Using DNA as a Tool for Family Research

Mayo Genealogy Group

6 p.m. Friday 12 May 2023

Park Hotel, Kiltimagh

by Paddy Waldron

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General principles

For every autosomal DNA match, and for every autosomal DNA segment, one would like to assign both to an ancestor. Specifically:

Some genetic genealogists have simple family trees and find it more intuitive to assign matches and segments to ancestral couples (the most recent common ancestral couple shared with the match) rather than individuals, but:

For example:

My own family tree has numerous recent complications which force me to think in terms of individuals rather than couples:

Matches who are not known relatives can be tentatively assigned to ancestors (or predicted) based on

Ahnentafel numbering


I recommend using:

So I use different methodologies:


Matches who end up with multiple dots (e.g. four GGgrandparents):
There is an exception to every rule: not only shared but even triangulated matches can sometimes arise by coincidence.

Consider these three marriages in the United Church of England and Ireland (the established church) in Kilkeedy, County Limerick: However, these close triangular marriage patterns are very rare.

You may still find two distant relatives, related to you through different ancestors, appearing as shared matches, because they are related to each other through an ancestral couple whom they share with each other, but whom neither shares with you.

An example: how am I related to Seamus (James) Bermingham:

Conclusion: Why you should submit your DNA

Further reading