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!
It’s possible that my dad’s brother is my biological father. They are both deceased. Would a sibling dna test determine if I have the same father as the sibling?
Hi, Cathy. I suggest you contact one of our experts directly since the possibility of obtaining conclusive results depends on who can participate in the test along with a variety of other factors. That number is 800-929-0847 (M-F, 8 AM to 8 PM Eastern).
I had sex with a guy October 24th and 31st. My period started October 30th. And I had sex with my boyfriend the 13th, 15th, 20th and 26th of November. I found out I was pregnant November 29th and had pink spotting mixed with discharge on November 27th. I had a ultrasound on December 31st saying I was 8weeks6days. Could the guy from October be a possible father?
Hi, Leena. That is a question best answered by your doctor.
I have a 1year and 7months old baby and the father is dead and the father is a us citizen i don’t know how how i can get a dna result to file for her us passport
Hi, Lawal. I suggest you contact the U.S consulate or embassy where you live and ask them. Hopefully they’ll be able to help.
I just found on out 23&me that I have an uncle who would make his brother my uncle. His brother was adopted. But on his family tree it says I am his half-sister. Which would possibly make his dad my dad. His dad had a twin brother (non-identical) Could it be possibly the fathers twin brother is my dad? How would I be able to find out? Is there a more comprehensive test if just the Unlce/Half brother would be willing to do DNA? So confused.
an uncle who would make his brother my father*
Hi, my question is, if all parties involved are deceased can you test a cousin to see if you are actually brothers?
Mom may have had a one night stand with her brother in law and I think the brother in law is my dad.
My uncle, his wife, my mom and dad are all passed. My uncle has a living son, is there a way of him and me testing to find out if we are half brothers?
Hi, Rich. Yes, you can do a half-sibling test. Contact us directly for a free consultation at 800-929-0847 (M-F, 8 AM to 8 PM Eastern).
Hi my cousin and brother both was having sex with the same girl my brother had a test done to see if the child was his son they said yes but the child looks more like our first cousin how can we find out. Thank you vickey
Hi, Vickey. A first-cousin relationship is too distant to result in a “false positive” for your brother. Physical characteristics are subjective and therefore are never absolute proof of paternity.
Hi, Jennifer. Your situation is a complicated one that requires more information from you about who’s available to test, etc. For this reason, I suggest you contact us directly at 800-929-0847 so that one of our DNA experts can assist you one on one. Good luck!
My dad or my uncle could be my sister’s dad, my uncle has passed away.
I was wondering if my sister and my cousin (her dad is my uncle (fact)) were to do a DNA test, could this tell us if my uncle is possibly her dad? We don’t want to involve our dad at this stage unless we definitely know he needs to do a DNA test
Hi, Anon. There are a lot of factors in play here, such as whether or not the mothers of the two parties are available or willing to test. That could make a big difference. I suggest you contact our experts directly to talk it through and determine the testing scenario that would work best for you: 800-929-0847 (M-F, 8 AM to 8 PM Eastern). The consultation is free and there’s no obligation.
So if a guys test came back saying he is 70% is he the father
Hi, Kathy. No; that is considered an inconclusive result. With today’s technology and advanced testing systems, there is no reason why any lab should return an inconclusive result if a paternity test was performed between a possible father and child.
For the last 43 years &7 months. I thought one man was the father of my son. I put him up for adoption when he was born. A year ago he found me. What I thought was his father all his life had died. I kept in C touch with his fathers brothers as we all grew up in the same little town. Since then I took a DNA test that proves I’m his biological mother at 49.9 % and I his father is 51.1%. What I thought for all this time as being his biological brother and cousin, they said they took the test an they said they were not a match. Since this happened my son has kept searching for his biological father. I told him I’d help him in anyway. My son said he found a lady in Oregon that is 12% his relation. What part of the connection would she be? Could I have the brother of the man that I thought was his father take a DNA test would it b prove he was his Uncle?
Hi, Mesue. A 12% connection with the lady in Oregon sounds like a cousin. Yes, your son could do an avuncular test with the brother of the alleged father. You should contribute your DNA as well. I suggest you contact us for a free confidential consultation at 800-929-0847 (M-F, 8 AM to 8 PM Eastern).
Hello, I have a 3-year-old girl and am in a confusing situation. so my daughter has dimples on both cheeks, but neither I nor my husband has dimples in our families both mum or dad’s side. My husband is also a second cousin from my mum’s side. there is another man who has dimples in his family who could be the possible father of my child. I had a paternity test taken with Me Baby and my husband and the result was positive 99.99% for the father but am not sure if this result is positive cause my husband is my second cousin. I really doubt this cause was told by a friend dimples occur only in families hence I feel this other man could be the father. Is there any test that can prove this??
Hi, Stella. Unless the untested man is a close biological relation to your husband, then there is no need to test. Dimples are a genetic mutation; it may be that the trait is in one of your families way, way back, or your daughter has her own mutation. It’s not scientifically sound to use this trait, or lack of the trait, as a determinant of a biological relationship. DNA is the only sure way to determine paternity.
Paternity test q.. 2 brothers from one mother
The mother was married to father #1 and she had sons hereafter called son1 and son2
There are 2 possible fathers for son #2 which could be father #1or father #2.. and they were brothers
Both possible fathers are now deceased and the only other living sibling is their sister
Now there are no known available dna samples for father 1or 2since both have been deceased for years. Also of the son1 and son2 they do NOT get along so obtaining a dna sample of brother 1 in theory is possible butpote totally problematic
DNA from son2 the mother and the fathers living sister are easily enough to obtain
Now the easiest way I thi k to determine son2s fatherwould be comparison of dna with son1 whom is known to be father1s kid.
Besides that obvious comparitive is there another potential way given this available dna info to determine if son2 is the son of father1or his brother father 2
You’re right that the best way to determine son2’s father would be to test him with son1. Since that seems unlikely given that they don’t get along, I suggest you contact us directly to speak to one of our experts and see if there is another viable option: 800-681-7162 (M-F, 8 AM to 8 PM Eastern).
So I have two nieces and my sister slept with two brothers and their father meaning the two girls grandfather. The girls have been curious to know if they share the same father and got a DNA match. Does this mean that only one of the brothers is the father or is it possible that the DNA is shared between the two brothers or a father and either one of them could be the paternal father?This all happened a few years apart so nobody really knew at the time what the real situation was. The girls just do a DNA test and they’re assuming the one brother is their dad. Is it possible the grandfather for the brother that she slept with before they were born to be a DNA match to one of them
Hi, Pamela. Did they do ancestry testing? What do you mean by they “got a DNA match?”