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Why Use DNA Testing in Your Genealogical Research
Compiled and written by Jo Roth, WCGS Webmaster and Volunteer


A great amount of family history can be discovered by using the paper trail left by our ancestors, related families, and even their friends and neighbors in our research.  It is exciting to find documents or newspaper articles mentioning the person you are researching and even more exciting to begin to put the puzzle pieces together of the lives they led and how each one fits into the bigger picture of our own histories.  We all know that thrill of discovery!  It is often what keeps us coming back, time after time, staying up until the wee hours of the night, trying to find just one more thing or seeking to prove (or disprove) a theory.

But what if those paper documents don’t tell the whole story?

It is a rare family tree that does not include an unexpected pregnancy or adoption (formal or informal), somewhere in the branches.  Even the early death or disappearance of a biological parent can lead to misinformation down the line as children take on the surnames of the men who raise them.  Regardless of the circumstance, most researchers recognize that there are sometimes two families to trace:  the family found on paper, and the family that is biologically connected through DNA.

DNA testing can tell us more today than ever before.  But before you jump in with both feet, you need to know some basics.

Wikipedia's explanation of Genealogical DNA Test:

What Autosomal DNA Testing Can (and Cannot) Do


Before anyone does a DNA test for genealogical purposes, you have to know that in addition to giving you information about who else you share DNA with (your matches), it may also reveal things you might not anticipate, such as no biological connection to an expected parent, unknown matches (close or otherwise), and ethnicity other than what is believed.  It will not give you the name of an unknown ancestor or prove any relationship further than parent / child or full siblings (all others can have at least one other possibility).  It will not give you the exact relationship to each match, because even if you trace the connection, there could be additional connections that explain the strength of that match.


But by learning how to interpret the information given on each testing site, you CAN narrow down the possibilities of what relationship each match might be.  And while it may not be your original objective, one of the ways you can use DNA matches is to prove who you are NOT related to.


AncestryDNA Learning Hub on “What is Autosomal DNA Testing?”:


For more information about DNA Testing Limitations:

Types of DNA Tests


There are three main types of DNA tests used in genealogy:  Y-DNA, mtDNA, and autosomal.  AncestryDNA explains the differences between them:

For most, taking an autosomal DNA test is the best place to start.  If you want to test with the company that has the biggest pool of testers, then you need to test at AncestryDNA.  The good news is, they have sales from time to time, and once you receive your results, you can download the zip file to your computer and upload it to some of the other sites.


Downloading DNA Data from AncestryDNA:


Diahan Southard, Your DNA Guide, on which DNA test to take:


She also has a good article on “How to Take a DNA Test if You Can’t Spit”:


AncestryDNA Learning Hub on “5 Things to Think About When Selecting a DNA Testing Kit”:


Diahan Southard, Your DNA Guide, on “Create a DNA Testing Plan”:


Judy Russell, The Legal Genealogist, on the sales during the Fall of 2021:


ISOGG (International Society of Genetic Genealogy) – Autosomal DNA Testing Comparison Chart:


Another consideration before you decide to implement DNA testing is what happens to this information when you are gone?  Judy Russell, The Legal Genealogist, on having an estate plan:

What to Do While You Wait for Your Results


While you are waiting for your results, it's a great time to learn as much as possible, so you will know what you are looking at once they arrive.  Terminology is a good starting point.

Centimorgan, which is abbreviated cM, is a term used to measure the strength of your DNA matches.  Diahan Southard explains:

What is a Centimorgan | Centimorgans Explained (5 Apr 2021)

FamilyTree Magazine has a comprehensive list of terms commonly used in Genetic Genealogy and a free download, if you are interested:

Another very important thing to do is to get your family tree DNA ready.  Concentrate on making that tree wider, not taller!  Add in siblings, aunts, uncle, and cousins.  This really does help you get better information when your results come back.  Having an online tree at, FamilyTreeDNA, or MyHeritage is also recommended.  Diahan Southard on the Best Family Tree for DNA Matches:

Understanding Your Results
Ethnicity Results


Ethnicity results are estimates based on the data that has been collected to a certain point in time.  As more data is collected, it may cause your ethnicity estimates to change.  It's not that YOUR DNA changed, it's that the data that has been collected has increased, causing the estimate being given to you to change.  

One question that we often hear is how can I not show any ethnicity from _____ (fill in the ethnicity of your choice), when I KNOW my ancestors came from there?  It is completely reliant on what DNA was passed down to you.

Judy Russell, The Legal Genealogist, on recombination:


Below is the link to the Shared cM Project.  If you look at the block for Self and then track to the right, you will see that you absolutely WILL match a 1C or 2C at some level.  But starting at 3C, the lower end can be 0.  This is commonly seen when looking at match lists for siblings.  For example, one sibling may match a specific person at a level that would be considered high and the other sibling(s) may not match that same specific person at all.  It's a really good reason to test several individuals, second cousins being ideal.


