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.
I have a known 2nd cousin 1 removed that our DNA does not match. We know that we’re related because we have several common matches (relatives that match both of us but we don’t match each other.
I have a question. I found a DNA relative. 4-6 cousin. Now her daughter doesn’t come up as a match for me. However her granddaughter through her daughter does. How could that be?
Hi, I have a question if someone would be so kind to answer? My sons match someone with about 267 cM’s of dna. the person with whom they match is not a match for me, so I assumed that he matches my sons on their father’s side. At between 170 and 267 cM’s can I assume that he would be a child of my husband’s 1st cousin? OR is it all possible that he could be related to my sons through me, but at the same time not share dna with me?
Thank you for any help in answering these questions.
Hi Jane, thanks for your question. You are correct–the match is most likely a match through your son’s father’s side. Based on genetic algorithms, the match could be several relationships: (see below, from DNA Painter)
– 60.76% Half GG-Aunt / Uncle 2C Half 1C1R 1C2R Half GG-Niece / Nephew
– 21.48% 1C3R † Half 2C 2C1R Half 1C2R
– 17.76% Great-Great-Aunt / Uncle Half Great-Aunt / Uncle Half 1C 1C1R Half Great-Niece / Nephew Great-Great-Niece / Nephew
It all depends on how someone falls in their family tree as opposed to how their match falls. We recommend checking out dnapainter.com. Good luck!
My friend and I took Ancestry.com DNA tests. Just for fun, we thought we’d compare test to see if we were related, but we share no DNA. However, I started to notice that we did share many of the same relatives (more than 100.) Is it possible that were are cousins, though, we share no DNA, or is it we just have many of the same relatives in common?
Thanks for your help.
With Three autosomal DNA tests My paternal uncle, my brother, n myself.. My uncle doesn’t match us.. Did Y dna got more confused cause matches have two different surnames n one same.. But how could the younger son match the father the older son came from yet not match us?? I know that the father had cancer of the prostate n died.. I thought there were two different dads but one guy in ydna is telling me no I’m wrong to go off of autosomal.. Who’s right??
Good morning. It sounds like there are quite a few details to this scenario–more than could be easily dissected in a single comment. May I suggest schededuling a Genealogist-on-Demand™ Virtual DNA Consultation? This will provide you with the opportunity to chat with one of our genetic genealogists, one-on-one, for 45-minutes in a virtual screen sharing platform. To schedule, visit: https://legacytree.com/dna-consultation.
Hi I suspect I may not be my fathers daughter , can I do a dna with a first cousin and would it show we were not related if indeed this was the case, would cousins results be definite thanks. Confused .
Hi Helen. Yes, a DNA test can be performed with a known paternal first cousin as a first step. If no DNA is shared between you and your cousin, and if your cousin shows matches in his or her match list who belong to your presumed paternal line, but you do not share those matches, that is an indication that your paternal line might not be what you previously believed. However, this is not a guarantee that your father was not your father. Consider also that your father could have been adopted. If you have a sibling who can test to determine if you are half or full siblings and can also examine their shared matches along their paternal line, a stronger conclusion can be reached. If you have additional questions, you may consider scheduling a Genealogist-on-Demand Virtual Consultation with one of our genetic genealogists. They can walk you through your test results and help you put the pieces together. You can schedule a consult here.
It was stated that 98% of third cousins share DNA… I think the most extreme case – with an extremely low chance of happening (but then there are billions of people on the planet) – is this ..
Sibling A receives paternal paternal C1, C2, C3 … and maternal paternal C1, C2 etc…
Sibling B received paternal maternal C1, C2, C3 .. and maternal maternal C1, C2 etc…
Sibling A is female, Sibling B is male… then they share zero DNA with each other.
The likelihood of this ever happening — because of homologous recombination events (where chromosomes break and crossover between the maternal and paternal in the sperm or egg) .. is really really low.
But this extreme case highlights why it is quite easy for shared DNA to get lost from generation to generation. Another thought experiment is that if you go back 20 generations, you have about 1 million great grandparents in that generation. We all have 2 copies of only 20,000 genes. A lot of those genes travel together in the large segments we do inherit… so we can only inherit our complete DNA from probably much less than 20,000 of those million ancestors 20 generations ago.
Thanks for sharing your thoughts, Oliver!
My two siblings match me as full siblings…we all match with second cousins on our fathers side, sharing the same great grand father…my great grandfather had a first wife and therefore a half second cousin took a DNA test. My two siblings and two second cousins match her nicely but I did not match her at all. What are the chances of this happening? I feel a little left out. Thank you in advance
A half second cousin, according to ISOGG Wiki’s Cousin Statistics, has only a 0.10 percent probability of no detectable DNA. If this match is a generation younger than you and your siblings, that probability would jump to a 2.30 percent probability. Although it is unusual, it does happen. It may depend on how and where you are looking for shared DNA. If you are at AncestryDNA and are looking to find him or her through shared matches, remember that only shared matches sharing more than 20 cM are listed as a shared match. Also, some testing companies are quite conservative in measuring shared DNA. For instance, AncestryDNA removes segments deemed common in the community using their proprietary Timber algorithm. To be sure you fall in the very low probability of sharing no detectable DNA, you may want to make a direct comparison of your DNA and your half second cousin’s DNA at GEDmatch with their one-to-one comparison tool or another database you can both upload to for a second opinion. If that still shows there is no detectable DNA shared between you, remember that someone has to be in the low probability ranges for the low probabilities to exist. You might just be the lucky one!
