When we compare SNPs on the Y chromosome, we can see which testers share the same mutations and where new mutations created separate paternal branches. Those relationships allow us to build a genetic family tree. It resembles a conventional family tree, but each branch is defined by a SNP rather than by a named individual. A man who tests positive for a downstream SNP will also be positive for every ancestral SNP above it, just as a person descends from his father, grandfather, and earlier paternal ancestors.

The tree below shows the present structure of haplogroup E-Y6923 based largely on Big Y testing. The testers appear at the ends of the branches, while the nodes above them represent the SNPs that define their shared paternal ancestry. Since the project’s earlier tree was created, many additional branches have been discovered. We can now distinguish lineages that separated in antiquity and the early medieval period, as well as much more recent family clusters that developed during the last several centuries.

The current tree reveals that E-Y6923 was not a single undivided lineage until the genealogical period. Important downstream branches were already forming and expanding many centuries ago. E-Y6940, for example, has a surviving common ancestor estimated near 650 CE, and several of its major branches diversified again between roughly 750 and 1000 CE. Later waves of expansion, especially from about 1200 to 1500 CE, may reflect the growth and movement of Ashkenazi communities into eastern Europe and their interaction with older Jewish populations already present in the region. Other branches expanded at different times, perhaps in response to migration, settlement opportunities, population growth, or local historical conditions.

Every new Big Y test can refine this history. A new tester may confirm an existing branch, divide a broad branch into smaller family lines, identify previously unknown shared ancestry, or create an entirely new named branch. Testers who tested years ago with older Y-DNA products may also be able to contribute substantially by upgrading to the current Big Y test. Even a result that appears to fall on a well-established branch can provide the comparison needed to date that branch more accurately or separate two families whose relationship is presently unresolved.

Participation is especially valuable from Testerswith well-documented direct paternal ancestry. A Big Y result combined with a reliable surname line, earliest known paternal ancestor, and place of origin helps connect the genetic tree to actual families and historical communities. The more men who join the project and upgrade, the more precisely we can reconstruct when these branches formed, where they may have developed, and how the many E-Y6923 families are related.