How to Read DNA Test Genealogy

by Patrick Gleeson, Ph. D., ; Updated March 15, 2018

DNA testing for ancestry has become a hot topic, fueled by celebrities' accounts of their test results. If you're interested in knowing more about your ancestry, a relatively inexpensive DNA test will tell you a lot. Be aware, however, that there's been some kickback on DNA testing; some scientists believe DNA testing firms are over-promising on results. Here's the 411 on what you can reasonably expect to find from your DNA test, along with an overview of the interpretation of the results these services provide.

What is a DNA Test

Actually, there are at least three different popular DNA testing procedures, one for establishing paternity, another for confirming cousin relationships and a third for establishing your ancestry.

The testing procedure is simple and quick. The DNA testing firm you choose will send you a kit consisting of a swab you'll use to gather your saliva, a vial to put it in and a return mailer. There's not much more to it than that, although your kit will include instructions on how to swab and cautions to take when mailing back your test swab.

Ancestry Testing

At birth, you and every other human being have 46 DNA molecules called chromosomes. These never change, and your specific DNA made up of these 46 chromosomes is unique. Scientists can establish different details of ancestry by comparing different aspects of your DNA with others, Briefly put, the more your DNA matches the DNA of others, the more likely it is you have common ancestors.

The details of DNA testing can quickly run into the weeds, but the simplest way of looking at it is that a DNA test for ancestry compares your DNA makeup with the DNA makeup of others using one or more of three tests:

  • Mitochondrial DNA testing, which establishes your ancestral links using mitochondrial DNA that you inherit from your mother 
  • Y-Chromosome testing, which establishes ancestral links using Y-chromosomes that you inherit from your father
  • Single nucleotide polymorphism (SNP) testing, which compares different SNP markers across all 46 chromosomes

Interpreting Your Results

Interpreting the results of all three of these DNA tests requires considerable expertise. Fortunately, your DNA testing service interprets the results for you. Mitochrondrial DNA tests confirm or disallow specific ancestral links on your mother's side. Y-Chromosome tests do the same thing for links on your father's side. SNP test results establish the likelihood of your links to ancestral groups, along with an assessment of the percentage of each ancestral components. Model and entrepreneur Tyra Banks, for instance, took such a test and determined that her ancestral makeup is 79 percent African, 14 percent British and 6 percent Native American. Similarly, your test results will include the percentages of each component of your own ancestral makeup.

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About the Author

I am a retired Registered Investment Advisor with 12 years experience as head of an investment management firm. I also have a Ph.D. in English and have written more than 4,000 articles for regional and national publications.