ANOTHER DNA PUZZLE
September 22, 2024
It's time for another DNA puzzle / tutorial. One of my recent cases had some relationships that I thought would make a good brain teaser for anyone wanting to learn about DNA and centimorgans. Some valuable things can be learned from this one. This puzzle involves four people: William, Justin, Fred, and Chris. I'll show you DNA match lists for all four people. They all match to each other on the paternal sides of their families. Your goal is to determine how they are related with as little information as possible. In a real search, sometimes you have very little information. Maybe no one has family trees made or no one will reply to your messages. How much can you learn from just those centimorgan numbers?
I'll start by telling you, I know exactly how everyone is related, it's all been 100% confirmed. You should know, there's no odd relationships here. There's nothing unusual, like double cousins. There's no incest, or inter-family relationships, and no one is getting DNA from multiple lines of their family tree. The relationships are all very common. You'll need some knowledge of centimorgans to solve this. See my previous posts if you need help.
The main person I was helping was William. He knew who his mother was, but not his father. Take a look at the four lists below. Can you determine relationships by centimorgan numbers alone? You don't need trees or knowledge of any other family members to come up with relationships that would work. Maybe there's multiple possibilities, or maybe not. Examine ALL four lists closely. Maybe you should make some trees to help you. What would make the most sense? How is everyone related to William, and how is everyone related to everyone else?
William's Match List
Chris' Match List
Fred's Match List
Justin's Match List
If you've read my previous posts about centimorgans, then you probably came up with an answer that would make all the numbers make sense. Are you sure you came up with the right answer though? Write down all the relationships you came up with before going any further. Include these six relationships: William's relationship to Justin, William's relationship to Fred, William's relationship to Chris, Justin's relationship to Chris, Justin's relationship to Fred, and Chris' relationship to Fred. If you're already confused, here's an important clue...
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CLUE 1
The Ancestry website does something really foolish. Notice that they put a description of the relationship next to each match. You'll see things like "1st - 2nd Cousin," or "2nd - 3rd Cousin." Always ignore those descriptions. They cause nothing but confusion for many people and they are usually wrong.
Now, I'm going to make things a little tricky. I'll reveal the birth years of the four people. Sometimes knowing people's ages can persuade you to think differently. Note: All of these ages and numbers are based on a real family. None of this is made up. Click the clue to see the ages.
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CLUE 2
William is the oldest. He was born in 1958. Chris and Fred were both born in 1979. Justin is the youngest. He was born in 1996.
If you came up with the relationships I think you did, you're probably scratching your head right now. Now that you know how old everyone is, are you rethinking the relationships? You should at least be checking the relationships to see if there's different possibilities that would make more sense. Click for another clue.
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CLUE 3
The closest common ancestor to all four people is one single man. His name is George. No one is related to the same wife or partner of George.
Based on age alone, it's quite possible we're dealing with DNA matches from three different generations here, right? My next clue will reveal the ages of everyone else involved in this puzzle. I have a previous blog post called, "What Generation am I in?" If you're confused at this point, now might be a good time to read that article.
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CLUE 4
As mentioned in my previous clue, no one is related to the same wife of George. So, George had children with four different women. George was born in 1933. William is a descendant George and Betty. Betty was born in 1938. Chris is a descendant of George and Carol. Carol was born in 1956. Fred is a descendant of George and Rhonda. Rhonda was born in 1934. Justin is a descendant of George and Maria. Maria was born in 1953.
Now you have all the pieces of the puzzle. You know everyone's age. You know how many centimorgans each match has in common with each other. You know who all these people are descendants of. It's time for the answer. Will it be the same answer you came up with at the beginning? Did you change your answer after viewing the clues?
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ANSWER
In this case, knowing people's ages didn't help one bit. It just caused a lot of confusion I'm sure. You could have solved this without knowing anyone's age. Did you come up with this correct arrangement...?
William/Justin: Half-Brothers William/Chris: Half-Uncle/Nephew William/Fred: Half-Uncle/Nephew Justin/Chris: Half-Uncle/Nephew Justin/Fred: Half-Uncle/Nephew Chris/Fred: Half 1st Cousins
What makes this confusing (but interesting) is the fact that Justin is 17 years younger than Chris and Fred, but he is a generation older than them. He is their half-uncle. Justin is also 38 years younger than William, and they are half-brothers. This happened because George married a much younger woman, and she had a child (Justin) very late in life. George is the father of William and Justin, and the grandfather of Chris and Fred. As mentioned in my article about generations, age doesn't determine what generation you are in.
I also want to point out why you could come up with the correct answer even before knowing anything about George or people's ages. Let's say you knew nothing and looked only at Williams matches. You might say, Justin could be Williams uncle and Chris and Fred could be William's first cousins. The numbers work, right? Well, they won't work when you look at other people's lists. Try it. We've made William, Fred and Chris all first cousins. Chris and Fred match each other at only 339cM though. They cannot be 1st cousins to each other. Try other arrangements. Try Justin as William's nephew, or William's grandson. You'll end up with problems there as well.
I hope this puzzle made you think about centimorgans and relationships. Things are sometimes exactly as they appear, and other times, those numbers can really confuse you. I also want to point out a great new feature on Ancestry called Pro Tools. It allows you to see how many centimorgans your matches have in common with each other. Even without contacting those matches, you can see all the centimorgan values, just like viewing the lists above. 23 and Me also has this feature. Knowing how your matches are related to other people can sometimes be just as important as knowing how they are related to yourself.
Next, find out what happens when people refuse to believe the DNA results.