Triangulation Method for Deducing the Ancestral Haplotype in Y-DNA Surname Projects

Source: Genetic Genealogy DNA Testing Dictionary, Kerchner, 2004

Triangulation - /tri·an·gu·la·tion/ - A method of determining the Ancestral Haplotype from the haplotype data of known direct line descendants. In Genetic Genealogy, the process of determining the Y chromosome DNA Ancestral Haplotype of a male ancestor by looking at the allele values of the DYS markers in the haplotypes of the tested individuals in a surname project who descend from that ancestor by focusing specifically on the direct paternal line descendants of two or more known and different sons of the common male ancestor. Unless there is an exact match at all alleles at all DYS markers in the haplotypes of the two different direct male lines of descendants, at least three haplotypes are required to triangulate and deduce the ancestral allele for each marker. A typical descendant chart looks like a triangle with the ancestor at the apex. See this page for an example of a Descendant and DNA Inheritance Chart. The analyzer looking from the bottom generation of the chart is looking towards the ancestor from a different descendant locations and thus directions on the descendant chart, i.e., triangulating towards the target, the common ancestor. Thus the term triangulation is used to describe this Genetic Genealogy haplotype analysis technique. This process is analogous to triangulation techniques used in locating hidden radio transmitters by triangulating with directional finders from different directions in attempting to deduce the precise location of the hidden radio transmitter, i.e. the source of the emissions. Likewise by triangulating in Genetic Genealogy we are trying to determine the most precise estimate of the Ancestral Haplotype of the common male ancestor, i.e., the source of the descendant haplotypes. In a Genetic Genealogy example, if at the Y-DNA Genetic Marker DYS 449, two direct line male descendants from two different sons of the ancestor have an allele value of 27, and a third direct line male descendant has an allele value of 28, then logically the allele value of 27 is most probably the ancestral allele value at that marker. If the common ancestor had an allele of 28 at that marker, then two descendant lines would have had to mutate instead of one for the descendant branch haplotypes to be as they are today. Not as probable as one line or branch mutating. The descendant whose allele is 28 at that marker is the one who probably has the mutation in their direct line. To increase the confidence level of the deduction in the triangulation process, add a direct male line descendant from a fourth known son of the ancestor or even more independent direct male descendant lines, if available and if needed. Once the ancestral allele is triangulated and deduced for each DYS marker, all the ancestral alleles for all the alleles are combined together to form the Ancestral Haplotype. See my Kerchner Surname Project 37 Marker Haplotype Table and/or my Laudenslager Surname Project 37 Marker Haplotype Table for examples of determining the deduced Ancestral Haplotype using the triangulation method. Note: The Ancestral Haplotype cannot always be precisely deduced due to insufficient data for a particular surname project, i.e., not having enough independent direct male line descendant branches with surviving males to test. Triangulation can also be used for maternal lines of descent, i.e., determining the mitochondrial DNA Ancestral Haplotype of a female ancestor by triangulating with the haplotype data from direct maternal line descendants of two or more daughters of the common female ancestor. However since maternal line mtDNA SNP based genetic marker haplotypes mutate at a much slower rate than Y-DNA STR based genetic marker haplotypes, one can usually triangulate and deduce the mtDNA Ancestral Haplotype with only two haplotypes from direct maternal line descendants of two or more daughters of the common female ancestor since in most cases the two haplotypes will exactly match with mtDNA analysis in a time frame of genealogical interest. Historical Note: The word triangulation for the name of this process which has been used by various project administrators over the last four years was suggested by William R. Hurst for the simple example of two males from different direct male line descendant branches of a common male ancestor whose test results yielded exactly matching haplotypes. In that case the haplotype shared exactly by the descendants is obviously the Ancestral Haplotype. However if the direct line male descendants do not match exactly and instead have a mutation or two in their respective haplotypes the problem of deducing the Ancestral Haplotype becomes a little more detailed and complicated and the project administrator needs at least three independent direct line male descendants on different branches down from the common male ancestor. But the triangulation approach is still valid. Instead of comparing the whole haplotype as William did in his simple example, the project administrator has to compare each DYS marker one at a time as described above and then compile the Ancestral Haplotype. The definition, analogies, and process was expanded and refined for more complex situations by various online posters, including myself, via a dialog and interchange on the Genealogy-DNA-L mail list at Synergy at Work! For more information on this new Genetic Genealogy term and other terms used in Genetic Genealogy see my Genetic Genealogy DNA Testing Dictionary.

While the Ancestral Haplotype at times can also be the Modal Haplotype, it is not true in all cases. Thus the Triangulation Method must be used to accurately determine the true Ancestral Haplotype, not the mode. See this example

Ancestral vs. Modal Haplotype

Kerchner's Genetic Genealogy DNA Testing Dictionary

What is a Henry Number? How Does it Show Descendants' Relationships to Each Other and a Common Ancestor?

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C.F. Kerchner & Associates, Inc
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Created - 1 Jan 2005
Updated - 6 May 2008