14 - The Transitive Law of Genetic Genealogy
Get settled. In today’s class we’re going to talk about the Transitive Law of Genetic Genealogy.
Imagine you have a DNA match to person A, let’s call him Andy. You also match person B, let’s call him Bob. When you look at your Shared Matches for Andy, you see Bob on the list of people with DNA in common. If A=B and B=C (you’re C), therefore A=C. There is a very high probability that you, Andy and Bob all share a common ancestor. If Andy and Bob have good family trees, somewhere back in time you will find a common great-grandparent. Their common great-grandparent is probably your ancestor also.
Most of the time when we process these connections it’s an obvious relationship that we already know about. Sometimes though, you stop and say, “Wait a minute, I know all my great-grandparents and that’s not one of them.” Surprise. You’re going to need a bigger tree.
Class dismissed.
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