DNA Genealogy

DNA is useful in genealogy. From adding previously unknown relatives to your family tree, to making new discoveries not mentioned in the written record, to breaking through family tree brick walls, DNA research is a great addition to a family historian’s toolkit. I described my genealogy breakthroughs in my book Discover Your Roots! How I found my North American and Revolutionary War Ancestors. Some of those genealogy breakthroughs involved DNA.

Many people join a DNA site to get their ethnicity results, but those results are inconclusive and just scratch the surface of what can be discovered. My experience is that the sites have different procedures for calculating ethnicity and so ethnicity results vary from site to site. My ethnicity results were different for all three of the sites mentioned below.

If the user’s goal matches the focus of the DNA site, the site can provide information that is helpful. The DNA sites below also vary in utility for genealogy purposes. The specializations of the sites are a mixture of health, genealogy and ancient genealogy roots.


Hoping to break through my family tree surname brick wall I joined 23andMe. Their website is useful for DNA related health information but their family tree facility is not as useful.  The site also shows a list of the user’s cousins. That list would be more actionable if more members posted family tree information.

 What was most useful for me was that 23andMe gave me my male and female haplotypes. Haplotypes are that portion of DNA passed on relatively unchanged as generations flow through the centuries. 23andMe provides the user with detailed haplotypes as part of its basic service. Those haplotypes led me to the next DNA website FamilyTreeDNA.com and its family surname projects. 23andMe also has a chromosome browser making it possible for members to compare DNA links with their cousins.

Chromosome browsers are good for visualizing DNA intersections with potential cousins. See below for a 23andme illustration that appeared in the book by Bryan Sykes, DNA USA A Genetic Portrait of America, for an example of a chromosome browser charting functional gene locations.[1]

Example Chromosome Browser


My male haplotype is shared with two famous inventor brothers, my distant cousins, who have a well-documented family tree going far back in English history. They appear in a section of a family surname YDNA project on the FamilyTreeDNA site. Prior to my joining the project everything prior to the 1790 census for my surname was a mystery. With information provided by the project I was able to break through my surname brick wall.[2]

FamilyTreeDNA also has a fascinating new YDNA facility called Discover that shows ancient YDNA connections that are linked to the user’s YDNA. Those connections are derived from archaeological investigations performed at archaeological dig locations all over the world. 

FamilyTreeDNA has a chromosome browser that can be used to compare autosomal DNA chromosome by chromosome between several users at a time. Autosomal DNA is inherited half from each parent. The site prompts users to include their family trees but most of the trees that I’ve seen on the site are not well done. A lack of good family trees and weak presentation of those trees limits the usefulness of the chromosome browser.

AncestryDNA at Ancestry.com

FamilyTreeDNA and 23andMe are limited by the size of their customer base. Both have fewer customers than their competitor AncestryDNA. AncestryDNA has a large customer base, exceeding 20 million users.

Similar to 23andMe and FamilyTreeDNA many AncestryDNA users do not post a family tree. Most probably are unaware that with a minimum amount of effort even inexperienced users could quickly research the linked trees of DNA relatives and use Ancestry’s hint facility to extend their knowledge of their family far back in time.

AncestryDNA does not provide haplotypes. It also does not have a chromosome browser. Instead it has a facility called ThruLines that plucks linked ancestors from other member’s trees and presents those shared ancestor results to the user for evaluation. Those results may be accurate or inaccurate depending on whether the trees from which the ancestor has been plucked are accurate or inaccurate, which leads to the next conundrum.

Many users on Ancestry that have trees do not do their own work but merely copy the work in other trees without checking for accuracy. Copying the trees of other users without checking their accuracy multiplies the number of inaccuracies in the AncestryDNA database and probably promotes the likelihood of seeing an inaccurate potential shared ancestor presented in the ThruLines facility of AncestryDNA.

I say ‘probably’ because ThruLines is a black-box procedure that takes inputs and through some unexplained process crunches the inputs and produces an output.  Ancestry.com explains that ThruLines draws matching ancestors from other user’s trees. Using Hadoop, ThruLines matches strings of DNA in order to present potential ancestors. The problem is that AncestryDNA does not fully share what is going on in that black-box.[3]

Hadoop, sometimes called ‘Big Data’, is the computer process that breaks up a complex problem involving large databases into multiple components, using many computers to find solutions to each component. Hadoop then reassembles the various solutions to answer the complex problem that was first posed.

It is left to the user to determine whether the AncestryDNA ThruLines match produced by the Hadoop process is accurate or not. ThruLines also shows a list of users that both matches share, although there is no indication that the users on that match list share the same ancestor. Clearly, somewhere in the ThruLines black-box triangulation is occurring.

Triangulation is the occurrence of shared DNA in the same location of the same chromosome between three or more users. Chromosome browsers such as those available with 23andMe and FamilyTreeDNA show the location of shared DNA on a chromosome chart and add a layer of certainty to a hypothesized family relationship between users. AncestryDNA has the number and quality of family trees required to make triangulation a useful tool for most members.

Without a chromosome browser AncestryDNA users can only search for similar surnames in cousin trees, then look through those trees to see if similar ancestors to those of the hypothesized ancestor appear with adequate documentation in the tree being researched. Such a search takes time and effort. Users are left to guess if adding more descendants of the hypothesized ancestor to their own tree is a worthwhile endeavor that will result in more matches to their DNA cousins.

That is exactly the process that I followed in researching the parentage of Marietta Williams described in an earlier blog on this site. Using my DNA matches on AncestryDNA I located cousins with well-documented trees containing exact matches to ancestors of both of her parents. I followed a similar process in finding the parents of Elizabeth McLain.[4]

However, given the enormous customer base of AncestryDNA it is possible though unlikely that these cousins are related in some other unknown way. If AncestryDNA included a chromosome browser and better explained what is going on in the ThruLines black-box the accuracy of proposed ThruLines matches and shared matches could be better understood and validated.


DNA is useful in genealogy. The three major DNA services have different specialties and from a genealogical researcher’s perspective all of the services could be improved. However, by combining membership at all three services with a lot of elbow grease the user can assemble a fascinating, multifaceted and very useful amount of genealogy information.

[1] Bryan Sykes, DNA USA A Genetic Portrait of America, illustration plate ante p.275, Liveright Publishing, NY, NY, 2012.

[2] Bruce Wright, Discover Your Roots! How I Found my North American and Revolutionary War Ancestors, p.14-17, p.143-155, Kindle Direct Publishing, 2018.

[3] C. Ball et al, AncestryDNA Matching White Paper, p.9, July 15, 2020. Last accessed 25 Oct. 2022. https://www.ancestrycdn.com/support/us/2020/07/2020whitepaper.pdf

[4] Bruce Wright, Discover Your Roots! How I Found my North American and Revolutionary War Ancestors, Part Two, p.9-16, Kindle Direct Publishing, 2020.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s