How Does ThruLines Work?

A Segment-ology TIDBIT

To understand how it works, we need to think like the ThruLines algorithm does. I’m pretty sure the algorithm has three parts: 1) start with two DNA Matches (you and someone else); 2) find a Common Ancestor in their Trees*; 3) find and report the path from the CA down to you and the path down to your Match.

The TL algorithm has no way to check to see if the ancestral lines back to the CA are correct or not (witness the TL reports that report incorrect genealogy). It doesn’t know if the lines are even biologically correct or not – it relies on what you and your Match have entered into your respective Trees. TL also does not check spelling of the names of the descendants from the CA – you could list your grandfather as Rumplestiltskin JONES, or Bio Father, and that is what TL will report.

Also note that even if all the information in a TL report is correct, there is no guarantee that the identified CA is the Ancestor who passed down the shared DNA segment. As reported here, I found at least 10% had a shared DNA segment that did not come from the CA.

Edit 20190801 *sometimes other “3rd-party” Trees are used to complete the linkage from a Common Ancestor down to you and/or your Match.

[22AO] Segment-ology: How Does ThruLines Work TIDBIT by Jim Bartlett 20190801

A Few ThruLines Are False, and Some are Misleading

A Segment-ology TIDBIT

I made a spreadsheet of my 1,820 ThruLine Matches – to track and analyze them all. I found 86 were questionable (some of those 86 were clearly wrong, and others were iffy – I just didn’t have the information (or time) to sort it out. 86 is roughly 5% of the total, which means I agreed with 95% of my ThruLine Matches. Note a few of my Matches are double counted because they shared more than one Common Ancestor with me.

A high percentage of ThruLine Matches were good, giving me confidence in this tool.

Of my ThruLine Matches, 145 of them had uploaded to GEDmatch (or tested at other companies). I found one of the 145 (1.5%) had a false Shared Segment with me – it didn’t match a Triangulated Group on either side. I also found that 15 of these Matches (10%) with segment info had TG segments with me which were on a different one of my grandparents than the ThruLine Common Ancestor. This is not necessarily an error by ThruLines (the Match is very likely still a genealogy cousin on the ThruLines Common Ancestor), but in each case the DNA Shared Segment indicated we should have another Common Ancestor on a line from one of my other grandparents. Most of the 15 Matches were on the wrong side – the ThruLines Common Ancestor was on one side, and the Shared DNA Segment was on the other side.

So, from this small sample, about 10% of the ThruLines Common Ancestors may be misleading from a genetic (or chromosome mapping) point of view.


[22AK] Segment-ology: A Few ThruLines Are False, and Some are Misleading TIDBIT by Jim Bartlett 20190729e

ThruLines Helps with Y-DNA and mtDNA

A Segment-ology TIDBIT

When ThruLines finds a Common Ancestor between you and a Match, it provides the picture: The Common Ancestor at the top with the line of descent to you and the line of descent to your Match. Click on the left side of your Match’s Profile to open this diagram of descent.

Pay attention to this line of descent to your Match. Is it an unbroken all-male line down to the Match (every man would have the same Y-DNA, including the Common Ancestor), or is it an unbroken all-female line down to the Match’s mother (every person would have the same mtDNA back to the Common Ancestor’s wife (usually also a Common Ancestor)?  I’ve found a number of these cases, some to be very important to my research. Two of my ThruLine Matches carry the mtDNA of two distant female Brick Wall Ancestors. These are generally very hard to find – but it’s obvious from a quick look at the ThruLine diagram. Three of my ThruLine Matches carry the Y-DNA of our Common Ancestors. Sometimes the Match is excited about helping establish the mt or Y DNA haplogroup or “signature” of our Common Ancestor – other Matches couldn’t be bothered… I offer to help the ones willing to test.

And even if the unbroken all-male or all-female line only comes down to the Match’s parent or even to the grandparent – an interested Match may know of close, living relatives who may continue the line and be willing to test. For me, it’s certainly worth mentioning to the Match.

ThruLines may help you find mtDNA or Y-DNA candidates that might be helpful to you.


[22AJ] Segment-ology: ThruLines Helps with Y-DNA and mtDNA TIDBIT by Jim Bartlett 20190729d

Add ThruLines Info Into Match Notes

A Segment-ology TIDBIT

Each Match has a place under the Match name to enter notes into a Notes box. Only you can see these Notes. They can be very helpful. I’ve blogged about them here and here.

