Woman with Brothers

Testing “Brothers and Sisters” for Paternity

Over the weekend, the ABC show Brothers and Sisters aired an episode in which the two year old daughter of Tommy Walker needed a liver transplant.  In an earlier episode, when it was discovered Tommy was not able to father children, he asked his two brothers to donate so that Tommy and his wife could have a child.  With the liver transplant needing to come from the actual father, it was time to find out which of the two brothers was the biological father.

This brings up some questions that I am often asked.

-  How difficult is it to determine between two brothers, the paternity of a single child?
-  Does testing two brothers decrease the accuracy or probability of the test?

The truth is DNA testing is very accurate and unless the brothers are identical twins, the test will accurately reveal which one is the father.  The biological father’s profile must match the child at ALL locations or loci tested which is usually 15 markers.  It’s extremely unlikely that a brother would match a niece at all loci, unless he’s an identical twin to the brother. In that case their genetic profiles will be exactly the same and you wouldn’t be able to tell which one was the father.

In cases like this, we recommend testing both brothers (both alleged fathers) and include the biological mother in the test.  By including the mother’s DNA, we can identify which markers in the child’s DNA came from mom and focus on the DNA that must have come from dad.  If both brothers are tested with the biological mother, one will emerge as the biological father without question.

Any two people tested, even if unrelated, will likely share at least SOME markers in common, but a biological father and child will share ALL markers tested. Including the mother, testing additional markers or loci if needed and testing the other brother will identify more mismatches between the uncle and child and show stronger match between father and child.

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  1. I am a mother of a son who does not know if he is the biological father to a little girl. He is in jail and myself as a concerned possible grandma would like to know if the little girl is our family. Is there a way i can take a dna test in place of my son to determine whether or not she is his??

    • Hi Cinnamon,

      Yes, you would be able to take what we call a grandparentage test. If your son’s father is available to test with you and your grandson, this would be even better. This test is not avaialble at retail so you will need to contact us via phone to get one sent to you. Please call us at 1-888-404-GENE, Monday- Friday, 9 a.m.- 8 p.m. ET.

  2. Can you test two children of a deceased man? One youre sure belongs to a man against another who you are unsure of to see if he is the father of the second child? What is this test called?

    • Hi Sanaa,

      Yes, we do offer a test for this. It is called a siblingship test.

      If both children have the same mother and you want to find out if they have the same father we would do a full vs. half siblingship test which would tell you if they are full siblings (share the same mother and father) or if they are half siblings (share the same mother, but not the same father).

      If the children do not share the same mother and you want to find out if they have the same father, we would do a half vs. unrelated test which would tell you if they are unrelated (do not share a mother or father) or if they are half siblings (share the same father, but not the same mother).

      You will need to contact us to set this test up. We will be able to send supplies and instructions for collection and you will send us back samples for testing. Results will typically take longer than the normal paternity test. In addition, this test also costs more than our retail paternity kit. Please give us a call at 1-888-404-GENE to talk with us about which test would be best for your situation. We would be happy to answer any questions you have!

  3. Hi my brother passed away last year we had the same mum (also passed) and i was always told we had different dads but now i have been told its likely we had the same dad
    if me and my brothers daughter had a DNA would it tell me if me and my brother did have the same mum and dad,

    • Hi Michelle,

      We are sorry to hear of your loss of your mother and brother. If your brother’s father is known, it would be best to conduct a paternity test with him to determine if you share the same father, if however, he is not available or you are not certain that he is your brother’s father, we have other means to determine the answer to your question.

      We are able to test other family members to help with this question, called a family reconstruction test. We advise you to contact Identigene at 1-888-404-4363 and speak with one of our friendly client support staff members about what the best options you have. They will also be able to help you with pricing information and any other questions you may have about the testing process.

