It’s not unusual for a customer to tell us there are two possible fathers for a child and that those two fathers are biologically related. Although two possible fathers who are related don’t share all their DNA (unless they’re identical twins), they do share enough that getting conclusive results for paternity testing may be problematic. So can paternity-test results under these conditions be trusted? Yes! Here are some relationship possibilities and how they may affect test results.
If Possible Fathers are Brothers
It’s important to remember that, although they are closely related, full brothers each have very DNA profiles that are still quite distinct from each other. The chances of two brothers who are not identical twins matching a child at each genetic marker for paternity testing are not likely. But since the relationship between possible fathers is so close, we still recommend that each of the men test with the child, if possible. At the very least, it’s essential to notify the lab that there are two possible fathers and that they are brothers. The lab can then test more genetic markers, if necessary. It’s also important to include the child’s mother’s DNA in testing. When you include the mother’s DNA, it helps analysts to more easily determine which data is coming from the possible father and which is coming from her.
If Possible Fathers are Twins
Fraternal Twins
If the men are fraternal twins, the DNA connection between them is the same as it would be for “regular” brothers. As when “regular” brothers test, it’s best when both men can test and the mother should also contribute a DNA sample to strengthen paternity testing results (see If Possible Fathers are Brothers, above).
Identical Twins
For identical twins, their DNA is as you would expect: exactly the same! With today’s level of technology, this makes being able to genetically differentiate between the twins for paternity testing purposes practically impossible and completely cost-prohibitive since it would require testing most of their genetic markers instead of the standard 16.
If Possible Fathers are Father/Son
A full 50% of the son’s DNA comes from his father, so if these two men are the possible fathers for a child, there is a high possibility of obtaining a “false positive” result if only one of the men participates in testing. Therefore, the ideal is for both men to test with the child. If this isn’t possible for whatever reason, then the lab must be notified ahead of time (so that additional analysis can be conducted) and the mother should definitely send in her DNA sample as well.
If Possible Fathers are Cousins
Even men who are first cousins don’t share enough genetic material in common to cause a “false positive” for a paternity test: the connection is just too far removed to make a significant difference.
Final Thought
To repeat the most important points: In all cases where two possible fathers are closely related, it’s best if both men can test at the same time. If there is a close genetic connection between possible fathers, and only one man can or is willing to test, it’s important to notify the lab about the biological relationship when submitting DNA samples: better safe than sorry!
I am not sure if the father or son is my child’s father. Will the paternity test be clear if only the father is willing to be tested and the son is actually the father?
Hi, Anna. Excellent question! This is very important: If only one of them can or is willing to test, you MUST let the lab know ahead of time that there is another possible father and what their biological relationship is. That way, the lab can take this into account in their analysis and test more genetic markers, if necessary, to obtain conclusive results. It’s also helpful for you to contribute your DNA to the test as well.
What will the DNA results show if I decide to just wait and get results with father being tested for paternity as the son has refused? Will the test results be negative or inconclusive if he is not the father?
I have a suspicion that the son is actually my child’s father but I can proceed further if the results are not conclusive.
Ann, with today’s technology and methods, an accredited lab should never return an inconclusive result for a paternity test. When the father tests, it’s absolutely essential that you let the lab now ahead of time that the other alleged father is the son of the man being tested. That way, the scientists can take that info into account when doing their analysis. They can test additional markers, for example.
I’m curious ann as to what the results showed, I’m in the same situation and could use some answers.
I have a question which I have gotten some conflicting answers on. The question I have is if my fathers brother (my uncle) is the other possible father of my child, is that a close enough relative to me to produce a false positive for me on the paternity test ? I already tested and got back the result of 99.99% with a CPI of 19,091. I am wanting to know if we are close enough relatives for it to affect the results of my test ? I would really appreciate your help on sorting this out. Thank you.
What blood types aren’t compatible without having the rh- shot?
