Of Mirroring And Shared Ancestors: Exploiting AncestryDNA To Find Biological Families


What we aim to accomplish in this post:

  1. Provide definitions and an overview of methods for finding biological families of those who don’t know one or both biological parents, using tools at AncestryDNA.
  2. Discuss possible future methods that may be helpful in reaching the same goals.


Finding a bio-ancestor is like finding the horizon on a foggy day - keeping looking and you might find it.

Looking for a bio-parent may feel like looking for the horizon on a foggy day – but keeping looking and you might find what you seek.

Edit 10 May 2016: The May 2016 change in the matching algorithm at AncestryDNA makes some of the details in the PDF out of date, but the basic ideas still apply.

One of the more common uses of autosomal DNA matching products such as 23andMe, AncestryDNA, and FTDNA Family Finder, is for people searching for their biological families, including:

  1. Adoptees searching for their biological ancestors;
  2. Those who discover that one of their presumed biological parents turns out not to be so – often a shocking surprise, but sometimes also a deeply and long held suspicion that turns out to be true;
  3. Those who never knew one or both parents (usually but not always a missing father.)


The processes described here are not new nor invented by me.  An entire community of people dedicated to genetic genealogy and helping others (such as adoptees) have arisen and the methods being used are continually improving, especially as creative software developers bring forward new tools to make use of autosomal DNA matches.

However, on forums and Facebook groups it seems that the same questions get asked continually about finding family using DNA, sometimes posters presenting the same question within minutes of each other. Thus we believe that there is still a need for more educational material on this topic.

In the presentation below, as a PDF file, is an overview of how to exploit one’s DNA test at AncestryDNA, including:

  1. mirror pedigrees;
  2. shared matches;
  3. ancestor harvesting.

This presentation is not an exhaustive exploration of these topics, but hopefully will be helpful to many seeking bio-families.

Data Mining Through Mirroring

Download (PDF, 3.35MB)



I believe there are two possible tool types that AncestryDNA could give us that would help in research, both for more traditional genealogy goals (i.e., finding ancestors beyond those we knew personally) as well as for those searching for birth families:

Surname analysis

See my post “Surnames, 23andMe, and AncestryDNA: Making the Most of Match Counts and “Enrichment”

Geographic analysis

Our ancestors lived in locales at specific times and much family history work depends upon locating our ancestors within their landscape.  Not enough of this is done by novices to family history but often analyzing locations are key to unraveling complex families.  Anyone who has spent some time reviewing family trees knows that the location fields for deaths and births and many of the events in-between are often left off, or given inaccurately.

AncestryDNA does provide a map tool for every DNA match, to see where the match’s ancestors were born, according to the tree to which the DNA kit is attached. This is very useful for my matches where surnames are of little to no use (such as my Norwegian ancestors).  AncestryDNA also provides a filter for searching matches by location.  Both are limited by the difficulties in conforming geographic names to standards, as well as the sad fact that even those of our matches who have family trees often do not have birth locations for their ancestors.

Still, it ought to be possible for an automated process to sort the ancestors of our matches into location groups.  In this regard even the rudimentary Map View in the DNA Relatives tool at 23andMe offers a capability not at AncestryDNA.  For example, there are  3,144 counties (or county equivalents) in the US – why can’t we have a heat map at the county level, for the birth and death counties of the ancestors of our matches?  There are analogous (to the US county system) geographical divisions in many nations that could also be heat-mapped.

In the bigger picture we are discussing what might be called “data mining”. We want to use automated systems to find patterns in large data sets. Here we have two large data sets: DNA matches, and Family Trees.

The collected family histories available both in traditional publications (books, journals, monographs) and electronically represent our families and their culture through the collective historiography work of many thousands of people, some professional genealogists, many of them not.

Connecting this family history to that of our physical inheritance – as presented through our genotypes, created by these direct to consumer DNA testing companies – is the goal of everyone in genetic genealogy.  Of the companies involved, so far AncestryDNA has proven for me and many others to be the most able to reach this goal (though as a product it is still wanting for some basic tools, such as a chromosome browser for those wishing to do segment mapping.)   I’m hoping someday they will add tools in the categories I list above.