Using DNA Tests to Identify an Unknown Biological Parent

Written By Heidi Buck

Many people turn to DNA testing because part of their family story is missing. In some cases, that missing piece is a biological parent. Over the past several years, I have worked with clients who faced this exact question, using AncestryDNA results alongside traditional genealogical research to reach well-supported answers.

This kind of work combines genetic evidence with historical context. DNA points the way, but records and analysis are what turn those signals into a clear conclusion. Below is the general approach I use.

Starting with the DNA matches

I begin with the client’s DNA match list because it quickly shows how complex the case may be. When close relatives, such as first cousins or closer, appear on the unknown parent’s side, the path forward is often more direct. These matches provide strong anchors that allow the research to expand outward with confidence.

When matches are more distant, the work requires more time and structure. Even so, as long as several matches can be connected to the same ancestral lines, the case can still be solved. The key is identifying shared relationships rather than focusing on any single match in isolation.

Building the known-side tree

Before turning fully to the unknown parent, I build out the client’s tree for the known parent. This usually includes parents, grandparents, and extended relatives.

This step serves two purposes. It helps separate which DNA matches belong to the known side, and it establishes important context. Where the known parent lived, who they interacted with, and what was happening in their life at the time all matter when interpreting DNA evidence.

Adding personal and historical context

Once the known-side structure is clear, I incorporate details the client can share. These often include where they were born, the ages and circumstances of their parents at the time, possible locations tied to conception, and any family stories, even those that seem minor.

This information becomes critical later. DNA alone cannot confirm timelines or life circumstances. Context helps narrow possibilities and evaluate which candidates truly fit the evidence.

Isolating the unknown-side matches

After accounting for known-side relatives, the remaining matches belong to the unknown parent’s side. These matches become the focus of analysis.

At this stage, I create small working trees for each relevant match. These trees are not meant to be exhaustive. Their purpose is to connect matches to one another, identify recurring surnames, trace shared ancestors, and spot overlapping locations. As these connections emerge, a distinct family group begins to take shape.

Expanding the cluster

As more match trees are connected, the goal is to form a larger cluster that traces back to shared ancestors. Patterns begin to appear naturally. Surnames recur, relationship ranges make sense, locations align, and timelines begin to converge.

Once the cluster is strong enough, it provides the framework needed to identify the biological parent. After confirmation, that side of the tree can be built out more completely and documented in detail.

Narrowing to the most likely parent

The final stage combines DNA evidence with real-world records. I compare the client’s birth details with candidate timelines, ages, and locations. I also review vital records, public documents, and other available sources to confirm whether each candidate fits both genetically and historically.

In many cases, this step brings clarity. The correct parent stands out because the DNA, records, and context all point to the same conclusion.

Bringing the story together

Identifying an unknown biological parent is rarely simple, but modern DNA testing has made it far more achievable than it once was. When genetic matches are evaluated carefully and placed within a solid genealogical framework, the evidence begins to align.

DNA provides the signals. Genealogy turns those signals into a documented family story.

If you are facing a similar question in your own research and would like help working through it please look at my professional services page where I offer DNA analysis assistance.

Additional tools and references

Heidi Buck
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