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!
Hi I have a daughter. I doubt that her father could be my brother’s son. He is not agreeing to give his DNA for testing. Having testing between me and my daughter will give a correct result?
Hi, MC. Yes, you will get a correct result. But in a case like yours, it’s essential to let the lab know ahead of time that the other possible father is your nephew. This way, they can take that information into account when doing their analysis. It’s also best if the mother of you daughter also contributes her DNA. For a free consultation, contact us directly at 800-681-7162, M-F from 8 AM to 8 PM Eastern.
I’m helping a friend search for his parents as he was adopted as a newborn. Through Ancestry I’ve managed to find his birth mother, but she is unwilling to talk/meet. I have also narrowed the paternity to two brothers, both deceased. They were not twins. Only one brother had children, but I have been unable to reach them for a conversation. This leads to a few questions… if the potential first cousins/siblings are DNA tested will this confirm my friend’s paternity (even without the birth mother submitting a DNA sample)? If I am unable to chat with these potential relatives, is there a way for your company to reach out to the potential relatives on a client’s behalf? It’s not impossible for me to reach these relatives, but I do not want to apply pressure or shock them with the potential news since I’m a complete stranger from a neighboring state with information they either have a brother or cousin they (and very likely their father or uncle) knew nothing about. All information appreciated.
Hi there, DeWayne’s Friend. You are kind to help him out. We could definitely do sibling tests with any potential relatives who agree to testing, although it’s optimal for conclusiveness to have the mother submit DNA too. Short Tandem Repeat (STR) analysis, which is the type of testing we do, does not identify cousins: only closer family relationships. If any of those potential relatives are males, we could see if they share the same data on their Y chromosome as DeWayne. The Y chromosome is passed on from father to all sons and can help in situations like this. You can learn more about it here: https://tests.dnacenter.com/relationship-testing/male-lineage/
We do not reach out to people on a client’s behalf…that legwork is yours or DeWayne’s to perform. But once everyone is ready to test, then we get involved.
All these Jerry Springer episodes and I have 1 of my own. Long story short- My brother and I ended up sleeping with the same woman a few days apart. I found out a year after my daughter was born that this had occurred . I was still seeing the mother. We went for a court ordered dna test. I was extremely hungover and she made out with me in the parking lot for several minutes. I always thought it was odd that she kept rubbing my inner cheeks with her tongue (which she had never done before or since.). Only recently did it occur to me what she was attempting to do. My brother was in prison at that point, so I was the only 1 tested. 99.1% the father. It was explained that my daughter and I had a match in all but 1 of the tests, so I was the father. I found that test result paper a few years ago and just happened to look at it again. According to those test results, the mother and I also had a match in every test but 1. My daughter is now 22. I don’t want a medical issue to come up down the road like an organ donation or something and we find out at that moment that we’re not father/ daughter. I realize a new test would answer my questions, however my daughter is unaware of the situation and I don’t want to unnecessarily cause her panic. I don’t know if her mother’s actions actually contaminated the test result (as I believe she intended to do) or if I’m being paranoid? FYI, the DNA test was done in 2002.
Hi, Edgar. Without seeing the data from this test, it’s very difficult for me to provide any kind of feedback about its particulars. More than the “licking cheeks” incident, the fact that your brother is also a possible father is definitely a concern. If the lab was not aware at the time of the possibility of your brother being the father, then they would have no reason to conduct extra testing to ensure a correct result. I cannot give you advice on how to explain to your daughter, but to put your own mind at rest it may be wise to test again. The technology is so much better now, but it is still essential to let the lab know ahead of time that your brother is also a possible father. It may very well be that you are her father and that your worries are unfounded, but since this is still nagging at you nearly two decades later, this may be an opportunity put your heart at rest.
They didn’t know at the time my brother was a possibility, but I called a couple years later and spoke with someone at the center. They told me my brother should have been tested too, but that it wouldn’t change the test results. I’ll look into getting us retested, somehow Thank you.
You’re welcome and good luck!
Two men who are double first cousins. Both could be the father of my son. Only one of the double first cousins has agreed to be tested with my son. Will the test be able to determine if that double first cousin is the father?
Hello, Jean. Most likely yes, but the lab would need to be notified AHEAD OF TIME of the biological relationship between the two possible fathers and you should definitely contribute your DNA as well. For a free consultation, please contact our team of experts at 800-681-7162 (M-F, 8 AM to 8 PM Eastern).
I am 56 and have a possible sister that my dad does not claim. I would like to know for myself. There is a possibility that the father could be my dads brother. Will a DNA test with me and my possible sister give an inclusive answer?
Hi, Michelle. If both your mothers are available for testing, that would be extremely helpful. I suggest you contact our team of experts to talk through the possibilities for tested parties and what you might expect from results: 800-681-7162 (M-F, 8 AM to 8 PM Eastern).
Hi, I’m wondering if DNA testing could prove who the father is of my grandson (son)? During an on-off relationship with my youngest son, the mother had sex with me, my oldest son and my youngest son in the space of 2 weeks. What would be the criteria for testing to be conclusive?
Hi, Nick. All three men and the mother would need to contribute their DNA for testing and the lab would need to be informed beforehand of the men’s biological relationship. For more information, contact our DNA experts directly at 800-681-7162 (M-F, 8 AM to 8 PM Eastern).
I’m concerned that the two boys my girlfriend says are mine may actually be my brother’s. We are same father, but different mothers. I know for sure that he won’t agree to a dna test & it’s likely my girlfriend won’t either, if I bring up the matter. Could a test prove beyond any doubt who the children’s father is ? I just need to know for sure.
Hi, Ben. As long as the lab is notified AHEAD OF TIME of the biological relationship between you and the other possible father, they can test as many additional DNA markers as necessary in order to obtain a conclusive result. It’s always best if the mother of the children contributes her DNA, especially in a case where the possible fathers are related. I highly recommend that you contact our team of experts to talk your situation through and determine what might be your best option: 800-681-7162 (M-F, 8 AM to 8 PM Eastern).
I recently did a paternity test. The test came back with a 99.9999999% probability of me being the father. However, I did not notify the lab of the other possible father in question is my first cousin. Would this void the initial results of 99.9999999% of me being the father?
Hi, Doug. No, you don’t share enough DNA with your cousin for it to affect results in any way. You’re fine.
I recently did a half/full sibling test on my son and daughter the result came back as 99.99% full sibling. my husband now wants a paternity test. will the results change? I also submitted my daughter’s sample to dna ancestry and my husband also submitted his (2 years ago). my husband does not appear as a match on my account with my daughters info
I’m so confused
Hi, Abby. I suggest you contact our experts for a free consultation at 800-929-0847. It sounds as if there’s a missing piece of the puzzle.
My brother and I (only siblings) as well as 6 cousins all come from 3 brothers. there is some confusion perhaps as if there is some affairs between the brothers and the others wives. all of the brothers are dead, but all the second generation remain. what would be the best way to ascertain if “everything is order” as to how the kids are assigned to the brothers? Some of the cousins don’t speak to each other.
Hi, Raymond. Yours is too complicated a case with too many variables to provide an adequate answer in a blog comment. I suggest you contact us for a free confidential consultation with one of our experts at 800-929-0847.