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The Lost Colony Research Group

Genealogy ~ DNA ~ Archaeology

Newsletter

May  2012

Line Marker Mutations

By Roberta Estes

Line marker mutations can be very useful tools to help determine where in the family tree DNA participants fall. Line marker mutations occur when one particular line of the family experiences a mutation at a particular marker. You can tell that this happened because their value as compared to everyone elses will be increased or decreased. Let's say for example that marker 388 has a value of 12 in your line. But in one line, it's 13. That a great thing and exactly what genealogists want to see, because once you figure out where in the line that mutation occurred, you can use the value of 13 to quickly identify the line of the family that anyone who tests in the future belongs in.  

But how do you achieve this?  

What you have to do is to test at least one person who descended from each generation until you find the generation with the mutation. 

For example, let's say the original ancestor had 3 sons. You've tested a descendant of each of them and you know that one son's line has a mutation but the other two don't. So you know which was the "original" value for the marker because you had 3 sons to test. This is called triangulation.

So for the sons line with the mutation, you know that anyone who shows up WITH this mutation, a 13 in this case, is likely from that sons line. We'll call him John.  

But what you don't know is when that mutation happened. If it happened with John himself, it's your lucky day, because then anyone who shows up with that mutation is IN that line and anyone without it is NOT.

So to determine that, you need to test two of John's descendants through two sons. If they both have the mutation, you're home free. You've already tested one person, which is how you know the mutation occurred, so what you need now is a descendant through a second son.

But let's say they don't have the mutation. Now you know that the mutations didn't happen in John's generation, and only the son to have the mutation is John's son, Robert, your line. Let's say Robert's descendant tested WITH the mutation. So now we know that this mutation is a line marker mutation for John's son Robert's line.  

Let's say your ancestry chart looks like this.  

· Original progenitor (no mutation)

· John (no mutation)

· Robert

· Mike

· Sam

· William (no other males)

· you (had mutation)

From the above, we know that the mutation happened in either Robert, Mike, William or you. By process of elimination, you can figure out which generation the mutation occurred in.  

Let's say that your father, William, is dead and you have no male siblings, so you can't test that directly.

Go on up the tree to find a male, not in your direct line of any one of the other men (Robert, Mike or Sam), but a second son.

Let's say that Mike had another son (not Sam) and you know one the male descendants with the surname. Test this man. Let's say he HAS the mutation. Good. Now we know that William would have had it too, since you do.  

The only question left now is whether the mutation happened in Robert's generation or Mike's generation. You can determine this by testing a descendant of another son of Robert.  

Why is this important? If the mutation just happened in the last generation or two, it's not going to be a lot of benefit to you. You already know your cousins and who they are. But if it happened far up the tree, where you don't know the descendants, it's a powerful tool to be able to find a line marker mutation and to then be able to quickly identify who belongs where in the family tree by using it.  

In the example above, it's a reasonably powerful tool, but not as much so as if John himself had the mutation. The way it works now is that if a participant has it, you know they are in this line someplace between either Robert (whose second son is as yet untested) and your generation. So you know it's in Robert's line. But what you don't know is if it's in all of Robert's line or just his son Mike's line. I have intentionally left Robert's second son untested in this example so you can see some ambiguity. Now of course, it's easy to see that if you find a descendant of a second son of Robert to test, you'll know quickly if the mutation happened in Robert's generation (if his second son has it), or in Mike's generation (if Robert's second son does not have it.)  

So below, is what the final tally of what our DNA testing shows us.  

· Original progenitor (no mutation proven by triangulation)

· John (second son has no mutation so he does not have mutation)

· Robert (second son untested - we don't know if Robert has mutation)

· Mike (second son HAS mutation, so Mike has mutation)

· Sam (by inference we know Sam has the mutation because Mike's second son has the mutation too)

· William (no other males to test - but we know he has the mutation because Mike and Sam do)

· you (have mutation)

If you have a person who tests and does not have the mutation, then, in this example you know he's one of the progenitor's sons, but you won't know which one (unless there is a second line marker mutation, but let's not complicate things). You also don't know, in this example, if he is through John's son Robert, whose line is as yet unproven as to the line marker mutation. What you do know is that the person without the mutation is not in Mike's line, for sure, because we know that Mike HAD the mutation. 

The further up the tree the line marker mutation occurred, the better it is for genealogists.