Hi, I have a couple of questions I thought hopefully you might be able to answer…1st if a DNA test came back only 97% probability, would that mean I’m the Father? And second my kids Mom & my mom are sisters, my mom had here tubes tied before I would have been born. But just by some miraculous chance my mom did conceive me after that, which would obviously make my kids mother myself maternal cousins, what kind of result would you get?
Hi, Steven. I want to make sure I understand this correctly. Your kids’ mom is your maternal aunt?
Hi, I did a paternity test on my two
Kids, 2 and 8. I let the lab know ahead of time that the possible father might be my father or the kids grandad. He tested as well and was ruled out. The lab did extended testing and I matched at every marker except for one. The lab tested 30 markers. The one marker i didn’t match at shows a one step mutation, and CPI is .0003 for that marker. Is it possible one of my brothers may actually be the father?
Hi. If you want to rule out the brother completely, then he would need to do the test as well.
I am interested in clearing up the relationship between myself and sibling. I have a suspicion that my father and my siblings father were brothers (same mother) We are older and parents all deceased. Can this be definitively shown?
Thank You
Hi, Bob. Did either of you know your fathers?
Like Bob (Nov. 15 2018 above) my brother and I share the same mother. She is still living. The three of us have been DNA tested: mom and I via 23andme, and my brother by MyHeritage. We’re confused in that my brother and I only share (as per MyHeritage) 38.4% DNA. I thought we would share closer to 50%. Since our shared DNA percentage is much lower, could this mean we might have separate fathers, who were perhaps brothers? Or is this 38.4% in the realm of same parents?
Hi, Steve. I talked to our Chief Science Officer personally about your question. He thinks that 38.4% if a little low, but it’s not out of the realm of possibility for two full brothers. It really just depends on what you inherited from both parents in the genetic lottery. It is possible that you had fathers who were brothers…have you asked your mother about this? If it is possible that the fathers were brothers, then doing a Y-STR test with you and your brother wouldn’t do any good, since the two fathers would also share the same Y chromosome. You could do a sibling vs. half-sibling DNA test (with your mother including her DNA) while notifying the lab ahead of time that there may be another alleged father who is the brother of your presumed father.
Thank you! Great information and so quickly. Will connect with my brother and maybe mother as well, however this could be a touchy topic. She would probably be up for another DNA test and I could just leave it at that. My brother and I are quite interested in finding out more. Again – thank you!
Yes it might be a touchy topic, for sure. You’re welcome, and good luck. If you have any other questions, feel free to reach out again.
I had sex with two different men at the same day who could be the father now?note:they are not related at all,
Hi, Deborah. Only a DNA test would be able to give you that answer.
Hi, what if the two potential fathers are half brothers ( they share the same mother but different dads), is it possible to accurately determine the father of the child if you only have samples from one of the half brothers?
Hi, John. The answer is yes. However, two things are very important:
(1) The mother of the child should be tested also
(2) The lab must be notified ahead of time that another alleged father is the half-brother of the man being tested. This way, they can take this fact into account when doing their analysis.
Hope this helps!
Hi, how will i know if its my husband child can they used his brother sample as her kid and my husband sample to make a positive result? My husband is forcing to be the father but we don’t see any similarities of him and the child and the girl confessed that they were five men at same time when they mess up together.
Hi, Jenny. Substituting the uncle’s DNA for the possible father’s is not likely to yield a positive result. To be safe, it would be wise to insist on a legal paternity test where DNA collection is witnessed and IDs are checked. I suggest you contact us directly to speak with an expert at 800-681-7162 (M-F, 8 am to 8 pm Eastern).
Hi, on the test does the allele on the y side represent allele on the y gene. Did a test for me and my son and some of the numbers on the right side where the Y is on the paper dont match. Came back 99.999.
Thanks
Hi, Wayne. There is no “x” and “y” side on the data for paternity testing. Each allele shows the two sets of data in no particular order. For example, if data shows 12,11 then the 12 could come from either the mother or the possible father. Please contact the lab where you tested if you want additional clarification.
