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This week Dr. Maurice Gleeson, founder of Genetic Genealogy Ireland and expert in practical guidance on how to use DNA to advance your genealogy talks to us about managing all those matches when we first do our DNA! This is a must-read for anyone who has or is thinking of using DNA to further their research. 

DNATesting (1)

When you first open your DNA results, you are faced with thousands of matches. These are people who share some identical segments of DNA that you have. And the reason why they share the same segments with you is because you have both inherited these specific identical segments from the same common ancestor. The question is: who was this ancestor? And figuring that out can lead you to breakthroughs in your genealogical research. Brick Walls will come tumbling down.


And that is where the fun part begins. How do you manage your 10,000+ matches?

Top Tip #1 Arrange Matches into Clusters

The good news is you only need to focus your attention on your top matches initially. And we can do this relatively easily by arranging our matches into clusters of “shared matches” i.e. matches who match each other. The theory is that most people in a cluster will match most everyone else in that cluster, the reason being that many of them share the same common ancestor.

So, for example, we can start at a very basic level and simply divide your matches into two large groups – those that are related to you via your mother’s side of the family, and those that are related to you via your father’s side of the family. We could then further subdivide each of these groups into two further subgroups (giving 4 subgroups altogether), representing people who share DNA with you that was passed down to you via each of your 4 grandparents. And we could keep doing this, going back an extra generation each time. But starting with just 4 groups is a good place to start.

Arranging your matches into different clusters can be done in a number of different ways. You can use a paper and pencil, a spreadsheet, the coloured dots system on Ancestry or MyHeritage, or the auto clustering tools on the Genetic Affairs website. [1]

Once you have identified some clusters, pick one and start to analyse it, preferably one that has some of your known cousins in it, which will allow you to identify the common ancestral couple through which you received the matching segments of DNA. In this way you can focus your attention on a known ancestor (or couple).

Top Tip #2 Analyse Clusters by Adding Matches from your Family Tree

I personally tend to use a spreadsheet for analysing clusters. I start by adding my matches on Ancestry and then my matches on MyHeritage, FamilyTreeDNA, and GEDmatch (if any). I record the amount of DNA shared and the estimated relationship. I then compare family trees (where available) of all the matches in the cluster, searching for a common ancestor, or, failing that, common ancestral surnames or locations. I then record the line of ascent to the common ancestor for each match in the cluster, or, failing that, to their MDKA (Most Distant Known Ancestor) with the common ancestral surname. You can see this in the example below (which uses fictitious names).

DNA Cluster Analysis Example

Figure 1 : Cluster Analysis Spreadsheet showing the list of matches in a cluster, together with their lines of ascent to the common ancestor

Top Tip #3 Look for Bridging Matches 

I also look out for “bridging matches” i.e. matches that have tested at more than one company, which effectively allows me to merge the cluster they belong to at one company with the cluster they belong to at another company. Another way of merging clusters from different companies is to look out for a “bridging ancestor” i.e. the same common ancestor appears in clusters on two or more company websites – such clusters can be merged in my spreadsheet.

In the end, I have all the data from different companies summarized on a single page. And at a glance I can see where everyone fits into the wider family tree for that particular cluster. I can also easily calculate the nature of the relationship between me and my matches in the cluster, and use the Shared cM Tool [2] on the DNA Painter website to double-check that the amount of DNA we share is in keeping with the estimated relationship.

This approach makes it much easier to make contact with these matches and ask them specific questions about the common ancestor in question, in the hope of breaking through a Brick Wall. In this way I have made breakthroughs on several of my ancestral lines.

In one instance, I was able to add an additional five generations to my Morgan ancestral line, thanks to rare documentation that was held in a personal family archive by one of my matches. This took my Morgan line back to Limerick in the early 1600s. [3] In another case, I made contact with a match who shared her grandmother’s recollections recorded in the 1940s. This allowed me to identify a brother of my great-great-grandfather.

It is these types of documentary evidence that you won’t find in public repositories that will often lead to the breakthrough you are looking for. The challenge is to find the right match who has this information, and that means writing to everybody in the cluster … and learning to deal with the frequent response “no, sorry, can’t help”. But I always remind myself: you only need to be lucky once. So perseverance is essential – if you throw enough mud at your Brick Wall, some of it will stick.

Additionally, if you have an ancestor with a common name (e.g. Patrick Kelly), your DNA matches in a cluster may help you focus your research in the records on a particular family or location.

In this way, DNA is a great pointer … it gives you new ideas about where to look.

Maurice Gleeson

Education Ambassador, ISOGG

Honorary Research Fellow, Strathclyde

Founder, Genetic Genealogy Ireland

Sources & Links

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