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Genetic Distance

The Genetic Distance is a measure of the variance between two Haplotypes (or more simply, a set of STR test result values from two testers). In simplest form, it is the sum of the absolute value difference between each STR value tested in both testers. But some allowance is given for special multi-value STRs. And a few STRs may be ignored or discounted further if from a highly varying group. This calculated value, like the Generation Difference, is a simplification and should only be used as a rough guide. It is used by FamilyTreeDNA to determine if a tester appears in another testers match list.

Generally, depending on how many STRs are being compared, the genetic distance should be fairly small if two testers are on the same patrilineal line in the genealogical time frame.

It is always important to stress that STR values can change back as easily as they change from a given value. That is, a 37 could go to a 36 and then in a few more generations go back to a 37 count. So getting generational estimates to a common ancestor from the genetic distance is more of an estimate than a norm.

As with many terms, the biological meaning is more expressive than the adopted meaning used by the genetic genealogy industry. Biological definitions include measure the numerical genetic distance of whole genomes, not just STR measured results. There is also an application of genetic distance used by some in the genetic genealogy field that applies to mitochondrial DNA but is not covered here or by our project.

External References