One of our genealogists shares her answer to the question, “Why don’t I share any DNA with my known relative?” after her own surprising DNA results.
Recently, Carolyn Tolman, Project Manager at Legacy Tree Genealogists, and I discovered we are fourth cousins. Her great-great-grandmother Rosa Clark is the sister of my great-great-grandmother Sarah Annie Clark.
Carolyn and Candace, fourth cousins.
Not long after we made the discovery, we were sitting in a DNA chromosome mapping session together at Roots Tech. I leaned over to her and suggested we use our shared DNA to begin mapping our Clark DNA. We logged into our AncestryDNA accounts immediately but couldn’t find each other in our match lists! What if one of us had misattributed paternity? What if one of us is not biologically a Clark?!
Maybe we had just missed each other while quickly scanning our DNA match lists. Thousands of matches aren’t easy to skim through, especially while listening to a lecture. We moved to GEDmatch where we could quickly compare our kits in a one-to-one autosomal DNA comparison. (Autosomal DNA includes all your chromosomes except your sex, X and Y, chromosomes.) The results were definitive. We share no DNA—zero centimorgans.
Why Don’t I Share DNA With My Known Relative?
What do you do when you know you should be related to someone but you share no DNA? Is the analysis tool wrong? Do one of you have a big family secret waiting to be discovered? It’s not the tool, and regarding a big family secret—maybe yes, maybe no. It depends.
Because we get to analyze DNA results every day at Legacy Tree Genealogists, we knew that fourth cousins don’t always share DNA. According to a study cited by ISOGG, there is a 30 percent probability fourth cousins won’t share autosomal DNA.[1] There was no need to panic yet.
We decided to compare our DNA a generation closer. We compared her father to me—third cousins once removed—and still no shared DNA. I knew my aunt had tested and uploaded to GEDmatch so I located her kit number and we compared my aunt to her father. Almost 98 percent of third cousins share DNA. If they shared no DNA, then it would be time to consider the possibility of misattributed parentage on one of our lines. With relief, we discovered her father shares 28.7 cM of DNA with my aunt.
The Role of Genetic Inheritance
You might ask why I share no DNA with Carolyn’s father when my aunt does? My aunt’s DNA contained segments that either my mom did not inherit or that my mom did not pass on to me. This is why it is so important to test multiple relatives and examine each of their DNA match lists when solving a DNA mystery.
You might also notice that Carolyn’s dad and my aunt share a low amount of DNA for their proposed relationship. In fact, this amount of DNA has only an 8.87 percent probability for third cousins. Does this mean there is a different relationship, not third cousins on the Clark line, that is the real relationship? Is there STILL a big family secret? We scanned our match lists for a key match—a descendant of Annie and Rosa’s siblings—someone we would both match but is independent, not descending from either Annie or Rosa. Such a match could help in confirming that neither of us have a break in our biological line. Sure enough, we found a match descended from a brother of Sarah Annie and Rosa who was on both our match lists sharing a reasonable amount of DNA with both of us. We could search further finding additional matches who descend from other siblings.
Because of the document evidence showing our relationship and the DNA evidence between Carolyn’s father and my aunt, and our shared Clark matches, we can reasonable conclude there are no family secrets in our Clark line and we really are fourth cousins, by blood, even if we share no DNA.
If you’ve taken a DNA test and need help analyzing the results, or if you have a genealogy question you think DNA might be able to help answer, we would love to help! Contact us to discuss your questions and goals, and we’ll help you choose a project option and get started.
[1] ISOGG Wiki, “Cousin Statistics,” International Society of Genetic Genealogy, https://isogg.org/wiki/Cousin_statistics, accessed April 2019.
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Thank you for explaining this. My mother(deceased) never knew her father but he was listed on her 1929 birth certificate. I have researched his life but in uploading my dna. Absolutely no matches from his lineage nor anything explaining that I have more Greek -10% than Irish 3.4%. I would love to know if there is family on that side and get meds hx. What are the chances he truly was her father but has no living relatives to smart match with my DNA? Thank you !
DNA can certainly help in confirming or refuting your maternal grandfather as the man listed on your mother’s birth record. Ethnicity results can be variable depending on which company you test at. Without knowing details, we generally recommend relying more on the cousin matching available at the testing databases, and adding any clues the ethnicity results can yield together with the cousin match lists.
Consider testing or uploading to each of the major autosomal DNA testing companies and also enlisting other known relatives to do the same. If your mother did not have any full siblings, you can use the DNA of your father, a paternal aunt or paternal uncle (or paternal first cousin) to help remove your paternal matches from consideration, as well a maternal half aunt/uncle (or maternal half first cousin) if your mother had any half siblings. Remaining matches who do not share DNA (are not shared matches with) with your known relatives could be related through her paternal father. If he was a recent immigrant from a country with a low test rate, it is very possible there are few matches related to him on your match list. It is essential in situations like these to be in each of the major databases to have access to unique users. It is also possible matches related to him are buried in your other matches or share secondary relationships to your other matches, making them more difficult to identify. This can be sorted out. Once clusters of unknown matches are identified who may be related to him, you will want to identify their common ancestors and determine how you might fit into that that ancestral line. You may want to begin with identifying her presumed biological father’s descendants and inviting them to test.
We can help with these steps—identifying his known descendants and providing contact information to invite them to test, selecting the best known relatives to test and examining your cousin match lists, identifying their common ancestors and determining how you might fit into the ancestral lines, and then identifying potential birth father’s for your mother. We are passionate about finding birth parents through DNA and would love to learn help you learn more about your ancestry. To request a free quote, please complete this form.
23 and Me sent me names that we share 100 cm and related but the ones like Maureen Shaw says the names do not match and we are not related but names get changed.
Wow. Does it apply to 2nd cuz?
The ISOGG cited cousin statistics show there is a 0% probability of no detectable DNA between second cousins, meaning that if you and your known second cousin do not share any DNA, then there is likely misattributed parentage somewhere along the line OR the relationship is more distant than believed (a grandchild unknowingly raised as a child by grandparents, half relationships, etc.). If a presumed second cousin relationship were really a half second cousin once removed, this would be equal to a third cousins, which again, are expected to almost always share DNA but statistically do not always share detectable DNA (the statistics show only 2.3% of third cousins would not share a level of detectable DNA). Comparing DNA in a one-to-one comparison at GEDmatch and also examining shared matches for each level of ancestry can help solve whether there is misattributed paternity or whether the relationship simply is more distant than originally thought.
I do not share DNA with a known fourth cousin of mine. She also does not share DNA with my first cousin or my second cousin that she is documented as being related to. I found another distant cousin we are both related to and, looking at in-common matches that we each share, we are now confident that we just happened to not inherit the same DNA. Given the black-sheep nature of this family, it wouldn’t have been shocking to determine that a mother had a child that was not fathered by her husband. Thankfully though, we’re reasonably confident that is not the case.