  4. Hi my name is Ovidia Lasley and me and my sister want to know if we have the same dad we ask our mom but she is lie to us my sister do not look like our dad and lot of people is tell us that we don’t have the same dad we just want to know the true please help us out with some answers we really want to know to know thank you so much

    God Bless

    • Hi Ovidia,

      Yes we have tests that can help you determine if you have the same dad. Since this test would most likely be a sibling test, and not a paternity test, it would be best if you contacted Identigene to find the best option for you. Our contact phone number is 1-888-404-4363 M-F 9 a.m.- 8 p.m. ET. We would be happy to answer all of your questions!

  5. is ther a way of knowing my dead brother’s real kid with my DNA?
    my brother’s dead body is not found.he passed away in war front.

    • Firstly, we’re sorry to hear of your loss. We appreciate his service and send condolences to you and your family. In regards to your question, yes, there is a way to know if your deceased brother has a child even without his DNA. The more people we have available to test from your brother’s direct family (parents or siblings) and if we have DNA from the biological mother the more likely we will be able to produce a conclusive result. This type of testing is called a family reconstruction, which means we take DNA from your brother’s family to reconstruct his DNA. Then when compared with the mother and child we can hopefully produce conclusive results. It would be best if you contacted our friendly client support team to discuss what family members are available for testing and which test would give the most conclusive answer to the paternity of the child. They can be reached at 1-888-404-4363 M-F 9 a.m.- 8 p.m. ET.

  6. There has always been a question as to who my younger brother’s father was. Both parents are dead. Me, my older brother, and my younger brother recently had a DNA test done. The results came back showing my older brother and I as brother and sister. But the test showed our younger brother was our nephew. What relation would the father of our younger brother need to be to make him our nephew? Could the tests be wrong?

    • Hi Patricia,

      From the information you have provided in your question, it looks as if a siblingship test was done by another laboratory. A siblingship test will tell you if you and your siblings are full or half siblings. A test like this will not indicate aunt, uncle or niece and nephew relationships. We suggest that you contact the laboratory who did your test and ask them to explain what your results mean. If you tested with IDENTIGENE, we would be happy to help you understand your results. Our phone number is 1-888-404-4363. Hope this helps with some of your questions.

  7. I have a question i am very curious about. If a half brother and sister ( who share the same mother but not father) have a child together ( a girl) how possible is it that a paternity test will be effective at proving hes the father? Is it possible that it will be inconclusive? What is it likely to say?

    • Hi Kellin,

      Firstly, you will want to call and inform the lab of your situation and that the mother and the alleged father are half siblings, as additional testing will likely be needed. If the test goes through and we find that half brother is not the father or he is “Excluded”, you will have a definitive answer that he is not the father. If we cannot rule the half brother out of paternity, the result may come back “Inconclusive” or “Not Excluded” (he is the father). If the results come back inconclusive, it would be advised to test any other unrelated alleged fathers for paternity. Hope this helps to answer your question.

  8. Hi I have a man that claims to be my fathers son…however my dad and the man took a dna test and it came back that he isn’t the father. Is there a way that he & I can take a test to see if we get the same results. He doesn’t believe the results he got between he and my father.

    • Hi Nita,

      The IDENTIGENE paternity test is for an alleged father and child, the mother is optional for testing. What kind of test was done with your father and the alleged father of the child? Was the child included on this test?

      In answer to your second question, yes, our paternity test kit sold at CVS, Rite Aid, Walgreens and Walmart is for the alleged father, child and mother. If you have any further questions about testing, please contact our friendly client support staff at 1-888-404-4363. Thank you!

  9. hi we are 1st cousin i am male and my cousin is female… and our fathers are brother. can we give some where with DNA test proof that we are cousin !! is it possible from DNA test?

  10. My brother just passed away and at his funeral , a sister to my brother’s son says she is my brother’s daughter. I got some of my brother’s hair and also managed to get a couple of hairs from her & her cigarette butt. Is there anyway to use what I have collected to see if she is my brother’s daughter?