I’ve been adding the info from all my ThruLines Matches into the Notes. For example the Notes box may start with:

#A0018P/3C1R: NEWLON/ALLEN > Salathiel

This tells me the Ahnentafel number of the Common Ancestor is 18. In Ahnentafel “speak” this means this Ancestor is related to me: 18 > 9 > 4 > 2 > 1. I am #1, my father is #2, my father’s father is #4, my father’s father’s mother is #9, and her father is #18. I add the “P” for Paternal side because with large Ahnentafel numbers, I lose track which side they are on;>j The 3C1R is shorthand for 3rd cousin once removed. And then I type the two surnames of the Common Ancestor Couple. And I often included descendants on the Match’s side down to an Ancestor in the Match’s Tree – just so I don’t have to reinvent that path later, and to have it handy for my reference. Handy is good when you are dealing with thousands of Matches. Matches with Common Ancestors are usually in short supply (and they are like gold!), so I don’t mind adding a little extra in the Notes about them.

Note: the #A is used to allow searches with the MEDBetterDNA Chrome Extension.

Help yourself by recording ThruLines info in the Notes boxes – they will help you later.


[22AL] Segment-ology: Add ThruLines Info Into Match Notes TIDBIT by Jim Bartlett 20190729

ThruLines and Clusters and Snowballs

A Segment-ology TIDBIT

The process using Match Notes and identifying Clusters (see blog post here) has a snowball effect. Other Matches in the Shared Match list are more likely to have the same ancestry. Check this by clicking on one of those Matches (for whom you don’t yet have a Common Ancestor) and seeing if a lot of their Shared Matches form a Cluster – sometimes they do, sometimes they don’t. Focus on when they do! Focus on Matches who Cluster with several Shared Matches you’ve already connected with the same branch of your Tree. If the target Match has a small Tree, I have often been able to look at the tips of their Tree and recognize a collateral name from my previous research on my Tree branch. Or to find a location that leads me to research and extend a branch of their Tree. Or to add a few more descendants in my own Tree branch…

When a Match has several Shared Matches for whom you’ve already identified the same ancestral line, the probability is high that that Match will tie into the same ancestral line.

Snowball ThruLines to Notes to Shared Matches to Clusters to Common Ancestors with more Matches.


[22AN] Segment-ology: Use Match Notes from ThruLines to identify Clusters TIDBIT by Jim Bartlett 20190729

Use Match Notes from ThruLines to Identify Clusters

A Segment-ology TIDBIT

When you add ThruLine info to a Match’s Notes box, it can be very helpful. When this ThruLine info is the initial entry in the Notes box, it is then visible when viewed in a list of Shared Matches. This makes it easy to scan down a list of Shared Matches and quickly determine if there is a clear thread – a Cluster – there. This is confirming evidence that we are on the right track. And I add a line in my Notes to the effect that X number of other Matches all agree on the same line of my Ancestry.

Type ThruLine info into Match Notes to find Clusters of Matches.


[22AM] Segment-ology: Use Match Notes from ThruLines to identify Clusters TIDBIT by Jim Bartlett 20190729

ThruLines Has X-ray Vision

A Segment-ology TIDBIT

AncestryDNA’s new ThruLines automatically finds Common Ancestor(s) – out to 5xGreat grandparents.

AND, because AncestryDNA can also see the Private Trees, it can find Common Ancestors you cannot see – it’s like ThruLines has X-ray vision! If your Match’s Private Tree is searchable, it will even show you the path to the Common Ancestor (otherwise it will show Private for each generation back to the Common Ancestor). This is a very powerful feature. Many of us complain about all the Private Trees.

Well… now ThruLines looks right into them for us and determines our Common Ancestor(s). ThruLines works to find these Private Matches even when they have small Trees, but have an Ancestor who is also in your Tree as a descendant of one of your Ancestors (see previous post about adding children and grandchildren). If you think you know how a Private Match might be related to you (say, by finding several Shared Matches, all on one of your lines), try adding some more descendants in that part of your Tree and wait a day or two. This also helps in developing larger groups of Shared Matches and identifying more Matches in Clusters.

Use ThruLines to find Common Ancestors with Matches who have Private Trees!


[22AI] Segment-ology: ThruLines Has Xray Vision TIDBIT by Jim Bartlett 20190729