Hi, Both fathers in question are dead but my sisters father is the brother of the man I think is my dad. He is also dead.. Can I do a DNA TEST with my sister to see if our fathers are related.. We both have the same Mother.
Hi, Dani. Because you and your sister share the same mother, you already know you are half siblings and a test is not necessary to determine that. You may want to test with someone whom you are certain is related to your possible father in the first degree: like a known child of his. I suggest you give our experts a call so you can walk through your situation with them on a one-on-one basis and see what your options are: 800-681-7162.
hi….what if two guys are involved and they are related but only one does the test and the percentage came back as 97% is he the biological father
Hi, Marlene. If the lab was not notified ahead of time that the other possible father is a close relation (brother/father/child) of the man being tested, than that information was not able to be taken into account during analysis and any inclusion result cannot be relied upon to be accurate.
Hey so yes this a mistake I sleep with 2 cousin but my son look like the man who I think it is my son have similar features to
His daughter but I’m
Confuse bc they cousin is it possible he the other dude bc he look just like the little girl and the man with the lil girl agree on a dna test but the other dude don’t wanna do
It
Hi, Emily. You can get accurate results for a paternity test. Just be sure to let the lab know ahead of time about the biological relationship between the man being tested and the untested possible father so that they can test additional genetic markers, if necessary. If you submit your DNA for testing, that is definitely helpful to conclusiveness too. We can schedule that test for you and make all arrangements. Just contact us at 800-929-0847 (M-F, 8 AM to 8 PM Eastern).
Hello! I have a unique to situation. I have used your site for dna however. Have now found out more information. It is an incest case. Originally we tested my bio dad myself and the child out of invest. We were told it was my dad and his sister at a young age then had a child. We tested incest child,and my dad. However the test was not 99.9 I didn’t know we could go further as now thier is speculation that it was may have been my dad & his sisters actual father. My grandpa! Not my dad at all? My dad has since passed since first test and unfortunately my dad’s family will not allow a swab of “grandpa” . Is thier anyway to retest my “half sister(thru incest) and myself with proper testing to see if we really do have same father now knowing more information?
Hi, Erin. You’ll need to call us directly to see what your best options are in light of this new information: 800-681-7162 (M-F, 8 AM to 8 PM Eastern).
Hi, a female slept with identical twins at the time of her conception. The baby is about 2 years old now. Is there any way for the mother to establish which twin is the dad
Hi, Sara. No, there is not, unfortunately.
I had a dna test done and I was turned out to be 99.8 Percent the father , but she had relationship with my brother and he wasn’t tested do we need to do another to see if I’m the actual father or if he is .. we are full siblings .
Hi, Earnest. Unless the lab was told ahead of time that the other possible father is your brother, then yes…another test would be advisable. This time, it’s important to either have your brother test too or at least let the lab know of the relationship so that they can take this info into account when performing their calculations. If the mother is willing to test too, that’s optimal. Good luck! If you are interested in testing through DDC, contact us for a free consultation at 800-929-0847 (M-F 8 AM to 8 PM Eastern).
Me and my dad got a DNA test but there is a possibility that his brother might b my dad. The test come back saying he isn’t my dad but is there anyway we can determine if we are at least related in someway from the test result
Hi, Anne-marie. The best way to answer that question definitively is to test the uncle, if possible.
My son and alleged father had a DNA testing done. Results came back he cannot be excluded as the biological father and it was 99.9987%. The alleged father believes he still is not the father since the other person did not test. There is no relation other than same ethnicity. Is another testing needed?
Hi, Marie. Unless the two men share a close biological relationship, then no, there’s no need for additional testing. 99.9987% is an extremely conclusive result.
Hello. My half brother passed away before getting Dna done for his daughter. His legal wife (since next of kin) refuses to give release for his Dna. Here’s where it gets complicated. Him and I share the same mother and our fathers are actually brothers. Can I give my blood for the DNA test??
