25 March 2008

Triangulation in Genetic Genealogy


Below is a paper I wrote and shared with my DNA project members. If you share it, please allow me to receive credit for its compilation. The lineage chart will not come out well on this forum so you are most welcome to email me privately to get a better copy.

Triangulation in Genetic Genealogy

Triangulation is a method of determining the DNA signature (haplotype) of an ancestor using the DNA results of direct line descendants.

If two DNA tests of the descendants of two sons of a common ancestor match, you know the haplotype of the common ancestor.

If there is a mutation (not a perfect match), then one must test the branches of other sons of the common ancestor to determine which branch has the haplotype for that common ancestor and where the mutations occurred in the branches which differ from that common ancestor’s haplotype. The idea is to have two or more lines of descent for each branch that differs from the other branches of the common ancestor.

There are many ways Triangulation can help genealogists:
* It can help determine the common ancestor’s haplotype and thus pointing you in the correct direction for research.
* By testing various descendants of an ancestor you can determine which descendants belong to which son of an ancestor, thus proving a paper trail.
* You can learn the specific haplotype of an ancestor.
* Triangulation can be applied to both Ydna and mtDNA.

If the Y-DNA of direct paternal descendants of two brothers is exactly the same, we know the Y-DNA of the father of those brothers. The father is at the intersection of the two lines from the descendants back through the brothers.

However, the DNA of that ancestor would not be clear if we just looked at one male descendant’s DNA and that of his other son whose descendants have one or two mutations difference from the first tester.

By adding more markers and mutations to the Group mean, then you can hope to determine sub-groups and more recent MRCA for that sub-group.

THIS IS WHY more member samples are so important to any study. More samples confirm the convergence of member genetic profiles and their genealogy at many levels.

DNA Project Example

In this actual example, Bill (Kit 30610) has a perfect 67 marker match with:
Arlin (Kit 30586) and Joel (Kit 36047). All have paper trails from John who died 1740 in Amelia County, Virginia. Bill, however, descends from John’s son Lodwick while Arlin and Joel descend from different sons of Abraham. The chart below clarifies this.

John, d. 1740 Amelia Co, VA
.....had son
........Lodwick, b. 1715
............Descendant Bill (Kit 30610) tested for this branch

John, d. 1740 Amelia Co, VA
.....had son Abraham, b. 1721 and two branches on this line were tested.

.....Abraham son of John, d. 1740 Amelia Co, VA
........had son Frederick, b. c1745
............Descendant Joel (Kit 36047) tested for this line.

.....Abraham, son of John, d. 1740 Amelia Co, VA
........had son John, b. c1760
............Descendant Charles (Kit 30586) tested for this branch.

Typical Triangulation Problem

* Curtis (Kit 30595) has a 67 marker match with the descendants of John of Amelia.
* Curtis has no paper trail to John.
* Curtis’ oldest ancestor is Peyton , b. ca 1790 VA; d. ca 1859; m. Nancy Pitts 25 Mar 1830 in Upson Co, Georgia.

Possible Options

* Test other sons of John to determine if all have the same haplotype as Lodwick and Abraham
* Those who do not have the same haplotype will not be the direct ancestors of Curtis since he matches Lodwick and Abraham perfectly. However, a mutation could occur in another descendant of Curtis. If that is found to be the case, then triangulating that line is important as well.
* If all testers of all the sons are perfect matches, then you must focus on the paper trail to determine Curtis’ path to John through any of the sons.

Non-Perfect Matches

* Genetic Difference of 1 on a 67 marker
.....o Warren (Kit 30609) DYS 413a
.....o Floyd (Kit30726) DYS 393
.....o Joseph (Kit 32477) DYS 449

* Oldest Known Ancestors:
.....o Warren – James M., b. ca 1808 VA
.....o Floyd – James Franklin, b. ca 1884 IL
.....o Joseph – William, b. ca 1812 NC

Genetic Options:

* Triangulation can help determine the common ancestor’s haplotype and thus pointing you in the correct direction for further research.
* Triangulate each tester’s branch separately to determine where the mutation may have occurred.

Test remaining sons of John of Amelia to see if any have the above mutations

* IF one of the sons of John has the mutation that has been received by Warren, Floyd or Joseph, then that is the line to which they connect. This would make them a perfect match to that son.
* IF the other sons do not have any mutations that Warren, Floyd and Joseph exhibit, then test other sons of their respective oldest ancestors or more recent males to see if the mutation occurred in more recent generations.


* You need to test other sons of more recent generations to find where the mutation occurred.
* It is possible that a more current generation received the mutation that appears in the haplotypes of Warren, Floyd and Joseph.
* When you add more markers and mutations to the Group Mean, then you can hope to determine sub-groups and the more recent common ancestor for that sub-group.

Determining a more recent Common Ancestor can help you…

* Find other genealogists and cousins who specially match and can help with the research.
* Provide a focus in targeting specific families with whom you connect more closely, thus narrowing the “hunt.”
* May lead you to the particular descendant who received the mutation, possibly proving your lineage.

©Aulicino, March 2008 Email: Aulicino@hevanet.com

John Carpenter’s email on ISOGG
Charles Kerchner: http://www.kerchner.com/deducedancestralhaplotype.htm