Getting the best out of an autosomal DNA test

This blog post is based on my experience using AncestryDNA^® for family history research.  AncestryDNA is an autosomal DNA test which (subject to statistical variation) is a “broad spectrum” test covering all antecedent lines.¹ Much of what I say will, however, be applicable to any autosomal DNA test system, but Ancestry does have the biggest sample set of tests.

Once your DNA sample has been analysed Ancestry provides three sets of results:

1. An Ethnicity Estimate,
2. A list of all your DNA Matches with shared DNA equal to 8 cM or greater,
3. ThruLines^TM, a suggested line of connection, based on analysis of Ancestry family trees (private and otherwise) if one can be found.
   

Further background on the AncestryDNA testing and analysis process is available on the Ancestry web site.²

1. Ethnicity

Unless you are primarily interested in anthopology, the Ethnicity Estimate doesn’t help much with family history. Due to the random nature of DNA inheritance, the whole of a particular ancestor’s DNA can have disappeared from your chromosome set. I have 4% European Jewish DNA. A remote cousin via my Jewish ancestors has none.

2. DNA matches

When I first did my test this was the only result useful for family history. Even so the usefulness depended on how much work the matches had put in their end and how accurate that work was (and whether, like me, they prefer to keep their tree private). I have three first cousins in the list whom I know and who were already in my tree. Two of them have online trees, helpful, but mainly containing information I already knew.

The next three with 93-109cM match values have no trees and minimal information on their profiles. By looking at the shared matches I can assign them to either my mother’s or my father’s side and define a rough branch. Two of them have surnames which do not appear in my tree. I don’t know where to start looking for them. The third has a family surname, but I still can’t track him down.

No tree, no personal info, no use (even with high level of DNA match).

The next match (91cM) had a family surname and a VERY small tree, most of which were living people, but she had linked her DNA to it and the one named person was in my tree. I was able to investigate her line and add it to my tree.

Even a small tree is useful as long as it is accurate.

A match at 58cM had a private tree. Even though it is linked, the only way I can directly make use of it is by contacting the owner and requesting access. I don’t blame them. When I first subscribed to Ancestry (15 years ago) I uploaded my careful research to a public tree and found large chunks of it taken and attached to totally unrelated trees. So I made my tree private and have happily shared it with anyone who requests access and can prove how they are related to me. This process can be tedious and this is where ThruLines comes in (see below).

Be prepared to respond to tree access requests in a reasonable and timely fashion if you want to keep your tree private.

A match at 24cM was linked to a public tree with 13,000+ people. Dead cert you might think? There were a lot of common names, but no matching people and no obvious common ancestor(s). The shared matches indicate my mother’s side, but that is as far as I can go.

Accuracy matters more than size in a tree.

3. ThruLines

Added in the last year or so, ThruLines is where Ancestry’s size comes in. Despite all the people who don’t bother with a tree, there are enough trees on Ancestry (with or without DNA links) for someone to have some of your lines in their tree somewhere – as long as what you have in your tree is accurate and you link yourself to it. And this applies to private trees too. You are no longer totally cutting someone off from your tree if you keep it private.

My 91cM match has a relationship suggested in ThruLines, because the linked tree is accurate, even though she only has 8 people in her tree.

My 58cM match with a private tree has a relationship suggested in ThruLines even though her tree is private. I can fill in my relationship with her without accessing information she prefers to keep private.

My 24cM match with a 13,000+ tree does not have a relationship suggested in ThruLines. Considering how many other relationships ThruLines suggests for my tree, I conclude that there is an error in the other tree.

To get the best out of ThruLines you need to link your DNA result to an accurate tree.

My experience with ThruLines is that it is ~75% reliable. It is dependent upon people having accurate trees. For most of the other 25%, you can work out what has gone wrong and still make use of the ThruLines information, but I have had one case where the suggested relationship was rubbish, even to the point of suggesting a relationship on my Father’s side when all the shared matches were on my Mother’s.

With ThruLines, don’t just copy, CHECK carefully.

The final thing I have to say is: what a waste it is to do a DNA test and then do nothing with it. Just a teensy tree with your result linked to it can help. Alternatively, find a relative you trust and let them manage your DNA result and link it to their tree.³

Sources

1. International Society of Genetic Genealogy Wiki, ‘Autosomal DNA’, https://isogg.org/wiki/Autosomal_DNA, accessed 23 Aug 2021.
2. Ancestry Australia, ‘Ancestry DNA White Papers’ https://support.ancestry.com.au/s/article/AncestryDNA-White-Papers3, accessed 23 Aug 2021.
3. Ancestry Australia, ‘Assigning a Manager to Your AncestryDNA® Test’, https://support.ancestry.com.au/s/article/Assigning-a-Manager-to-Your-AncestryDNA-Test, accessed 24 Aug 2021.