Hi, Jenn. You’re right that it’s complicated. You are trying to find out if the daughter is your biological half-niece. Is that correct? Since your fathers were brothers and there are variables in play that would make a back-and-forth written discussion in this forum difficult, I suggest you contact one of our DNA experts directly to see what your best options are: 800-929-0847 (M-F, 8 AM to 8 PM Eastern).
Yes you are correct. So technically his dad was my uncle and my dad was his.. My mother married brothers.
Two men get tested to determine the paternity of their daughter (they both think they are the father).
After the tests, one of them is the father. Neither one of the men suspects they are related to each other. Let’s presume they are.
Would the DNA test done to determine paternity inadvertently discover the relationship?
Hi, Julia. That’s an excellent question! It depends on how much DNA the two men share in common, whether they’re brothers or father/son, etc. What I’ve definitely seen a few times is this: a man is excluded as the father (meaning he’s not considered the biological father), but the lab made a notation in the report of the possibility that the actual biological father is related to the man who was tested.
I’m 51 now and finding out that my fathers brother in law may actually be my father. Both are deceased, would I check both my aunt (fathers sister) & her son or how would that work? If I don’t have dna matching my aunt but I match her son does that mean that my uncle(fathers bro in law) is my actual father?
Hi, Laurie. You most likely would do an avuncular (aunt/uncle) test. Since your situation is complicated, I suggest you contact us directly for a free confidential consultation to determine what type of testing might be best: 800-681-7162 (M-F, 8 AM to 8 PM Eastern).
My full sister had an affair with my ex husband, and during that time she had a baby, my niece. She lost custody of my niece due to drugs, and I have the baby in my custody now. Neither one of the adults are willing to participate in a DNA test to determine paternity. Can I have my niece tested against my children to determine paternity?
Hi, Rebecca. Yes, you can do a sibling vs. half-sibling test to help determine the relationship between the niece and your own kids, as long as you have legal guardianship. I suggest you contact us at 800-681-7162 (M-F, 8 AM to 8 PM) for a free consultation with one of our experts.
I have a question I had relationship with a father and son not knowing anything of the situation of them being related but I had the jr test my courts and I advised the courts of the situation! The son came back 99.99 percent the father is the test accurate? I was told maybe not because a father and son share dna but the courts knew before testing about father and son in question
Hi, Stephany. Since the court was notified, they should have also advised the laboratory and the lab would have taken this information into account when performing their analysis.
What if the aunt passes away before she agrees to a test?
My daughter had a dna test done and the results came back 99.96 but the other alleged father who is the other mans brother was not tested nor mentioned to the testing agency is there any possible way that the results could be wrong and his brother is in fact the child father?
Hi, Sami. In cases like this, a false positive may occur. It really depends on how much DNA the brothers happen to have in common at the locations tested. It’s essential that your daughter be tested again, hopefully this time with both men. If that’s not possible, then the lab definitely needs to be made aware of the other alleged father and his biological relationship to the man being tested BEFORE they do the testing.
I have a son who is almost 30 there is a possibility between 2 men, not related one is deceased the other is alive & well. Which is the best way to get a DNA test on the man that’s still here. Only thing is he lives in a different state?? Help please? Can it be done by mail?
Hi, Ruth Ann. The possible father living in a different state is no problem. We would just send testing materials to you and your son at your address and then send a kit to the man at his address. Just give us a call at 800-681-7162 during business hours.
Hi I need your help, iv tested my Y dna with a Y dna genetic tester and tested the Y dna of the man I think is my farther, out of 132 genetics I shear 99.96% including 5 countries, I tested The YSNP numbers .cheers.
Hi, Dave. Your report should have provided a conclusion for you. If not, please contact the lab where you tested.
Need DNA Test
Hi, RZ. Call us! 800-929-0847 (M-F, 8 AM to 8 PM Eastern).