    • Dear I.prince,

      We are sorry for your loss. Unfortunately, we can only test cheek cells with our DNA kits. You can conduct an online search for companies that DNA test hair, skin, glasses, utensils, etc. Best of luck! IDENTIGENE

  11. Hey

    I was wondering if you could help is it possible for me and a 1st cousin to be tested for half siblings we are most definitely 1st cousins as our mothers are sisters my father is now deceased so I would be provider of his dna we are both female or could it be possible to show inconclusive as of our mothers relationship

    Thank you in advance

    • Dear Iconfused,
      Yes, we can test you and your cousin to see if you are half siblings. Unfortunately, there is always a possibility for inconclusive results. You can improve your chances of a conclusive result if you test both mothers, your cousin, yourself, as well as any additional known siblings who have the same father as you. I would recommend contacting our client support staff 1-888-404-4363 to explain your needs. They will be able to recommend the best testing scenario for your situation so that our test has the most likelihood of producing a conclusive result. Hope this helps and good luck with your test!

  12. My brother had a child with his ex but the child doesn’t look like him or anybody in our family. The child now 12 looks exactly like another guy her mother was sleeping with. The problem is neither my brother or his ex wants to test her cause he doesn’t believe she cheated and she claims she didn’t. The other guy refuses to answer my question or get involved because of his current relationship. So I wanted to know if it was possible for me to test my nice with just sample from her and myself to see if we’re related. I really want to know because the child recently had a blood transfusion and her mother didn’t call my brother until after the procedure. This was extremely strange because she usually calls him even if she has a headache!!!,

    • Dear S. Darnell,

      We would advise you to contact our client support staff at 1-888-404-4363 to discuss your situation. An aunt DNA test is a possibility, however, the blood transfusion is a factor in testing. Client support can provide you with your options. Thank you.

  13. My sister and I have the same mother, who is deceased, and we are unsure if we share the same father. The other possibility is his brother (no they are not twins) However, my father is deceased also. If we take a DNA test would it be better to test us all three or will the two of them alone be able to get results back that show whether he is the father or not?

    • Dear Misty,

      This is a difficult situation but we could try and get you an answer of paternity. Our staff needs to know the situation so they can run additional DNA markers. Please contact us at 1-888-404-4363 and they can explain how a paternity test would work in your situation and what to expect for results. Thank you.

  14. Eight years ago, my fiance slept with his younger brother’s girlfriend. She was 18. His brother was 15 and he was 19. She became pregnant. She only had my fiance tested because she was afraid of being charged with statutory rape. The test results showed that my fiance shared DNA markers with the child, but not all. She did not disclose to the child support agency that his younger brother should have been tested so my fiance was named as the father. We have been raising the child half the time ever since. We recently obtained the child’s medical records and learned that the child was conceived two months prior to my fiance sleeping with her. We tried to get the courts to reopen the case and order another paternity test but they denied us. We feel that justice needs to be served for everyone involved. We don’t have a lot of money and his brother only wants to redo the test if it is done by a lab. He doesn’t really want to attempt the at home test. After reading your blog it says that my fiance would have matched on every marker if he was the father but he didn’t. How can we go about proving that his brother is the father without spending money we don’t have. We feel that she should be held responsible for lying to obtain benefits. Can you help us?

    • Dear Karla,
      We are so sorry to hear about your situation. Anytime there is a paternity question and the two alleged fathers are closely related, we recommend telling us this detail (explained in the FAQ section of the instructions) and recommend the mother’s DNA. We will also use more DNA markers so that we can achieve accurate results. Our lab is accredited for legal collections and I would recommend your fiance and his brother consider retesting through IDENTIGENE and upgrading to a legal collection. If your fiance is on the birth certificate, he will ultimately need a DNA paternity test to prove he is not the biological father and possibly seek disestablishment of paternity through the State. We recommend visiting your State’s government page and searching for guidelines for disestablishing paternity. There are strict time limits in some states.

