WATCH OUT!
Be very wary of small matches sharing less than 15 cM. Many of these are false or very ancient matches, and may not reflect the genealogical relationship you’ve identified. have more than 150,000 matches, including over 30,000 that are located in the fourth to sixth cousin or closer range. The process of assigning matches to your tree is much easier if you have done extensive research into all of your ancestral lines going back for about five or six generations. It also helps if you have researched not just your direct ancestors but also all the collateral lines. In genealogy we are mainly focused on taking our trees further back in time, but for DNA it really helps to document the descendants of ancestors right down to the present day because these are the names that will be showing up in your match list. If you recognise the surname you’ll probably be able to work out immediately how you’re related.
Ancestry has some very useful features, such as ThruLines and Common Ancestors (see the box on page 21) which take a lot of the hard work out of the process of identifying common ancestors by showing the potential pathway through which you are related. However, in order for these features to work you need to upload a tree to ancestry. co.uk and link it to your DNA account. The tree must be either public or private and searchable. Names in private and searchable trees appear in search results, but your matches will need to contact you for full access to the tree. Not everyone likes to share their research on Ancestry, so if you prefer you can share a skeleton tree with basic names and dates but no detailed sources.
‘It helps to document the descendants day’ of ancestors down to the present
While many of Ancestry’s DNA features are free, you will need to maintain a subscription to ancestry.co.uk to access additional details and in particular the detailed family tree information. If your match has uploaded a family tree you will be able to see a five-generation preview tree, which provides the names along with the birthdates and death dates, but without any locational information. If you have a subscription you can click through and access the full family tree, which may go back many more generations.
Interpreting Matches
Ancestry provides information about the predicted relationship and the amount of DNA shared measured in centiMorgans (cM). In general, the higher the total cM count the closer the relationship. Another important way of determining relationships is to look at the frequency of a segment of DNA in the population. However, it is important to note that not all of the DNA that
Ancestry’s very useful tools ThruLines and Common Ancestors can help you to identify your connections with your matches.
The Common Ancestor hints first identify that you have a DNA match with a cousin. The algorithms then search through the two trees to see if a common ancestor can be found. You are given the names of the common ancestors. Clicking ‘View relationship’ reveals the pathway via which you may be related.
ThruLines takes this process one step further. It uses sophisticated machine learning to deploy the power of the large collection of family trees at Ancestry, which have been stitched together to form one giant tree. You can click on the common ancestor’s name, and the tool will identify all of the people in we share with other people is shared because of a recent genetic relationship. We can share DNA because we all descend from the same population or the same ethnic group. If a segment is your match list who are believed to descend from this ancestor. The potential descendancy pathways are shown with dotted lines. Click on the green ‘Evaluate’ button to see the records and family tree information that have been used to suggest the connection. ThruLines will also identify potential ancestors, who are similarly shown with dotted lines. You will find that some connections have been worked out by looking at links from multiple family trees. Some people will appear in the trees as private. These are either living people, or people in private searchable trees.
Although these clues are valuable, they will need independent confirmation because ThruLines and Common Ancestors rely on the information contained in others’ family trees. shared, for example, by large numbers of people from Yorkshire or Ireland then it is likely to date back a very long way, whereas if a segment is of genealogical relevance then it is only going to be shared by a few cousins or close relations.
Ancestry has a proprietary algorithm known as Timber which is applied to all matches that share 90 cM or less. Regions of the genome where there is significant overmatching are downweighted, and the revised cM total will give a more reliable estimate of the actual relationship. Ancestry now shows the total cM shared both before and after the application of Timber. However, this feature has not yet been rolled out at the time of writing, so we will need to see how it
In order to find the connections with your matches it’s often necessary to do some tree building, working both upwards to identify the common ancestor and downwards to identify the pathway to your living cousin. Probably over half of the people who have tested with Ancestry are either beginners or have only tested to get the ethnicity estimate, so you will have to do the genealogical work for them.
You can do the research in your family tree program, but it’s often easier to create a private unsearchable tree on Ancestry to serve as a sandbox where you can explore the connections with your matches without having to worry about adding incorrect information. Once you’ve begun to build the tree Ancestry’s hints will start to work, and you can easily review the hints and accept or reject them. You can also quickly copy any information included in other people’s trees.
Experience has shown that it is better to have one big research tree. You can add unconnected people as floating branches. To do this, you will need to add the new person as a child or partner of an existing person. Then edit the relationship of the new person in their profile to disconnect them from the partner or parent.
Use the default MyTreeTags, such as ‘DNA Match’ or ‘Common DNA Ancestor’, to label connections or create your own custom tags.
For a practical example of tree building, check out Blaine Bettinger’s YouTube video on quick-and-dirty trees: bit.ly/yt-blaine-trees. information about the number of segments shared and the length of the longest segment. In general, matches that share more than one segment will be easier to assign and of more recent origin. If you only share a single segment of DNA then the match could potentially trace back 10 generations or more. However, there are sometimes discrepancies with the number of segments. I’ve found examples where one of my parents shares a single segment with a match but the same person shares two segments with me.
Size Matters
Knowing the length of the longest segment is going to be most useful for people from endogamous populations, and can help to determine which of their matches they are actually related to with longer segments being more indicative of recent relationships. For example, a match who shares 98 cM across seven segments with a longest segment of 31 cM is going to be considerably more relevant than a match who shares 98 cM across 11 segments with a longest segment of 16 cM.
You can also look at the average segment size. A 98 cM match with 11 segments has an average segment size of under 9 cM, and these small segments are likely to be the result of background relatedness in the population or connections through multiple distant ancestors rather than a recent family relationship. For endogamous populations it is generally recommended to focus
on matches that share a longest segment of 20–30 cM.
However, don’t expect to be able to identify connections with all of your matches. Every match over 30 cM is generally worth pursuing. Matches in the 15–30 cM range may share a common ancestor, but many matches in this range will be very distant and can’t be identified. As the amount of shared DNA starts to decrease, it becomes more difficult to assign relationships and there is an increasing chance that the matches will be false. If you’ve tested both of your parents then you will find that you have a significant number of small matches that don’t match either your mother or your father.
If you have a match with a name you recognise, the first thing to do is to look at the total cM shared. You want to check that the amount of DNA shared