If you’re not using genetic networks to evaluate your autosomal DNA matches, then you’re missing opportunities to efficiently mine your matches for ancestral clues.
Reviewing your DNA matches can be overwhelming, and it can quickly become daunting to use them to confidently build out your family tree. But it doesn’t have to be this way if you know how to use genetic networks. This seven-part blog series covers the following topics:
- Genetic networks defined (part 1).
- Inclusion and exclusion criteria for genetic network membership (part 2).
- Find genetic networks in your list of matches (part 3, coming Sept. 23).
- Efficiently review your matches’ family trees within a genetic network (part 4, coming Sept. 30).
- Use the Ancestry Pro Tools’ Enhanced Shared Matches feature to group genetic network members into clusters (part 5, coming Oct. 7).
- Find the same genetic networks across multiple DNA websites (Part 6, coming Oct. 14).
- Strategically move from DNA analysis to documentary research (Part 7, coming Oct. 21).
Genetic Networks Defined
Simply stated, genetic networks are a group of people who share DNA. With respect to genetic genealogy, genetic networks are a group of DNA matches that a test taker shares with another match where most of the shared matches in the group have an ancestor in common with one another.
Consider the diagram below where you are the test taker (labeled A) who has taken an autosomal DNA test such as those offered by Ancestry, MyHeritage, FamilyTreeDNA, or 23andMe. When reviewing a particular match (B), most testing websites permit you to view the other matches (C) who also match the same individual (B) you’re currently viewing. Within DNA databases, these “C” matches are identified or discovered via their Shared Matches (Ancestry, LivingDNA, and MyHeritage), In Common With (FamilyTreeDNA), or Relatives in Common (23andMe) filters. To maintain common terminology in the post, I call these “C” matches “shared matches”. In this example, you as the test taker (A), the viewed match (B), and most of the shared matches (C) are what comprises the genetic network.
Membership in the Genetic Network
The assumption is that you (A) and the match (B) you’re viewing share a common ancestor. For example, if I’m viewing the match with a second cousin on a DNA testing website, the cousin (B) and I (A), who are represented below at generation one, share a set of great grandparents in yellow at generation four. Our respective yellow lines represent how we inherited the same DNA segments from the great grandparents. This A-B relationship is the beginning of the genetic network formation.
To visualize a genetic network for any of your matches, click the shared matches filter or similar functionality used in a testing website. The matches that are subsequently displayed (labeled as C) now form the genetic network between yourself (A) and a cousin (B). Within Ancestry, the image below demonstrates how this might look (matches are anonymized).
Displayed another way, as a vertical ancestor family tree, the genetic network can be visualized in the image below. Here, the autosomal DNA tester is shown at the bottom in yellow as “A”. The match being viewed is shown to the right as “B”. While viewing match “B” and selecting the shared filter, this action produces several shared matches, which are labeled as C1, C2, and C3. In this image, the genetic network is comprised of A (you the DNA tester), B (viewed match), C1, C2, and C3 (shared matches).
Within genetic networks, the number of shared matches (C) can vary from as few as one or as many shared matches found within your list of matches. I categorize the shared matches (C) into three groups based on their relationship to the common ancestor or ancestral couple between the tester (A) and the viewed match (B).
Some members of the genetic network are descendant cousins (labeled as C1 in the above image), who share a common ancestor more recently than the common ancestor between the tester (A) and the viewed match (B). These shared matches are called descendant cousins because they descend through the same child line of the common ancestor as the tester (A). Descendant cousin type of matches typically share more DNA with the tester than with the viewed match (B) as measured in centimorgans (cM). They may also share more segments than the viewed match (B) because you have more ancestors in common and thus more shared DNA.
Other members of the genetic network may be lateral cousins (C2), who share only the earliest common ancestor that the tester (A) shares with the viewed match (B). These shared matches are called lateral cousins because they descend from a different child line of the common ancestor than do both “A” and “B”. Lateral cousin type of matches may be at the same cousin level or a generation or two removed from the tester. The amount of shared DNA in cM and segments can vary greatly between lateral cousins (C2) and the viewed match (B).
Finally, other members of the genetic network are ancestral cousins (C3), who share a common ancestor in generations further back in the family tree from the earliest common ancestor of “A” and “B”. These shared matches are called ancestral cousins because their common ancestor with the test taker (A) is more distant than it is between “A” and “B’s” common ancestor, and their connection is through one of the ancestors of the common ancestor of “A” and “B”. Ancestral cousin type of matches typically share less DNA and segments than descendant (C1) and lateral (C2) cousins, although this can vary as well depending on the number of generations removed a C3 cousin is from the tester and the randomness by which DNA is inherited from earlier ancestors.
Genetic Network Examples
In previous blog posts and published research reports, I have presented several examples for how genetic networks can be used to discover previously unknown ancestors. Some of the examples are for ancestors from more recent generations while others are further back in the 1700s.
To conserve space, I summarize each of the examples below. Interested readers are encouraged to click on the blog or research report link to see how I used genetic networks in practice as part of a proof argument for an unknown ancestor. Perhaps the best examples are in the “Ancestral Origins of John Wilson” report, where I was able to use segment triangulation, and the “Father of Mary (McMasters) Boyd” report, where I used multiple DNA testers to identify several relevant genetic networks to find an unknown 18th century ancestor.
The Ancestral Origins of John Wilson
Genetic networks were used here to identify relevant matches tying John Wilson’s ancestral homeland to County Fermanagh in Northern Ireland. Segment triangulation, Y-DNA, and documentary evidence completed the analysis. John Wilson immigrated to the U.S. about 1740. See pages 14-25 in the research report.
- Blog Post. Identifying John Wilson’s Irish Origins, Part 2: Autosomal DNA Analysis
- Research Report. The Ancestral Origins of John Wilson, who died 1799
- Research Like A Pro® Genealogy Podcast #198. Identifying John Wilson Part 1
The Father of Mary (McMasters) Boyd
Seven genetic networks were found among 32 testers who descend from Mary (McMasters) Boyd (1755-1832) and from one descendant of Mary’s brother, Robert McMasters. Along with other evidence, results suggest her father was likely Thomas McMasters. See pages 14-19 of the research report.
- Research Report. The Father of Mary (McMasters) Boyd (1755-1832)
Other Blog Post Examples
- Establish when matches below 15 cM can be used as evidence within genetic networks: Small DNA Matches as a Compass in Genetic Networks. Also, a companion YouTube Learning Module is available.
- Overview of the EGGOS (earliest generation group of siblings) Search Strategy to find relevant genetic networks: Breaking Through 18th and 19th Century Brick Walls: ‘Don’t Let Go of Your EGGOS’. Also, a companion YouTube Learning Module is available.
- Demonstration for the combined use of genetic networks and documentary research to discover unknown ancestors: Genealogy Ping Pong: Alternating Between Documentary Research and DNA.
- Using Google Maps and genetic networks to identify a previously unknown grandparent: DNA and Google Maps: Breaking Through Brick Walls to Reveal a Love Story.
Conclusion
You might have noticed that earlier in this post I qualified shared matches (C) to say that “most” shared matches will be members of the genetic network who share a common ancestor with both “A” and “B”. In part 2 of the blog series, I’ll explain why some shared matches in the produced list of “C” matches are not true members of A and B’s genetic network.
Click the following link to read Part 2 of this blog series, How to Identify Misclassified Members.
Acknowledgment: The image used within the header at the top of the blog post was created using Microsoft’s Copilot AI-powered assistant (DALL-E 3) and added to the title slide. AI tools were not used to generate the blog’s intellectual content or provide writing assistance. The post was authored solely by me.
Thank you for this.