      We hope this advice helps. Please tell your fiance’s brother, IDENTIGENE is a DNA laboratory and accredited by AABB, LAB, and NYSDOH for legal testing. He can expect the same testing procedures using our kit as he would if he used a local lab such as Quest Diagnostics or LabCorp.

      Please call our client support with any questions or to set up a legal collection. 1-888-404-4363. Thank you.

  15. I have a question. Can you email me your answer in case I don’t find the site again? Thanks.
    We, have always thought we were cousins. My mother and her daddy are siblings. We have been told that we may have the same daddy. Can tests tell us if we are half sisters if we are not cousins?
    Thank you so very much.

    • Rita,
      Yes. A sibling test can tell you if you are half siblings. Please contact our client support staff so that they can help get you set up with the appropriate DNA test to meet your needs and answer your relationship questions. Thank you. 888-404-4363

  16. Is it possible to determine if a girl is my half sister or my niece just only with her and my DNA. My niece grow up beliving my brother was her father but before her mother died she told my niece, her grand father may be her biological father. My father and brother are both deceased and my mom is out of the picture too..

    • Meron,
      A sibling test would be able to tell you if you and the other participant are half siblings. All we require is you and the possible sibling to test. The mothers are recommended but not required. Please contact our client support staff to arrange for testing. 888-404-4363 Thank you.

  17. Can a dna test determine if my exhusband is the father of my der sister’s son? The son in question is my sister’s older son. Born before we got married. I need to know if my daughter has a half brother or a cousin. If so… what test will be best and where?

    • Lisa,
      You will need the alleged father (your ex-husband) to test along with your sister’s older son in order to determine paternity through a DNA paternity test. If you would like to determine siblingship, you can take a sibling test (testing your daughter and your sister’s older son). Sibling DNA testing http://www.dnatesting.com/dna-paternity-test/more-dna-testing/sibling-dna-test determines if two individuals share one or both parents. DNA Testing with a possible brother or sister can help answer paternity questions when the possible father is not available to be tested. Half siblings share one parent. For example, a brother and a sister may share the same mother, but not the same father. Or, two sisters may share the same father, but not the same mother. When ordering your Sibling DNA Test, make sure you tell client support (888-404-4363) which test type you need. IDENTIGENE DNA testing experts help guide you through the process and answer all of your questions; both before and after the test.

  18. Also, would the three “children” or any of the serviving siblings of the deceased need to be tested? How accurate would the probability to determine parentage be? Thank you for your time and knowledge!

  19. You hit it right on the nose. The mother for the three “children” is the same for all three and she is still alive and able to provide a sample.

  20. Can i have a dna test done on me and my brother to see if his real father is my father as well?

  21. Is it possible to determine paternity if the “fathers” are brothers and both are deceased. There are 4 remaining siblings. However the plot thickens. Between the child’s parents- they have three kids. It is believed that the oldest child is one of the brothers offspring and the other two children are off spring from the other brother. I am needing to know how to determine paternity for the oldest child. Can this be done and how?

    • Gwen,
      I am forwarding this question to our lab director and I will respond with her expertise. Thank you for contacting Identigene.

    • Dear Gwen,
      Our lab director took a look at your questions and tried to answer but he wanted to make sure he understood the question to the best of his ability. First, please confirm:
      1) the 4 “remaining siblings” are full-siblings of the two alleged fathers (who are full-brothers),
      2) one of the two alleged fathers has two known children,
      3) the child in question (“oldest child”) is the offspring of either of the two alleged fathers and the question is which one.

      If all of the facts are correct above, then we would be able to address this with our technology, although since the two alleged fathers are full-siblings, there would be a good chance of an inconclusive result. In addition, we would also need to know whether the three children share the same mother, or whether there are two mothers, or three different mothers involved. Being able to also test the mother(s) would help tremendously to decrease the chance of an inconclusive result. If any of the three assumptions are incorrect, we cannot determine paternity.

  22. My son and daughter in law are having a baby girl.
    My daughter had a baby with my daughter in laws brother will both girls have the same D.N.A. ?