If two are married and wife cheats and get pregnant can the real father ask for a dna but no prof he is the father
Hi, Kristi. If a child is conceived and born during a marriage, the husband is considered the legal father of the child. Whether or not the other man can request a paternity test is up to the individual state where you live since paternity law can vary.
Hi I slept with two brothers days apart .. If I get a noninvasive prenatal dna test will they be able to determine which brother is the father? I would only have access to one brother for the test. The other one is not gonna provide a sample.
Hi, Tessa. No; because of the way the data is analyzed, a prenatal paternity test cannot be performed reliably if possible fathers are closely-related (brothers, or father/son).
Good day is it possible to have identical half sibling match and a negative aunt test
Hi, Tc. Can you give more specific information, please?
I did dna test brother 37.2 dna shared 2600cm longest 191cm shared 43 sagmates full brother or not .
And I’m xy female and we don’t share x or y
Hi, Shannon. Without all the data in front of me, I hesitate to answer your questions. Since they have access to your report, I suggest you contact the lab where you tested directly and ask them.
My son did a DNA test on who he thought was his son. It turns out there was 0% probability of him being the father. If the real father was actually my son’s father would it show on my son’s test
Hi, Shannon. Are you suggesting the grandfather might actually be the father of the child in question?
Hi there my brother did a paternity test and it came back 87% but the statement read this ‘ the possibly exists that a direct relative of the alleged father could not be excluded as the biological father’ do you have any thought to was that is implying?
Hi, Lucy. I’m surprised that your brother was given a result of 87%. Most accredited laboratories will only provide results of 99.9% or higher for an inclusion or 0% for an exclusion (not the father). What the report is stating is that your brother most likely is not the father but there is a chance that the biological father could be a different brother or your father.
My brother died and he two daughters behind, their mother disappeared, those children doesn’t have Identity documents and they’re schooling and growing up. What must i do to help them ?
Hello, Phillip. Please contact a local family-law attorney since that would be your best resource for what is required for your nieces.
This is going to sounds terrible but I slept with identical twin brothers and within 24 hours .. The situation is so complicated and doesn’t really matter to my question..
but now I want to find out who the true father is of my son. He’s 10 months old. I have access to one twin for DNA . Would my sample help if I only tested one twin? Is it even completely possible to find the TRUE father if I were to get BOTH of them to take the test? Is my sample important to the data?
Hi, Jolene. Unfortunately, a paternity test won’t be able to determine which twin is the father, since the brothers’ DNA is virtually identical.
Hi I had a dna test done in 1986 and it came back 96% the father but the question is could the child of been the baby said fathers brother how accurate was the test then
Hello, Alicia. There’s no question testing is much more accurate now than it was in 1986. If the brother of the tested party is another possible father, then it would be advisable to test again, if possible.
Hi there. My father passed away in 1999 and my paternal “grandfather” just passed away in feb 2021. I was told that my supposedly grandfather is not my dad’s biological father. Is there a way I can prove tbis by using my DNA and my late dad’s living siblings?
Hello, Monton. You do not mention if you are a male or a female, which makes a different to the answer to your question. If you are a male and your father’s siblings are uncles, you and they can do male lineage (Y chromosome) testing to see if the same Y chromosome is shared among men who are supposed to be from the same direct line. If you and the siblings are females, we do not have a test that can help establish a relationship for that scenario. You are always welcome to contact our experts directly for more information at 800-929-0847 and you can learn more about male lineage testing here: https://tests.dnacenter.com/relationship-testing/male-lineage/
I have siblings but i have a unknown different father and i would like to see if my sibling fathers brother is my father
There is only access between myself and a sibling
I wonder who Chris. Conan
How do you determine the biological father of a child in a case where cousins slept with the same woman and both men are deceased…?
Hi, Islander. The cousin relationship shouldn’t be an issue; there is more concern if the possible fathers share a closer biological relationship like brothers or father/son. The fact that both men are deceased makes a relationship determination trickier, but it can be done through family-reconstruction testing if enough other relatives are able and willing to participate. Call 800-929-0847 to speak with a DNA expert about options.
