What type of a relationship with an ancient person does a shared DNA fragment imply?

In 2022, we reported the DNA sequences of 33 medieval people buried in a Jewish cemetery in Germany. Not long after we made the data publicly available, people started comparing their own DNA with that of the 14th-century ...

But what type of a relationship with a medieval person does a shared DNA fragment imply? It turns out, not too much that will help with your family roots research. We are population geneticists who work with ancient DNA . We understand how exciting it can be to find a genetic link to particular people who lived many generations ago. But these DNA matches aren't the tight ties you may be imagining. Here's how it works. Sequencing DNA from those who lived long ago Ancient DNA is a new and rapidly growing field, with a Nobel Prize awarded in 2022 to Svante Pääbo for his foundational work.

Using samples taken from skull bones or teeth, aDNA researchers can sequence the DNA of people who lived as far back as 100,000 years ago. More than 10,000 ancient DNA sequences , or genomes, are currently available. These genomes, which come from all corners of the world, have dramatically revolutionized scientists' understanding of human origins . A new trend in ancient DNA is sequencing the genomes of "historical" individuals: those who have lived during the past millennium.

A comparison of one chromosome’s DNA sequence between a 14th-century German Jew and two living people who uploaded their DNA to GEDmatch. Each thin vertical bar represents one letter in the DNA sequence and is color-coded based on whether it is a match. A shared DNA fragment appears between living person 1 and the medieval person. Credit: GEDMatch Read more

The red dot at generation 0 represents a present-day person in a simulated population of 100,000 people. Each tiny red dot represents one person, and the red lines connect people to their parents. Ancestors reached through multiple lines in the family tree are marked in black circles. The number of lines becomes so large so quickly that beyond 15 generations ago, most ancestors are reached by multiple lines. Credit: Graham Coop Read more

For someone alive today, the number of genealogical ancestors doubles each generation. But each DNA fragment (colored bars) is inherited through a random, zigzagging path up the family tree, meaning DNA is inherited only from a small fraction of one’s ancestors. Credit: Shai Carmi, CC BY-ND Read more