    • Dear Maureen,
      No. They will not have the same DNA. Identical twins are the only people that can have identical DNA. When people are related, DNA will indicate the biological relationship but they won’t have the SAME DNA. Hope this clarifies. Thanks for your question.

  23. my mother cheated on my dad around the time I was conceived she slept with his younger brother who is deceased how accurate would the DNA test be to find out which brother is my biological father? I have brothers from my “father” but we look NOTHING alike they have red hair blue eyes and are fair complected I have brown hair green eyes and olive complexion I know that doesn’t mean much but it was always a joke growing up till I was told in my 20′s that my dad most likely isn’t my dad. I have female cousins from my “uncle” they are olive complected, brown eyes and brown hair. My uncle had green eyes. Please advise

    • Dear Anonymous, Please don’t rely on facial features or hair color for paternity confirmation. If your father is willing to take a DNA paternity test with you, we can determine paternity even if the other alleged father is his brother. Identical twins are the only people that share identical DNA. You mentioned “younger” brother so they weren’t identical. Before sending in your swabs, please contact our client support staff and alert them to the other alleged father being related so that the laboratory has a note about the close kinship. Thank you.

  24. hi, i have had a prenatal test done on poss deff bio father came back 99.9% positive.
    i want to get another high loci test done on same possible father. second possible father is suspected half brother not available for test. i will be tested as well. could both half brothers matcj all locis (is it possible?), also if result comes back positive should i be happy with results? thank you

    • Kay,
      No, the only way brothers would have the same DNA and match at all locis would be for them to be identical twins. The father you tested is the correct biological father if the results were 99.9%.

  25. i slept with brother 1 in august, brother 2 on 1st august and 17 of august 2003. i cant remmeber m last period. however gave birth on april 11, 2004. how a dna can differiate the process

    • Dear Lisa,
      A DNA paternity test would tell which brother is the biological father unless they are identical twins. You can contact our client support staff to help guide you in the testing process. Our number is 888-404-4363. Thanks for contacting Identigene. Best!

  26. Hi,
    Is it possible to test myself and a cousin who is potentially my sister without our fathers DNA as they are both deceased. Story has it that we share the same father but need a DNA to prove this. We both have different mothers. Both deceased fathers are brothers. So in other words my biological father is suspected to be her father as well, but she has been raised to believe his brother is her father.

  27. I want to find out if my sister(with the same mother)& I have the same mother and father. Can I do that with samples from my sister, my mom & myself only?
    Getting a sample from her father is impossible.

    • Hi John,
      Thank you for contacting Identigene. The answer is yes. You would conduct a half vs full DNA siblingship test. You can contact our client support staff to learn more about this type of testing and to arrange for a kit to be shipped to you. Also, having your mom test will help strengthen the results. Our number is 888-404-4363.

  28. I am pregnant and am not sure which brother is the father. one does not know that he is potiently the father. When the baby is born if only one brother is tested, even if he is not the father will the dna test say he is?

    • Hello Mary,
      The answer is no unless the brothers are identical twins. When you are ready to take the test, please contact our customer service department and discuss your specific situation. We like to know that the two possible fathers are brothers. We also suggest you swab yourself along with the baby for the strongest results. Our number is 888-404-4363. Thank you for contacting IDENTIGENE.

  29. katisleidys martinez

    can i do an dna test with the dads sister ?

    • Hello Katisleidys,

      It’s always best to complete a paternity test with the alleged father and child, however, if the alleged father is not available you can choose the aunt/uncle test if the sister of the alleged father is a full sibling. For this test you would want the mother of the child to participate as well if at all possible.

  30. Hi..i have a funny but very important question.. If a dna test is done to prove father and daughter paternity. but the portential father is already a half brother to the daughter same dad different mom.. how can the DNA test determine if the half brother is the dad… i guest my question is if you are doing a pertenity test. For someone who already related as half brother and sister how can a dna show a brother is the dad.. its complicate.. i hope you take the time to answer my question

    • Hi Natasha,

      Thank you for your question. This is a very complicated situation, however, it is something that can be looked into. When you submit samples to the lab they do need to be made aware of the relationships. There may also be others that the lab would want to include in the testing as well. I would be happy to speak with you more about this.

