How Ancestry ThruLines Work

What Ancestry ThruLines are

ThruLines is a feature in AncestryDNA that tries to connect your DNA matches to ancestors in your family tree. It looks at the people you match, compares their trees with yours, and draws a possible path from each ancestor down to you and to those matches.

The key idea is that the DNA is measured, but the family connections drawn around it come from family trees. Those trees are written by other Ancestry members and may contain mistakes. ThruLines is best understood as a hypothesis generator rather than a source of proof. If you want a closer look at checking its suggestions, see our guide on whether ThruLines are accurate and how to verify them.

What you need before ThruLines will work

Based on Ancestry’s own help material and the guides written by experienced genetic genealogists, these are the usual requirements:

• An AncestryDNA test with results that are ready to view.
• Your DNA results linked to yourself in a family tree. If you have not done this yet, follow our steps to link your DNA results to your Ancestry tree.
• A tree that other members can find. Public trees and private trees marked as searchable are generally the ones used. Our guide to sharing family trees on Ancestry explains the privacy options.
• A tree that goes back a few generations. Three to four generations is the commonly recommended minimum, and more is better.
• Access to the feature through your Ancestry membership. Ancestry has changed which features are free and which require a subscription over time, so check your account if ThruLines appears locked.

Your matches also need to have linked trees for the tool to use their information. A match with no tree usually cannot contribute a ThruLines connection, although Ancestry may still use other public trees to fill gaps.

How to find ThruLines

Sign in to Ancestry, open the DNA menu, and look for ThruLines. Menu names and layouts change from time to time, so if you cannot see it, look for it under your DNA results or search the Ancestry help pages.

ThruLines are usually organized by ancestor. You will see a list of ancestors, often with the number of DNA matches who may descend from each. Selecting an ancestor opens a chart showing you, the ancestor, and the matches who appear to descend from that person.

Reading the chart: solid and dotted boxes

Two kinds of boxes appear in the chart, and the difference matters:

• Solid boxes are people who are already in your own tree.
• Dotted boxes are suggested ancestors, often called potential ancestors. They come from information in other members’ trees, not from your own research.

Beneath an ancestor you will often see matches grouped by which child of that ancestor they descend from. Expanding a branch lets you see the matches in that line, the estimated relationship, and the amount of DNA shared, which Ancestry reports in centimorgans (cM).

How ThruLines build a suggestion

In simplified terms, ThruLines does three things:

1. It starts from your tree and your DNA match list.
2. It compares your matches’ trees with yours to look for common ancestors.
3. Where a tree has a gap, it may use information from other public or searchable trees to propose a missing link.

Your match’s tree can therefore connect to you even though your match never listed the ancestor themselves. That is both the strength of the tool and its biggest weakness, because each suggested link is only as good as the trees behind it.

What ThruLines can and cannot tell you

ThruLines can help you:

• See which of your lines have DNA matches and which do not yet.
• Spot cousins you might contact to compare research.
• Find candidates for an ancestor you are stuck on, which you can then research.
• Notice when a match you assumed was on one side of the family seems to connect elsewhere.

ThruLines cannot:

• Prove that a dotted-box ancestor is really your ancestor.
• Tell you which parent a very small match came from with certainty.
• Correct errors that are repeated across many online trees.

The more DNA a match shares, the more reliable the relationship estimate tends to be. Very small matches can occur by chance and deserve extra caution.

Practical tips for better ThruLines

• Build out your tree sideways. Add siblings and their descendants, not just direct ancestors, since these can be the missing links between you and a match. Our guide to adding a person to your Ancestry tree covers the steps.
• Add dates and places. Fuller profiles make it easier for the system, and for you, to tell people with similar names apart.
• Keep the tree searchable. If you set it to fully private and unsearchable, it may not take part in the feature the same way.
• Document what you add. Attach records and notes so you can tell later which facts were proven and which were guesses.
• Check multiple matches. A suggested line supported by several matches descending through different children of the ancestor is generally more convincing than one supported by a single branch.

Common problems

• No ThruLines show up. Check that your DNA is linked to a person in your tree, that the tree is searchable, and that it extends back far enough. If you use a second account, see how to link AncestryDNA results to another account.
• Mostly dotted boxes. This usually means your own tree is thin in that area and the suggestions come from other people’s trees. Treat them as research leads.
• A suggested ancestor looks wrong. It may well be. Compare against original records such as civil registrations, census returns, church records, wills and land records before adding anyone to your tree. The genealogy research checklist helps you check each type.
• Matches seem placed on the wrong side. The grouping can be wrong, particularly for small matches. Use other tools such as shared matches to cross-check.

Using ThruLines responsibly

A reasonable workflow is to use ThruLines as a to-do list rather than an answer key. Note a suggested ancestor, look for documents that support the parent-child links, and only then add that person to your tree as a confirmed relative. Keep unverified people clearly marked, or leave them out of your main tree, so they do not spread into other people’s research.

If you have tested at other companies or want more matches, you may also be wondering whether you can move your AncestryDNA results to 23andMe. The short answer is covered in that article, along with alternatives.