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!
My sister and I have the same mother(she has passed) but our father might not be mine. It is possible his brother is. Is there a way to find out if my sister and I have the same father without involving either or the brothers(our dad and uncle). I want to know but do not want them to know. And my sister is willing to get tested with me.
Hi, Jeana. What you are seeking is a full vs. half-sibling test. It’s unfortunate that your mother has passed, since her participation would have greatly optimized your chances of getting conclusive results. You and your sister can do a test, but it’s absolutely essential to let the lab know ahead of time that the possible fathers are brothers. This way the lab can take this information into account when doing their analysis and test additional markers, if necessary. Adding other relatives like your mother’s sister would be helpful too, but without your mother being available, you might get conclusive results but then again you might not. It just depends on your shared genetic data.
How much is the fee?
Hi, Sherry. A new legal test is $300-500, depending on where you live and other factors.
My boyfriend recently had a court ordered DNA test through DDC. The results came back as 99.9%. We also recently found out that the mother of the child may have (both parties deny this, but we’re suspicious) slept with his full brother around the same time of conception. Is it possible that the results were wrong? Also, is it possible to re-test the specimens?
Hi, Sherry. Brothers share 50% of their DNA only, so it’s unlikely that there was a “false positive” result. Yes, if indeed his test was done through DDC, since he did a legal test we can re-analyze the data, but keep in mind there is a fee for this service. Your boyfriend should call us at 800-681-7162 (M-F, 8 am to 5:30 pm Eastern).
What is the answer? Is it possible for a brother to get 0.00 on the paternity test of his brothers kids . My brother did a paternity test and it came back 0.00 % chances. That he is the father . But we were told it would show some percentage if he was the uncle. Does 0.00 mean no relation ?
Hi, Carey. In a paternity test, the lab answers a single question: Is the man tested considered the biological father of the child tested? The answer will either be 99.9% or higher or 0%. Nothing in between. It does NOT answer whether or not they are related in any other way.
If there is tow brothers (from the seam father and seam mother) and a Child. And we have test Only one of the brothers and the Child can be confirm this brother he is the father or not with out testing the other brother?
Hi. As stated in the article you’ve commented on, it’s best if both brothers can test, along with the child’s mother. If that’s not possible, it’s absolutely essential to let the lab know ahead of time about the other possible father and his relation to the man being tested. That way, the lab can take that knowledge into account when doing its analysis and extra DNA markers can be tested if necessary for conclusive results.
I want to know if dental fillings/pasta on teeths can affect the paternity results in any way? As far as i know fillings contains many chemical.
Hi, Roger. No, that’s not a problem and won’t affect results.
Hello! Is it possible to get a conclusive result in paternity test if one of the participant have a mutation(s)?
Hello, Grace. Analysts take mutations into account when doing their calculations plus they test additional DNA markers in order to obtain conclusive results.
Hello! i just want to know if its necessary to get additional paternity test when i get a conclusive result? ex. if i get additional 3 or more test is there a chance that the result came different from one another?
Hi, Vin. The results should be exactly the same for each test as long as the same DNA is submitted and the same ethnicity is stated. If you already got a conclusive result, you don’t need to do another anyway.
This is off my results papers,
Conclusions of DNA Paternity Test
Based on the genetic testing results obtained by PCR analysis of STR loci, the probability of paternity is 0.099% as compared to an
untested, unrelated random man of the Caucasian population (prior probability = 0.5). Please note that 2 mismatches (at loci D21S11
and D5S818) have been found in the comparison of the profiles between the alleged father and the child. Possible relationship
scenarios are as follows:
1. The Alleged father is not the biological father of the child or may be a possible relative of the biological father.
2. The Alleged father is the biological father of the child but there is a double mutation in the Child.
My questions are, if I have a 0.099% chance of being the biological father, why is it saying that I may be a possible relative? Just because of the other loci are matching? Is it fairly common for random people to have a lot of strings match? What are the odds/chance that a double mutation can occur?
