A big thanks to professional genealogist Melissa Johnson for unraveling some of the mysteries surrounding genetic genealogy. Using genetics as a tool for genealogical research is an ever-expanding field and Melissa did a wonderful job of explaining the many facets of the field for amateur and professional genealogists alike. One of the most common questions is determining which DNA test will yield the best information and as with many answers, the simple answer is “it depends”. Let’s cover the 3 types of DNA testing:
- Y-Chromosome Testing
- Tests the Y-chromosome that is only passed down through the male line
- Mutations can occur which can help identify how closely related 2 Y-chromosome DNA matches are likely to be
- Only shows that there is a male relation, but will not pinpoint which male it is (ex. brothers)
- SNP Test (single nucleotide polymorphism)
- designed to help identify deep ancestry and haplogroup
- STR Test (short tandem repeat)
- examines a specific number of markers (11, 37, 67, or 111)
- Testing 37 or more markers is best for genealogical research
- Family Tree DNA’s test shows non-matching STR markers, known as the “genetic distance”
- Genetic distance of 2 or more may indicate common ancestor for 2 people is much farther back, outside of a genealogical time frame
- Designed to answer a specific question, such as “Are Person A and Person B brothers”, rather than “fishing” for potential DNA matches
- Mitochondrial Testing
- We all have DNA from the mother’s side and this test looks at that DNA; however, this DNA can only be passed on by female children
- As with the Y-chromosome testing, results will only show a female relation, but will not pinpoint which female it is (ex. sisters)
- mt Full Sequence test is best for genealogy, while mtDNA Plus only tests 2 regions and is best for determining a haplogroup
- Designed to answer a specific questions, such as “Are Person A and Person B sisters”, rather than “fishing” for potential DNA matches
- Autosomal Testing
- Most common type of test that looks at 22 of 23 chromosome pairs (excluding gender)
- Shows patterns in our DNA that we have inherited from our ancestors, usually within the past 6 generations
- A 50/50 split of DNA from mother and father rarely occurs
- The test measures the amount of centimorgans that we have in common with other people, which will roughly determine their potential relation to us
- A useful chart can be found at https://thegeneticgenealogist.com/2017/08/26/august-2017-update-to-the-shared-cm-project/.
- This type of test is best if we are just trying to “fish” to see who we might be related to
With many DNA tests come a breakdown of our ethnicity. These breakdowns will vary for each testing company, based on the sample DNA from populations determined to be native to different areas of the world. These tests have little impact on actual genealogy and should not be used to focus your genealogical research or serve as the main answer to any genealogical question.
Genetic testing, even for genealogy purposes, poses some ethical questions to consider. Some tests will also look for potential health-related risks that may make some people uneasy. Additionally, testing other’s DNA may lead to hidden truths about their parents or ancestry that might pose a challenge, such as learning a parent had an affair. Determining what people are willing to test for and what they want to know is important to consider when venturing into genetic testing. Additionally, if you are going to be uploading results or posting information based off of someone else’s DNA results, please get their consent to do so.
If you have questions about DNA tests, genetic genealogy, or general genealogy, please contact Melissa Johnson at firstname.lastname@example.org. You can download a copy of the handout at Diving Deeper into Genetic Genealogy Handout. Also, please visit our Genealogy Research Guide for many helpful tips and resources!