Irish Roots

September 14th

John Grenham


To recap: there are two main types of genealogical DNA test in current use, the Y-chromosome test that can provide evidence of common paternal descent as recently as a few centuries ago, and the mitochondrial DNA test, which can be used to identify common maternal descent over millennia.

Both tests make their identifications by comparing the individual sample you supply with a large collection of samples already known, and then statistically analysing how what parts of the collection your sample is closest to. The more samples in the existing collection and the more points of comparison used, the stronger the statistical evidence. But it is still just statistical evidence, not absolute truth.

So, if the periods they deal with are beyond the coverage of existing records, and the information they provide is only statistical, what use are these tests for genealogy?

The blunt answer is “Not a lot”. The only direct use is a Y-DNA test applied to a single, relatively unusual surname – the best known example is Bryan Sykes’ demonstration that his own surname almost certainly originated from a single individual living around the twelfth century. For individuals with the same name but without any known family connection, such tests can be very illuminating. The best guide to finding, or setting up, such a surname project is in Chris Pomery’s Family History in the Genes (London, 2007).

Beyond genealogy, though still connected, Y-DNA testing has also been used by researchers from TCD’s School of Genetics to examine whether or not some common Irish surnames stem from a single individual or have multiple origins. There is strong evidence that O’Sullivan derives from single man living, most probably around 800 AD, with the original Ryan more likely to have lived around 1400 AD. Murphy and Kelly, on the other hand, appear to have multiple, separate origins.


Comments and suggestions are welcome, to irishrootsatirishtimes.com.

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