How can I use the results of a DNA test to uncover the true identity of my mum’s 4x great grandmother?
‘Mitochondrial DNA cannot refine a search to a country or region’
QI have found a record for a Mary John, baptised in December 1763, parents Morgan John and Mary. I think that she’s one of my mum’s 4x great grandmothers. Possibly the mother was Mary Rees, who married Morgan John in Bristol in April 1763. There’s another Mary John baptised in Gloucestershire around the same time, but which is the right family? Mum and I have done a DNA test (including mtDNA on mum’s). Mum is haplogroup T2b, which is of Welsh origin going back on Mary John’s branch. How can we find the right Mary John? DNA is pointing to her family being from Glamorgan. Emma Candy
AMitochondrial DNA (mtDNA) testing can be very interesting for learning about your deep ancestry on your direct maternal line (your mother, your maternal grandmother and so on), but it is less useful for genealogy and cannot refine a search to a particular country or region. This is because mtDNA mutates very slowly, so there are generally no defining markers that are able to distinguish people within a recent timeframe.
It is best to focus on the exact mtDNA matches – those with a genetic distance of zero – but even then, the match could still date back 1,000 years or more. In addition, it is common to have matches with people from many different countries. To follow up on your deep ancestry, you can join the Haplogroup T2 Project at FamilyTreeDNA. Find out more information at familytreedna. com/groups/t2/about/background.
You should instead focus your attention on your autosomal DNA matches. It was not clear from the question where you had tested. Ideally you and your mum should test at AncestryDNA ( ancestry.co.uk/dna)
because it has the largest database, but it also helps to upload your raw data to familytree dna.com, myheritage.com and livingdna. com to get all of the available matches.
The most effective technique is to assign your matches into clusters by working with your shared matches/in-common-with matches; see my article in the November issue. You can then look at the trees of all the people in each cluster, and see if you can identify a common ancestral couple. Are you in touch with any second or third cousins who descend from Mary John? If so, you could encourage them to test. This will help to identify a cluster of matches to work with. However, you should remember that people from many different counties moved to Bristol and married there, so it is not clear that either of the possible baptisms you have identified is correct. Parish registers from Wales are widely available on the major subscription websites. Debbie Kennett