Aaron Tassin, MLIS

When Marie first reached out to me, she carried a quiet but lifelong question: who was her biological father? She wasn’t looking for rumor, family mythology, or guesswork. She wanted evidence. She wanted something that could stand up to scrutiny — something genetic genealogy is uniquely positioned to provide. My role was to follow the DNA, interpret what it was saying, and build a case strong enough that the conclusion would feel solid, not speculative.

We began where these journeys often begin — with autosomal DNA, or atDNA. Marie already had test results and a handful of matches. One of the earlier ones shared 117.9 centimorgans, with an estimated Most Recent Common Ancestor (MRCA) of about 3.5 generations back. That amount of shared DNA doesn’t point to a parent, but it does whisper something important: you belong to this family network. The key in cases like this is never a single match. It is the pattern that forms when many matches begin telling the same story.

As I examined Marie’s match list, I noticed that several of her stronger matches clustered around the same 19th-century ancestral couple. Their shared DNA ranged from just over 90 cM to well above 300 cM, with MRCAs estimated at about 2.7-3.7 generations. That’s not random noise. That is a genetic neighborhood. These people were not simply connected to Marie—they were connected to one another, and their documented family trees converged on the same ancestral pair.

One match stood out in a subtle but important way: this person descended from a sibling of one of the key ancestral figures, not from the direct line others shared. That detail helped anchor the MRCA further back, confirming that Marie’s shared ancestry wasn’t coming through only one child of that couple, but through the broader sibling group. In other words, Marie’s DNA tied her securely to that extended family line. We now knew where in the tree her father’s roots had to be planted. What we did not yet know was which branch led to him.

The case shifted from interesting to focused when Marie matched someone at 409 cM across 21 segments. That amount of shared DNA lands squarely in the range of a first cousin once removed. Practically speaking, this meant the match was almost certainly a first cousin to one of Marie’s parents. This was no distant echo from the 1800s. This was recent, close kinship. The genetic spotlight had moved forward several generations and narrowed dramatically.

I built out this match’s family tree. His father was one of three sons born to a couple in the early 20th century, and the mother in that couple was herself a daughter from the same ancestral line we had already identified through Marie’s other matches. The larger ancestral cluster and this close modern match fit together like two halves of the same map. If Marie shared a 1C1R relationship with this man, then one of her parents had to be a sibling — full or half — to his father. Given what we knew about Marie’s maternal background, the implication was clear: this connection was coming through her biological father.

Then came another powerful piece of evidence. Marie matched a second individual at 580 cM, again across 21 segments — a very strong first-cousin-once-removed level. When I examined this person’s lineage, the connection led not through the sons of that same couple, but through the wife’s family of origin. She was a niece of that mother. Now the picture sharpened even further. Marie wasn’t just matching one side of that household — she matched both. Genetically, she sat exactly where a child of one of that couple’s sons should sit.

At this point, the evidence was no longer loose threads. It was a woven structure. Two independent matches at 1C1R levels, each tied to different sides of the same parental pair, required that one of Marie’s parents be a child of that couple. Her many matches to descendants of the earlier ancestral pair explained how the wife fit into the larger pedigree. The cM values, segment counts, predicted relationships, and family trees all agreed. Nothing pointed elsewhere with comparable strength.

Three sons in that family could, biologically, have been Marie’s father. Here, personal history entered the conversation—not as proof, but as context to test against the genetic framework. Marie’s mother stated that she had sexual intercourse with one of those sons during the time period consistent with Marie’s conception, and not with the others. Memory alone is not evidence, but in this case, it did not conflict with the DNA. Instead, it narrowed the focus within a family already defined by genetics.

Still, responsible genealogical practice requires confirmation whenever possible. My conclusion was not a dramatic proclamation, but a carefully reasoned position: Marie’s biological father came from that sibling group, and the most likely candidate was the son identified by her mother. The DNA did not merely suggest a surname or a distant line. It placed her squarely in a specific household.

From there, I outlined the next steps. The most direct approach would be to obtain atDNA from one or more of the six children of that couple, with priority given to the man identified. A test from him—or a full sibling—could confirm the relationship definitively through shared cM levels expected for parent-child or half-sibling relationships.

I also recommended testing Marie’s mother. Doing so would help separate maternal from paternal matches and confirm that the paternal cluster did not come through her. An mtDNA test, while not directly relevant to the father question, would preserve valuable information for future maternal-line research.

Finally, testing a known half-sibling through Marie’s mother would serve as another control, confirming they share the same mother while demonstrating that the paternal cluster is unique to Marie. Together, these steps would transform a strong genetic case into certainty.

In the end, this investigation was not about a single dramatic discovery. It was about listening carefully as multiple pieces of DNA evidence told the same story from different angles. My role was to translate that story — from centimorgans and MRCAs into family relationships and human meaning. For Marie, the question that once felt like an absence had become a clearly defined branch of a family tree, illuminated not by guesswork but by the quiet, consistent language of genetics.

Portions of this post and the image of Marie were produced with the assistance of LLM GPT-5 from my own detailed, reiterative prompts. Marie is not my former client’s true name.