ThruLines is a powerful feature of AncestryDNA that automatically shows how you are related to your DNA matches. This is especially useful for those matches that are more remote and don't share recognisable surnames.
ThruLines™ combines the data in your DNA matches with the data in the family trees that you and your DNA matches have provided, filling in people that were missing from each tree if necessary. For example, if your tree goes back three generations and your matches tree only goes back one or two generations, but you share an ancestor four or five generations, ThruLines can show you the relationship. It will even make the link if the matches tree is private.
This feature is extremely powerful, as Ancestry automatically deduces how you are related to a DNA match by scanning through the family trees of you, your DNA matches and even other people who haven't done DNA tests. Provided the names, and birth and death years are a close match it will deduce the relationship and show it as a tree diagram. Sometimes it is not completely accurate if there is an extra or missing generation in someone's tree, and sometimes it won't show a relationship because of mismatching data in the trees, but it can save many hours of manual work. All you have to do is check the tree with traditional records to be sure.
There are two ways to get to the ThruLines screen area - through the main DNA screen or by clicking on a DNA match that is shown to have a common ancestor.
Select DNA on the Ancestry menu, then click on the ThruLines panel on the right-hand side of the screen.
Then choose an ancestor for whom you want to find relatives.
Alternatively...
Select View All DNA matches, then search for matches where Ancestry has identified common ancestors. You can do this quickly by pressing the Common Ancestors filter button.
Click on a match in the list of results, like this one below.
On the left-hand side of the match screen, you will see the shared ancestor(s).
Click on View Relationship to see the ThruLines diagram.
Now, consider this real ThruLines example from my Esdaile ancestors.