An Approach to Genetic Genealogy (Part 2)
Genetic Genealogy is a relatively new hobby & citizen science. There are few rules governing how to run your projects and interact with people with whom you share a DNA test match. Like all new endeavours, everyone is learning. Best practices are developing and being adopted. Some excellent guidance can be found on the many genetic genealogist blogs who discuss better ways of working and how to interpret results. There is also an online community that is busy educating and explaining to the wider group of testers, who may not have a science background or get easily put off by terminology.
The Seven C’s
The following list of Seven C’s is a check list that I have developed over the last two years. It is based on my own personal experiences of untangling my own DNA and working with others. The first C, “Collaboration” is discussed in the previous post, which covers the many issues about getting started with investigations once results are known. The other C’s to be discussed is this post are Confirmation, Conversation, Confidentiality, Context, Consideration & Conclusion.
Verification of every match is very important. Just having a match, especially through a small segment of DNA, may not be genuine.
As a rule of thumb there is an 80% chance of a match being genuine if 7cM (the length of DNA segment in centiMorgans) with number of SNPs at 700 (the number of matching mutations on that segment of DNA). By 5cM it is 50:50 or less, as there is an increasing likelihood of matching through chance rather than common ancestry. You can only be 100% certain of a genuine match with a segment larger than 15cM.
Verification of Ancestry matches is particularly important as their latest algorithm provides matches down to 6cM, well into the zone of high risk for matching by chance. Where data has been shared, I find many don’t stand up to verification by third party tools.
Since Ancestry does not provide the details of matches (through a chromosome browser), also for multiple segment matches, it is impossible to know what may be relevant. A small segment match may be relevant where you have identified larger segments with closer genetic cousins who also share the implied common ancestry, i.e. triangulation. One an purely one-to-one basis, it is unwise to draw too many definitive conclusions, even if a paper trail implies a possible shared ancestor.
Collaboration requires the sharing of Ancestry DNA data to GEDmatch to start the verification process (also available through free copying to Family Tree DNA & MyHeritage).
Once matches are verified, the facts can be discussed. As a genetic genealogist with multiple projects, this often involves sharing additional information (where permissions have been granted) that indicates the vector and common ancestors. It is important that discussions at this stage are purely factual and do not involve any pre-judgment.
All conversations must be confidential, on a one-to-one basis unless wider collaboration is agreed.
Initial conversations must be non-judgmental and factual as the context of a DNA match, especially a genetically-close one, may not be immediately apparent. Even though you are collaborating, the other party may not have fully disclosed the reasons for their research. The traditional and romantic family tree does not apply in genetic genealogy and not all children are conceived in loving or consensual relationships.
There are two types of modern family tree – the paper trail and the one proven by DNA. They frequently do not match.
Confidentiality and Context mean that particular consideration of the other collaborators and their immediate families are required.
With luck, your collaboration will be a rewarding one which will result in a match that is fully understood. Often, you will generate leads or an agreed way forward.
The “Seven C’s” are a result of interaction with many hundreds of people who have tested where many thousands of matches have been evaluated. I also managed dozens of DNA results on GEDmatch on behalf of genetic cousins who are open to collaboration by sharing their data, but do not want to be involved in the detailed matching process.
Mark Grace, Resident Genealogist, Ballynoe House
Facebook research blogs:
The Family of Jeremiah Grace – DNA Project