Can my child’s fathers half sister take a DNA test to prove paternity???
Hi, Ayanna. Half-siblings of an alleged father are not candidates for an avuncular test. I suggest you contact our experts directly to talk your situation through and determine if there are other options available to you. The consultation is free: 800-929-0847 (M-F, 8 AM to 8 PM Eastern).
I have a 4 year old daughter n her father might not b her father can I test the other man’s child against my daughter to see if they match
Hi, Sarah. You can as long as both you and the father of the other child can legally act on behalf of both children. I highly recommend that both you and the mother of the other child test too, if possible. If not, then you should definitely submit your DNA. Please contact our experts directly for more information or to order: 800-681-7162 (M-F, 8 AM to 8 PM Eastern).
Can a father be identified if the mother is deceased and the father could be one of two brothers or their father.
Hi, Victoria. That situation is definitely like putting together a DNA jigsaw puzzle. Without all the details about who all would be available to test, it’s difficult to provide an accurate assessment. I suggest you contact our experts directly to talk your situation through and determine what is the best course of action: 800-681-7162 (M-F, 8 AM to 8 PM Eastern).
If the fathers are brothers can conclusive results be had if only one of the males is tested?
-Prenatal blood/swab method.
Hi, Rowan. For prenatal testing, we cannot perform testing with two possible fathers who share a close biological relationship.
I tested my ‘Uncle’ and myself to see if we were father/daughter. I only had his and my sample, didn’t have my “dads”. Did the extended testing.
Got the results back today.
Says uncle is actually my dad.
Unformed of the results and he claims to have never slept with her.
But it was 34 years ago so i dont know what to believe. Only my family would have me doubting science.
So it says he is.. is he just in denial? Or what?
Hello! Did you inform the lab ahead of time that the other possible father is the brother of the man being tested?
My son and his first cousin could both be the possible dad of an 8mon old little girl only my son tested 99.99% the fater but being charged with sexual assault as to the 5 year age limit law between them well the cousin is a year older than he is but was wondering would that .01% of daught be a good fight to get things thrown out of court for his case
Hi, Jamilynn. Your son and his cousin don’t share enough DNA to provide a “false positive” for your son’s test.
It’s possible my first cousin is my half sibling. My father & his mother are blood bro & sis but now his father is possibly mine …. both fathers are deceased. How can we test to know if his father is also my father?
My niece has a child and not sure which brother is the father. Can she send in the DNA of the child, herself and one of the brothers for confirmation or would she have to send in a sample from both brothers?
Hi, Melissa. It’s absolutely best if both brothers can test as well as your niece. If only one brother can test, then it’s essential that the lab be notified ahead of time that the other possible father is the brother of the man being tested. That way, we can test additional genetic markers if necessary. In this scenario, your niece definitely needs to contribute her DNA as well. When she’s ready, have her call one of our experts at 800-929-0847 for a free confidential consultation.
Myself my daughter and her alledged father did a dna test which came back negative but he is identical to his brother and I have reasons to believe his brother took the test for him…because he doesn’t want to be her father… how do I figure out who took the test.
Hi, Terri. If you did a legal test, then the lab where you tested should have a photograph of the person who came to the facility for testing. You might start by inquiring with the lab.
Hi my husband did a paternity test and it came back saying in fine print. That they need potential brothers for testing. And he could be the avuncular of the child .What does that men&
Hi, Eileen. It means that data shows the father could be one of your husband’s brothers instead of him. They need to test as well.
A 30 year old woman contacted my sister n law saying that she’s related because she did ancestry .com she lived in our home town we new who her mother was and my husband and his brother were the only male members that were here at time so my husband summited his DNA to ancestry after his brother said he would but he didn’t so they said my husband was a 100 percent match is it possible it’s wrong since they didn’t have both dna
Hi, Laurie. You didn’t mention what type of relationship is being alleged. Is this a paternity case?