There are 22 autosomal chromosomes that are likely to give you the connection to those half 2nd cousins.
You inherit either your father’s mother’s copy of any of the 22 chromosomes… or your father’s father’s copy. Or a combination of the two.
You could inherit chromosomes from your paternal grandfather that match your 2nd cousins. And rather than the chromosomes that match your half 2nd cousin, you could have inherited your paternal grandmother’s copies of them…. whereas your siblings could have inherited those that link to the half second cousins.
I agree with uploading all the results to GEDmatch and then run a comparison in their 3D chromosome browser. That will give you a summary of all the matches between you all.
I have done my DNA and family tree, I have had several matches that the results say 1rst and 2nd cousins. My question is we have no common ancestors in any of our trees even though some of my other matches share a common ancestor. My question is this. There was always question on my grandmothers father if he was really her true dad. My dna hits several people in my family but of course we all share the same grand parents. How do I figure out why these dna matches match me? Plus I had contact from one of the ladies wondering the same thing on how we could be 1rst or 2ns cousins.
Thank you
I find myself answering this…. because I had a similar situation – for 70 yrs we did not know who my grandmother’s father was. For me this means that my family tree on her father’s side was empty.
Eventually I found a common ancestral surname among a number of DNA matches who I could not place and I mapped out the ancestral lines of those DNA matches. Eventually they began to criss-cross to a single surname. Then I worked out marriages in the decades before my grandmother was born… and tracked them down. Eventually I discovered that I had DNA matches on two side of a single couple. They had to be the parents of the father of my grandmother. it was a lot of work. Now I have lots of 2nd cousins.. but I’ve not made contact with any yet. How do you tell them their grandfather / great grandfather had a child before he married their grandmother/great grandmother. And he didn’t know….
So… it is really only possible to do this if you have done a DNA test.. and I have done both 23andMe and Ancestry… but it’s not easy.
Thank you, Oliver! Great suggestions. We’re glad your efforts paid off and you were able to make progress on your paternal side!
Whenever close unknown matches exist with no common ancestry, several steps need to be taken to determine whether the misattributed ancestor is on their line or your line.
Carefully sort your matches into clusters of shared matches representing each of your ancestral lines. For this situation, see if you have clusters of shared matches at estimated second- to third-cousin levels (or more distant) representing at least each of your great-grandparent lines and, if possible, your great-great-grandparent lines. If your grandmother’s assumed father’s lines are not represented among your matches, it is possible the family story about your grandmother’s father is true.
Identify which of your known matches these new unknown matches share DNA with. This will help you determine how they may be related.
Collaborate with the unknown first- to second-cousin matches to do the same for their great-grandparent and second-great-grandparent lines. If their ancestry is proven through their more distant matches, it may be your line that is misattributed.
Identifying all the possible relationships to these unknown matches, identifying additional clusters of matches, and performing targeted testing may be necessary to narrow down your connection, along with document research. This can be a complicated process but DNA has the ability to solve these mysteries. We are happy to help you on your journey. If you would like research assistance, you can get started by requesting a free quote here.
Hi – thanks in advance for any help you can give.
I am helping a female friend who is an adoptee build her family tree. She has taken an Ancestry.com DNA test. That test revealed two 2nd/3rd cousin matches. We reached out and found that they are full brother and sister. Because they are both a match, does that mean that we only need to research their mother’s side of the family? My logic is that the only way they could both match is on the X chromosome they inherited from their mother?
Hi I am trying to find my great great grand father, no one has ever made a tree or done dna until now. My family is pacific Islander but my great great grand father was a white man but no one knows who he is we only have ever had a name to go by that may or may not be correct. My dna results came back and as we expected it shows mostly Pacific Islander but 6% various European countries. I have 2500 very small % matches and can not find links anywhere but had a good lead and this guy was in the right place the right time and his face is a great match to many members of my family…… BUT I only have found this one dna match and it is very small , the guy is in their tree but it takes many twists and turns ( daughters name changes ect. ) but there is a line there. Can this be the guy even though I have no other links like hits on other direct members of his family? If it is him should I not be seeing many other matches to him ? I’m confused.
Hi Rachel, without being able to review your results, it’s difficult to draw a conclusion. I would suggest scheduling one of our Genealogist-on-Demand Virtual DNA Consultations so that a genetic genealogist can review the results with you one-on-one and discuss the different possibilities. You may schedule at https://legacytree.com/consultation. Good luck! We look forward to helping you find answers.
My second cousin and I took dna test with ancestry. We are not a match. Our mothers were first cousins ( both are deceased) My grandfather and her grandmother are brother and sister. Her grandmother, however, married her first cousin. Could this throw a wrench into the mix ? my cousin matches to one of my first cousins as a second cousin. Any cousins that have dna from her grandfathers side, are not match to me, but should be because he would be my grandfathers first cousin too!. What;s up with this ?