Based on the number of questions I’m receive about triangulation, it’s time to write an article.
There are two kinds of triangulation that we use in genetic genealogy. One type is for the Y chromosome and it’s to determine the original values of the DNA of the common ancestor. The second type of triangulation is for autosomal DNA and it’s to determine if you share a common ancestor with someone and what the DNA of that ancestor looked like.
This article is about the first type, for Y DNA.
Why would you want to use triangulation?
Sometimes in order to know if a particular line has descended from an ancestor, you need to know what that ancestor’s Y DNA marker values were.
For example, if you have an ancestor born in the 1600s, and he had two sons whose descendants tested today, each line could have 4 mutations each, or 6, which could put the matching software over the threshold – meaning they might not be reported as matches. We have this situation in one of the Estes lines that seems to be particularly prone to mutate.
Family Tree DNA has set up match thresholds. For someone to be listed as your match, they need to have no more than the following total number of mutations difference from your results.
|Markers in Panel Tested||Maximum Number of Mutations Allowed|
0 unless in a common project, then 1
So you can see that if you have a high number of mutations in the first panel or two, you might not show as a match.
But if you know what the original ancestors Y-line DNA looks like, then it’s easy to tell that they really are matches and that both lines have simply had several mutations.
It’s much more accurate to compare everyone to the original ancestor instead of trying to compare them to each other.
Let’s take a look at the Estes project by way of example.
Abraham Estes, the progenitor of the Southern Estes line was born in 1647 in Nonington, Kent, England. He immigrated to Virginia in 1683 and began begetting shortly thereafter. His wife was Barbara, and although the internet is full of family trees that say her last name is Brock, there is not one shred of evidence to support that. In any case, Abraham and Barbara had a total of 8 sons who lived and the sons had about 42 sons, so we have a good number of Estes families throughout the US today, mostly descending from Abraham. There is also a northern line founded by Abraham’s cousin, Richard Estes although they don’t have nearly as many descendants.
This chart shows the results of DNA testing through 7 different Estes lines, 6 of which are Abraham’s sons and one of which is a descendant of the Northern line.
The green row at the top is Abraham’s reconstructed DNA, and now, everyone in the project gets compared to Abraham on my spreadsheet.
It’s easy to see how this is done. For each marker, beginning with 393, we determine what the normal value is for the family. For marker 393, all lines carry a value of 13. One line, John through Elisha, shows a mutation to a value of 14 which would signal a line marker mutation for this particular line. This is quite useful, because when we see someone who carries a value of 14 at this location, especially in conjunction with any other line marker mutations that might exist in that line, like a value of 11 at marker 391, we know where to look genealogically to find the tester’s place in the family. Line marker mutations are great guideposts.
So, marker by marker, I’ve reconstructed Abraham, shown at the top in green.
You might wonder why the value of 25 at 390 is red and underscored and 12 at 391 is bolded, red and underscored.
One of the things I do for each of my family lines, and for clients who order Personalized DNA Reports, is to determine which of their markers carry rare values. In this case, the value of 25 at 390 is found in only 16% of haplogroup R1b1a2. The value of 12 at 391 is found in only 4% of the haplogroup R1b1a2 population. My threshold for rare markers is less than 25% and for very rare, 6% or less. Bold red indicates very rare, red indicates rare and the underscore is present so that people printing in black and white can see the difference
Why and how does this make a difference? In a situation where you’re trying to decide if someone really does match the Estes line, this information can be a big help.
The last kit on the chart does carry the Estes surname, but does not match the Estes line genetically. This is obvious by looking at all the yellow squares, which are mismatches to Abraham, but let’s say that this person tested at 12 markers and he matched the Estes DNA on all of our rare markers, but mismatches a couple on the more common markers. This is more likely a true Estes match than if they mismatch us on all of our rare markers. The Estes rare markers combined create a type of family genetic fingerprint. This is particularly important for adoptees.
And yes, to answer the next question, a Marker Frequency Table can be purchased separately for those who want their marker frequencies through 111 markers, but don’t want a Personalized DNA Report, by purchasing a Quick Consult. A marker frequency table looks like this but extended, of course, through all of your markers:
Now, we know what the original Abraham Estes’s DNA looked like. We also know which of our markers are unique. This can also help us when comparing to other surnames we may be related to before the advent of surnames. There is family history to be gleaned from those matches as well.
And lastly, because we also have cousin Richard’s DNA signature, we can use that information to reconstruct the common ancestor of Abraham Estes and Richard Estes, which is the grandfather of both men, Robert Estes, born 1555 in Ringwould, Kent, England. Not bad for genetic technology, reaching back more than 450 years in time and telling us what our ancestor’s DNA looked like, and all without even reaching for a shovel.
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