Hi, Erik. Double mutations are not that unusual. I’m surprised the lab you used didn’t just take a little extra time to test additional genetic markers or include the mother in testing. Yes, because there are matches at all the other loci, that’s why they gave you the possibility of being a close relation (brother to the actual biological father, for example), although the chances of that are relatively small. Sounds like you need to contact the lab and ask questions about why they weren’t able to give you a more definitive conclusion.
If I have had a 99.99999 positive test but then find out that my Mum and Uncle had an affair, could my uncle be my father? When I sent my results back, I didn’t know this information so didn’t inform the lab that there may be another brother involved!
Hi, Tracey. You may want to perform another test, yes.
Me and an alleged father did a DNA paternity test few years ago and it came back negative. We do share DNA in 8 locations out of 15 (+ X,Y), in these locations:
D3S1358,
D2S1338,
D16S539,
D10S1248,
D2S441,
vWA,
D8S1179,
FGA.
Here are locations that we don’t share:
D19S433,
D22S1045,
D18S51,
D1S1656,
TH01,
D21S11,
D12S391.
I’m wondering if we are related and how closely.
I also did DNA testing with MyHeritage and one man shares 6,2% DNA with me that would make him my (paternal) great uncle or 1st cousin once removed or 2nd cousin. I contacted his sister (also through MyHeritage) and I’m pretty sure I figured out who could be my father by their family history/tree. I want to contact him but I’m terrified because he has no idea that he could be my biological father. My mother and alleged father were positive that they were my biological parents. I should ask this newly found alleged father to make paternity test but I don’t know how to approach him since he has his own family and quite high status job.
Hi, Erik. I cannot speak to results from ancestry companies, sorry. As for the paternity test you did, barring genetic mutations, you must match at every genetic locus tested in order for him to be considered your biological father. The fact that you share DNA in 8 locations means little and is not proof of a different type of biological relationship, like uncle or cousin. As humans, we all share a great deal of the same DNA: You and I probably match in many places. I wish you well with your search!
How probable is it, that both brother would match at all 20 locations in a test with a child? I mean in average.
It is unlikely, but possible. I cannot provide an average for you.
Hlw, I’m possible father of my own uncle’s son, shall we have to test of all three of us?
Hi, Binashak. That would be ideal, yes. And the mother should contribute her DNA as well.
Hi,
My husband was tested 21 years ago for a child with his ex. She(the ex ) also slept with his brother. Now the conclusion on the results said that my husband “can not be ruled out as” . what does that mean ? His brother has not been tested.
Hi, Mo. For the technology at the time, this was probably as conclusive a result as the lab was able to give. It means just that…your husband might be the father, or he might not. The lab could not say for sure that he’s not the father. Has he considered testing again, now that the technology is so much more improved? If he does, it’s essential that he tell the lab ahead of time that the other possible father is his biological brother. That way, the lab can take that information into account and perform additional testing, if necessary, to obtain a conclusive result.
Hello! I been having this gut feeling ever since my ex took the DNA test about 3 years ago that he is the father, but when he did the test, the results came negative, and he was very upset, there is another guy who I am having a problem contacting him to also get the paternity DNA test, I even got him into child support JUST for him to do the Test! what are the chances if my ex takes a second DNA blood test but this time would be him, my son(9) and me? I mean how different the tests are compared to the swab, and only taken by the alleged father and child? And also having the same birth marks can prove the alleged father is the one? (meaning my ex) even though he already took the test and it came negative?
Thanks!
Hi, Juliet. DNA collected via blood and via swab is exactly the same…one method is not more “accurate” than the other, in terms of results. If DNA for the same exact people who did the first test is submitted again for the second test, you can expect to see the exact same results, especially if you used an accredited and reputable lab like ours. A birth mark alone is not proof of biological relationship. All this being said, if you still have doubts, why not do another paternity test with your ex? I recommend doing a legal, witnessed test so that results can be used for court, if necessary.