Genetic Genealogy Testing 101—The Who, What, Where & Why

Guest Authored by Paul Woodbury, Senior Genealogist, Legacy Tree Genealogists

DNA is such a hot topic in ancestry and genealogy research lately. Have you taken a DNA test? Did you take the standard test or did you take one that goes deeper into the results?

I recently conducted a blog interview with Legacy Tree Genealogists and they have provided this blog to explain what genetic genealogy testing is and how to understand the results.

In the future, genetic testing will become an increasingly integral part of the fields of family history and genealogy. Even now, genetic testing is sometimes considered necessary as part of the reasonably exhaustive search required for the genealogical proof standard.

In this introduction to DNA testing for family history purposes, we’ll outline how DNA tests work, provide an explanation of the tests available and the companies that offer them, and finally, explain what results you can expect and how they can be used to answer family history questions.

DNA Testing Companies


There are three main companies that offer tests which are useful for family history. In order for a DNA test to be useful for genealogical investigation, it must analyze informative markers on the DNA and it must connect the results to a database of other tested individuals. Although there are many companies that offer DNA testing for some type of ancestry analysis, only three of these companies meet the aforementioned criteria:, Family Tree DNA, and 23andMe.

Taking the Test

Each of these companies uses similar collection methods. After a customer purchases a test, they will receive a kit in the mail. Both and 23andMe use a saliva collection tube, whereas FamilyTreeDNA uses a cheek swab. These non-invasive collection kits do not require the subject to draw blood. They are simple to use and come with a detailed set of instructions.

23andMe and require the creation of an account in order for the test to be fully processed. FamilyTreeDNA will request an email address where the results can be sent.

DNA Test Types

There are three types of tests offered for family history purposes.

  1. Y-chromosome which is offered by FamilyTreeDNA.
  2. Mitochondrial DNA tests offered by FamilyTreeDNA.
  3. Autosomal DNA test which is offered by all three companies but is the only test offered by and 23andMeFamilyTreeDNA’s autosomal DNA test is called the “Family Finder”.

Although 23andMe includes some analysis of the Y-chromosome and mitochondrial DNA as part of their product, this analysis only investigates the very deep ancestry of these DNA types.

The test results from each of the companies differ from one another in some aspects but have some basic shared elements. When your test results are ready, you will receive a notification to your email and you will be able to view them by logging into your account. Autosomal tests include ancestral ethnicity estimates as well as a list of genetic cousins or matches who are estimated relatives based on the amount of DNA that you share in common with them. Each company offers different tools for additional analysis of autosomal DNA test results.

Y-DNA and mitochondrial DNA tests also include some basic information about the geographic distribution of your DNA types, and also include a list of relatives based on the markers that you share in common. These test results also include a summary of the mutations on your own Y-chromosome or mitochondrial DNA that make them unique from other lineages. Sometimes deep ancestry information can offer clues, but it does not provide enough information to draw genealogical conclusions.

DNA Types


The Y-chromosome is only carried by males and is inherited in a line of direct paternal descent. A male receives his Y-chromosome from his father who inherited it from his father, and on and on. Occasional mutations help to distinguish different Y-chromosome lineages. Because surnames are often inherited in a similar pattern in many cultures, two individuals with the same surname and similar Y-chromosome signatures share a common direct line paternal ancestor. Likewise, two individuals with different surnames but who share the same Y-chromosome signature share a common direct line paternal ancestor. This situation may be indicative of a “non-paternal event (NPE),” which could include an undocumented adoption, illegitimacy, a surname change, or any number of other situations which might result in the paternal surname not being passed to both lines of descent.

Mitochondrial DNA

Mitochondrial DNA is carried by both males and females, but it is only passed on by females. Therefore, mitochondrial DNA is inherited along the direct maternal line. An individual receives their mitochondrial DNA from their mother who received it from her mother. Occasional mutations help to distinguish different mitochondrial DNA lineages. If two individuals share a mitochondrial DNA signature it may be indicative of shared maternal ancestry. Because mitochondrial DNA is much smaller than any other type of DNA, and because it undergoes fewer mutations over time, it is harder to make genealogical discoveries with this type of test. It is best used to offer support for genealogical hypotheses.

Autosomal DNA

Autosomal DNA tests analyze portions of the DNA that are inherited both paternally and maternally. Each person receives half of their autosomal DNA from their mother and half from their father. Autosomal DNA undergoes a process called recombination, which shuffles the maternally and paternally inherited copies of DNA before passing them on to the next generation. Each person receives exactly half of their autosomal DNA from each parent, but only approximate percentages can be applied to more distant generations of ancestors due to the random nature of recombination. Each individual shares about 25 percent of their DNA with each grandparent and half that amount for each subsequent generation. Individuals who share large identical segments of autosomal DNA most likely share a recent common ancestor.


The X-chromosome is one other type of DNA that has a unique inheritance pattern. Males have one X-chromosome from their mother. Females have two X-chromosomes: one from their mother and one from their father. The X-chromosome undergoes recombination in females, but not in males. Though the X-chromosome cannot be assigned to a specific line of descent, it can be used to eliminate individuals from a person’s tree as possible common ancestors to their matches. The X-chromosome is tested at each of the companies as part of their autosomal DNA tests.

Reasons to Test

Genetic genealogy tests can help confirm or refute genealogical hypotheses, open up new avenues of research, or they may not be helpful at all. However, as the databases grow and as more people test, the last result in this list is becoming increasingly uncommon.

DNA testing can be useful for answering questions regarding adoption, illegitimacy, unknown or misattributed parentage, name changes, immigration, and many other instances of difficult-to-trace ancestry.

While DNA tests have the ability to help investigation in these difficult situations, they also have the ability to reveal well-kept family secrets. Whenever a DNA test is taken, the subject should recognize the possibility of discovering previously unexpected relationships through undocumented adoptions and illegitimacies. Many times the discovery of these events can be surprising and may drastically change the way you view and approach your family history. Testing companies and private researchers do not claim responsibility for these discoveries and the impact that they may have on individuals and families.

Genetic Genealogy Success

Many adoptees have successfully identified their birth parents through genetic testing and other available resources. However, genetic testing can also be helpful for genealogical questions. Many have successfully used Y-DNA testing in conjunction with autosomal DNA and the historical record to identify fathers of illegitimate ancestors. Others have used autosomal testing to overcome recent genealogical brick walls. Yet others have used mitochondrial DNA to support descent from common maternal ancestors and to confirm or refute family legends regarding African or Native American ancestry.

In one recent case, we were able to reveal the identity of a client’s 2nd great grandfather through autosomal testing. A concealed illegitimacy had prevented previous contact with this part of the client’s family and as a result of DNA testing, we were able to extend the client’s ancestry several generations. Though we were able to answer the client’s research question, this research also opened new avenues of investigation since no member of the family has yet been able to determine the origin and parentage of their common 2nd great-grandfather who was born in the early 1850s in Missouri. DNA testing and collaboration with these newfound cousins may help to reveal this individual’s ancestry through future research.

Applications of DNA testing to genealogical investigation are many and varied, and they are also frequently successful. However, even when tests do not yield immediate results, as more people test and more matches are identified, genetic genealogy tests become sources that keep giving.

About Paul Woodbury

Paul Woodbury is a Senior Genealogist with Legacy Tree Genealogists, a genealogy research firm with extensive expertise in genetic genealogy and DNA analysis. To learn more about Legacy Tree services and its research team, visit the Legacy Tree website at