Genetic triangulation

Genetic triangulation can help determine the most recent common ancestor (MRCA) to a group of individuals

Genetic triangulation is a term derived from surveying that describes a method of determining the Y-STR (short tandem repeat on the Y chromosome) or mitochondrial DNA ancestral haplotype using two or more known data points. The term "Genetic Triangulation" was coined by genetic genealogist Bill Hurst in 2004. Triangulation has been used in various fields, including maps, navigation, and different sciences. In the context of genetics, triangulation is used to determine the common ancestor by comparing the shared DNA segments from known relationships, which by confirming descent from a common ancestor, assigns a specific segment to that ancestor. A triangulated DNA segment has at least three DNA matches that are all connected to each other genetically on the same position. The length of each line in this genetic triangle represents the relationship between individuals, as measured by their DNA testing site in centimorgans.

Genetic triangulation for family research

Triangulation is an essential tool in genealogy, as it helps confirm the paper trails (traditional genealogy) back to the most recent common ancestor (MRCA). When this is repeated several times back to a common ancestor, researchers can recreate the DNA markers or genetic fingerprint of that ancestor without exhuming their remains. Without triangulation, shared DNA matches are found by chance. For triangulation, it is recommended to analyze segments that are at least 7 cM or above on chromosomes 1-22 and 15 cM or above for the X chromosome. Boundaries in triangulation mean that all three or more people are matching on a common segment in order to triangulate. However, it is likely that some people do not match on the entire segment, which then reduces the size of the triangulated segment. Genetic triangulation can help genealogists figure out how they are related to their DNA matches or identify an unknown ancestor on their family tree. By using triangulation, researchers can focus on specific matches that are likely related to the ancestor in question and use genealogical research to confirm the theory that the matches share ancestry on a particular line.

To find a new DNA match to triangulate with at least two individuals, it is necessary to go to a testing website and look for a tool that helps identify matches shared with someone else. Using this tool produces a list of other people who share DNA match with both known individuals. All of these people are new matches, forming their own "triangle with the already known individuals. Because these people are all sharing DNA with the known people, it can be theorized that they are all related somehow to the common ancestor, either as their descendants or as descendants of either ancestor's ancestors. On MyHeritage, the Chromosome Browser and Autoclusters are useful genetic triangulation tools.

Genetic triangulation in Autosomal DNA testing

In autosomal DNA testing, triangulation is the process of reviewing the pedigree charts of people who match on the same identical-by-descent (IBD) autosomal DNA segment to see if a common ancestor can be found. The technique is best used in conjunction with chromosome mapping. Triangulation can be used going back many generations; however, well-documented pedigrees are necessary for all matching parties to rule out the possibility that the match is not on a more distant line that has not yet been researched. Caution still needs to be exercised when reviewing matches with smaller segments under 15 centimorgans (cMs) in size, and especially segments under 10 cMs in size, as many of these are false positive matches, known as identical by state. The role of imputation plays a very important role in triangulation, as this can cause some false negatives for small segments.

See also

• Genetic genealogy

References

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