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 and she has 2 possible fathers, they are brothers as well. I had her july 8th and the conception date was October 16th and I slept with them both within the week though. I have to get a paternity test on the 22nd. I need to know. What will happen if the one that is getting tested isn´t her father and how much of a possibility is it for them both to have very close DNA..
Hi, Rayven. Regardless of conception date or who you think the father might be, it’s ABSOLUTELY ESSENTIAL to let the lab know ahead of time that the other possible father is the brother of the man being tested. That way, they can take that information into account when performing the analysis and test additional genetic markers, if necessary. You should also contribute your DNA. Ideally, both men should be tested.
Hi, me and my dad where tested, with the 20 loci test. The result was 99.99999998% (matching on all locis) and the combined index was 6,582,606,282. My unce, who deceased, could theoretically also be the father.
In your article it says “The chances of two brothers who are not identical twins matching a child at each genetic marker for paternity testing are not likely. ”
With the numbers above given, could you give me an estimation of how probable it is, that my uncle could have been the father? It should be almoust impossible, right?
Thank you
Almost impossible, yes.
Thank you very much!
Would it be possible to guess any percentage range? For ecample: Is the possibility less than 1% or more like less than 0,00001%
Without all the data, I cannot provide a percentage range, no. Sorry!
My ex took a test it came back less the 100% his brother is now taking a test would the rest of that percentage likely be the brothers
I’m then mum so I know I make up for a part of it but I’m very confused one is older then the other I’m hoping that I can get the answers
Hi, Anonymous. A probability of paternity for paternity test can never be 100% since DNA testing is based on statistics. So without also testing every other man in the world with the same racial background as your ex, the highest probability of paternity is 99.9%+. If the test show a probability of relationship of 99% or higher, then your sons are considered your ex’s biological sons.
In this scenario the father could be a son or his dad.
There is a lady who we have always considered my half aunt (my grandfather’s daughter) but there was a chance she was my father’s daughter as well making her possibly my sister. My grandfather (when my dad was a teenager my dad’s father) had an affair with my dad’s girlfriend and she became pregnant with said lady. Both my grandfather and my father have passed now. How/who would we get tested to get the most accurate results?
Hi! You didn’t mention whether or not the lady is willing to do DNA testing. If she’s not, then the issue is moot. If she does agree to testing, I suggest you contact our experts directly to determine how to best proceed. That number is 800-681-7162 (M-F, 8 am to 8 pm Eastern).
My mother had 2 possible fathers. Both of whom are deceased. My mother does not want to know who her bio father was. However due to medical history, I feel its important for me and my children to know who my grandfather is.
Can I take a dna test with one of her possible paternal siblings to find out if he is my uncle? They do not share the same mother
Hi, Tina. Yes, you can do an avuncular (aunt/uncle) test, but keep in mind that the chances of obtaining conclusive results would be much greater if your mother participated. This is further complicated by their being half and not full siblings. I suggest you contact our experts directly at 800-681-7162 (M-F, 8 am to 8 pm Eastern).
My son and the alleged father was tested and the results came back “0” but I was never tested. Should I reconsider retaking the test so I can be tested as well. They have the same numbers on some of the markers
Hi, Lashawn. Unless the lab requests it, your participation is not necessary. Because we’re human and we share a lot of the same DNA, it is not unusual for people to have some of the same data at different genetic markers. You and I probably do too! What’s most important in paternity testing is for there to be matches at all genetic markers. Sometimes there may be one or two mismatches due to genetic mutations, but those are taken into account during analysis.
My ex wife told friends that my father is my son’s father not me, my has passed away and she refuses to be apart of any genetic testing, can i have both of my sons dna tested along with mine to find out?
Hi, Ronald. Yes, you can. Just be sure you specify your sons’ possible relationship with your dad when ordering the test. That way, we can keep that information front and center during the analysis and then test additional markers, if necessary. Call us for a confidential, no-obligation consultation at 800-681-7162 (M-F, 8 am to 8 pm Eastern).
Hi if the alleged father is tested and he is a first cousin to the mother and the results say he is 99.99999999%, is this accurate? Will the mother and tested fathers relationship as 1st cousins affect the DNA results if the lab are unaware of this relationship?
Thanks,
Lou
No, a first-cousin relationship is not to worry about since they only share about 12.5% of the same variable DNA. We’re more concerned with a father/son, nephew/uncle, grandson/grandparent relationship. As stated in the article you commented on: “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.”
If alleged fathers are father and son. And one of them had a negative test result with the baby. Is it 100% that he is not the father for the child?
Hi, James. Yes, it is.
Adding to my question above..
Since I did a legal Non-Invasive prenatal test can DDC take another look at my results and see to make sure I couldn’t be a distant relative to the child? I am the only one who can be tested. or do we have to re-test..
My moms sister and my dads brother had a child. I don’t believe my son is mine, I believe he may be my cousins. He will not take a test. So I’m asking if myself and my son took the test, would this be accurate? Could it be possible that our DNA is that similiar? Or No?
Hi, Christy. I’m confused by your name. Are you the mother of the child or the alleged father of the child?
I sent in child’s sample and 2 possible fathers samples in one envelope. The results have been posted and 1 shows as the father @ 99.999 but I was not given the name I provided on the envelope. Only a number for the sample. How do I determine which person is my father?
Hi, Terri. If your test was with DDC, give us a call at 800-831-1906 (M-F, 8:30 am to 5:30 pm Eastern).