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  • Writer's pictureTheFormidableGenealogist


Updated: Jun 9, 2023

I've typed this into client correspondence several times over the last couple of weeks, so I thought it might be a good subject to blog about.

The ThruLines feature at is a great tool that I use all the time. It fills in family tree information for DNA matches who have incomplete trees, so it can be a shortcut to identifying how a DNA match relates to you (or the person whose DNA sample you're managing).

"Since ThruLines are based on the family trees of you and other members of Ancestry, they're as accurate as the trees they're based on. Mistakes in family trees can cause inaccurate ThruLines.

Because they're based on trees, ThruLines don't prove your specific connection to a DNA match...."

Those are the company's words, but I've added the emphasis. I think many people who are looking at ThruLines to prove relationships and solve family mysteries aren't aware of that. Therefore, they aren't doing an essential part of the process, which is analyzing how the descendants of a potential ancestor relate to the sample and each other. That is complicated and can't be summed up in a single blog post, but I can at least share some tips for anyone using the Ancestry ThruLines feature.

  • ThruLines may be incorrect if there is incorrect information in multiple family trees. An example is a distant ancestor of mine. John Jacob Baugher was born in 1760. His wife, and the mother of all his many children, is identified in hundreds of family trees as Sarah Ledbetter. Based on his age when his younger children were born, I suspect that John Jacob had children with more than one wife. The woman he was married to at the end of his lifetime was a Sarah, but there is no evidence that she was the mother of the son of John Jacob who was my ancestor. There is absolutely no primary source evidence that Sarah's name was Ledbetter. I know where the error came from, but it's incorrect. And it persists. That's a long story of how ThruLines tells me that my 5th-great-grandmother is Sarah Ledbetter. She is not, and Sarah Ledbetter may not have been a person at all. But ThruLines tells me that she is because that information exists in so many other family trees.

  • ThruLines may suggest the way you're related to a DNA match, but that isn't necessarily the way you are related to that match. ThruLines is going to find the easiest explanation based on information that is already input into family trees. If the true genetic connection to a match is by way of ancestors who are not in your tree or the tree of that match, ThruLines might not catch it. Instead, the tool would find another pathway of relationship. In that case, the DNA from that ThruLines ancestor might not be the DNA you actually share with that match. Misunderstanding the true relationship can result in using incorrect data to support a relationship or theory. That is true when trying to explain closer genetic relationships, and it gets increasingly complicated with each earlier generation.

  • ThruLines may disregard true genetic relationships. My 3rd-great-grandmother Rebecca has a father whose name is unknown to us. Most family trees don't have the correct mother for her, either. Neither do any of them realize that she had a brother. In every family tree I have seen for this brother George, he is attached to the wrong parents. I have the proof that these two are siblings. However, none of George's descendants is going to find it unless they recognize their tree is wrong and seek out the information. Until then, the data for the George in my tree appears in no other family trees. That means that ThruLines doesn't recognize George as part of my family. That means that the dozens of my DNA cousins who descend from George are not included in my ThruLines. I've independently identified these DNA cousins, so that I can try to use the shared matches with them to identify Rebecca and George's father's family. However, that task would have been much easier if there had been a short-cut to those relatives. And--more importantly--the lack of a ThruLines connections to an ancestor is not proof that you aren't related to that ancestor.

  • ThruLines may not recognize the same person as being the same person. If the person's name, dates, or location varies across trees, ThruLines may not recognize that. This is another way in which DNA connections might be missing for a certain ancestor when you know or think there should be some.

  • ThruLines can be easily manipulated. I frequently put incorrect data into the family tree attached to a DNA sample in order to manipulate ThruLines into testing theories for me. (Lazy, or efficient? You decide.) If I can identify descendants of a particular person or couple, I can more quickly analyze the genetic connections and hopefully figure out where to search next. Whatever garbage data I input, ThruLines will get to work trying to figure out which of my DNA relatives descend from that couple. Whether I'm related to those people or not. In a future post, I'll share an example of doing that, and the results.

Again: ThruLines is a great tool, and I use it all the time. It's helped me countless times to test theories, gather clues, and develop research plans for the documentary component of genetic genealogy.

For other users--it's a great tool, but you should know how it works. Relying solely on it or not understanding it can cause more harm than good in your family history research.


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