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Triangulation is a term derived from surveying to describe a method of determining the Y-STR or mitochondrial DNA ancestral haplotype using two or more known data points. The term was coined by genetic genealogist Bill Hurst in 2004.[1]

The technique is also used in autosomal DNA testing to compare matching DNA segments to determine which ancestor donated which particular segment. To get started make a spreadsheet with segment data and look for overlapping segments from a common ancestor. If you have at least three people with the common ancestor matching on the same segment then you can infer that the segment came from that ancestor. However, caution needs to be exercised as it is still possible that the match is a false positive (identical by state). This is particularly the case with small segments below 11 cMs. Triangulation is best used in autosomal DNA testing in combination with chromosome mapping. The process of triangulating segments is greatly facilitated by the use of third-party tools such as those available from GedMatch and DNAGEDCOM (eg, Don Worth's Autosomal DNA Segment Analyser).


Further reading

Autosomal DNA



  1. William Hurst. New words for this new field of genetic genealogy. Genealogy-DNA mailing list, 16 December 2004.

See also