This does a pretty good job of explaining it (I just hate all the ads on this site):


Blaine Bettinger also does a good job of explaining how these tests are just estimates:


And Kathy Reed does a GREAT job of explaining ethnicity estimates in this video:

DNA Matches

While all the information we get as part of our DNA test results is interesting, the list of DNA Matches is, for many genealogists, the reason we are here.  It is a list of people who are SOMEHOW biologically connected to you and the starting point for figuring out where they fit in your family tree.


Understanding How You Are Related to Your DNA Matches

Diahan Southard explains how you can find this information at the different testing sites.


Cousin Chart – Family Relationships Explained

A wonderful blog post on that explains cousin relationships.  Includes links to download the Cousin Chart and Cousin Calculator.


Shared cM Project 4.0 tool v4 beta

An interactive tool developed by Jonny Perl at DNA Painter and Blaine Bettinger that allows input of cM to show possible relationships and statistical probabilities of each possible relationship.


More about the tool:


There are a number of approaches to your list of DNA matches, but HOW you approach that list often depends on WHAT information you are trying to find.  If you are just wanting to work through your list and see how each one fits into your tree, it will take time, and you may be stumped by people who appear NOT to connect based on the paper trail you find or the family tree they have posted online.

One of the best approaches to working with your matches is to divide them into groups, marking them along the way.  Dana Leeds developed The Leeds Method of dividing your matches based on who they match, creating groups that should trace back to a common ancestor or ancestral couple.  It is a GREAT approach, and not difficult to do, whether you are using an Excel spreadsheet or the dots provided online at Ancestry.  More specifics on The Leeds Method:


It is still easy to get overwhelmed with the sheer number of matches and the amount of time it takes to figure each one out.  For some, starting with the ones you know works best.  Call it the low-hanging fruit method.  This gives you some practice working through the process while looking at people with whom you are familiar and makes it a little easier when you start to work on someone that you do not know or understand how they connect to you.  Diahan Southard on how to Link Your DNA Matches to Family Trees:

What if You Need More?

The best advice is to not quit and definitely, don't give up! Keep watching webinars, taking classes, and reading everything you can find on the subject.  Using DNA in genealogy is a complicated subject and can be extremely frustrating at first.

There are many very knowledgeable people from whom you can learn more.  The list below includes just a few, but they are the ones I learned the MOST from.  DNA research has become my passion and I never tire of the never-ending task of building trees for matches!

The buttons below will take you to a summary sheet about each person highlighted in this section, which includes links to their websites, Facebook pages or groups, webinars, etc.


If you are a BEGINNER, I cannot say enough about Diahan Southard and her team at YourDNAGuide.  Her classes and webinars are stellar and put in simple enough terms that it's not so overwhelming.  Having said that, she moves at a very fast pace!  Rewind and listen again and again until you understand the concept she is discussing.


If you are past the beginner stage, but not quite an expert yet, you may find Blaine Bettinger to be another great resource.  He is considered one of the pioneers in this field and has some incredible webinars online, including the very popular five-part "Foundations in DNA" series on Legacy Family Tree Webinars.


Leah Larkin is another such pioneer.  Founder and Lead Genetic Genealogist at The DNA Geek, she has a fantastic blog!  Leah has done some great webinars and always has interesting discussions on her Facebook page, which has a focus on using genealogical DNA results to help adoptees and others find their biological families.


CeCe Moore is incredible.  While she can get a beginner fired up and ready to tackle this subject, her mind is so fast that she is able to make connections with little effort and beginners don't always see what she sees.  This can be frustrating, so you may not want to start with her, but definitely include her in your lineup after you have learned the basics.  She has a podcast starting Spring 2022 and is speaking at I4GG (Institute for Genetic Genealogy) in April 2022.


If you are ADVANCED, it's time to start implementing some of the online tools that are available, such as DNA Painter.  Jonny Perl has some great videos on using the tools found there that can help you work with your DNA test results.


You may also be interested in The Journal of Genetic Genealogy, and can subscribe for FREE here:

Last, but not least, Hamilton County Genealogical Society sponsors the Southwest Ohio DNA Interest Group and they have many of their presentations online:



Using DNA in genealogy is an everchanging field, and there are many more speakers, instructors, interest groups, tools, and programs than listed here.  If you have any questions or feedback, are interested in learning more about something that is NOT covered here, or would be willing to write or contribute a section or profile page, please contact me using the form on the About Us page.  I am always happy to hear from others on the subject of DNA!


Jo Roth, WCGS Webmaster and Volunteer

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