  31. I would like to do a sibling test with my brother. Our Mother passed away two years ago, is there any chance that there may be any of her dna available amongst her belongings ie toothbrush, hairbrush.

    thank you for your time

    • Hi Tania,

      You can do a sibling DNA test with you and your brother to determine if there is a biological relationship. The best option would be to include any other full siblings you or your brother may as well. There may be a chance of your Mother’s DNA on certain objects, however, they are more expensive to test and there is no guarantee a profile will be found.

  32. Hi My name is nadia I’am from the Bronx, NY
    We are 3 sister from there mother and one father, my father DNA is very
    strong, everyone in the family look like in something, but one of my sister
    is completely different of us, we have some doubt because her mother used to be married when she got with my dad, I’m the oldest one and since my father is not around we want to find out if she is our sister.
    Can we do DNA between sister a least two of us, since both of us can to USA with a DNA test throughout Immigration department. and where can we get the DNA kit for that type of test.

    Thank u

    • Hi Nadi,

      Yes, we offer Sibling DNA testing. The best option would be to test all 3 sisters with any of the Mothers that are available. This is a more complex testing process. I would recommend contacting our client support team (they are wonderful and very helpful) at 888-404-4363 Mon-Fri 9am-8pm EST. They would be happy to assist you with getting everything set up.

  33. I am adopted and found both of my parents many years ago. I never had a DNA test with my father, but he said the story lined up and we let it go at that. He has now passed, and I have been told that my birth mother told him he was not my father. There is no way she will agree to a dna test, but I still need to know about my father. One of his children, my believed-to-be half-sister, is willing to do the dna test. His sister, my supposed aunt, is also a possibility. Who would it be best for me to take the dna test with … my half-sister or aunt? Thank you.

    • Hi Tracy,

      When the alleged father is not available for testing, you can choose the sibling DNA test or the aunt/uncle DNA test. Both of these tests will give a probability percentage, and are not as conclusive as a paternity test. However, out of the two I would recommend the sibling DNA test. For best results I would also recommend including her biological mother if she is available. You stated your Mom will not participate, however, we ask for as many biological mothers as possible to test as well.

  34. Dear Kay,
    My husband when he was 17/18 got two girls pregnant within a three month period. Boy 1 born 10/8/87 boy 2 born 3/24/88 (boy 2 birth date is approx not quite sure exact birthday) any way boy 2 was just now told that there is a chance that my husbands brother could be the father. My husband was tested way back when 2 was born and the results were 99.9% but is this new findings of the brother being a possability of paterinty? All are still alive what are the needed steps to find the true parent. After all these years my hubby has moved on gotten married and was just told this. He had dna done in the first place in 88 paid a lot of child support and medical bills for boy 2 and now she is telling her son my hubby might not be his true father but his uncle is. My husband is torn but would like to find out the truth and so would boy 2. Please and thank you for any help you can provide.

    • Dear Kristen,

      Thank you for contacting Identigene. When two alleged fathers are brothers, difinitive results are still possible. We always recommend testing both alleged fathers with the child. We also recommend testing the child’s mother if she is available. This does help in the testing process. If only one brother is available for testing you want to notify the lab a head of time.

  35. Hello,
    I had a DNA test taken to prove my father was my father when i was 10 (13 yrs ago). My sister (21 now) never had the opportunity to have a DNA test done to find out who her father is. My mother insists that my father ( we also have heard ‘rumors’ from other family members that it may be his cousin) is also my sisters father, and we have been trying to get him to take the test (even through a lawyer and all of that) but have been unsuccessful with getting his cooperation. My sister desperatly wants to know if this man is in fact her father. My question is…If my sister and I (share the same mother) took a DNA test, what are the chances of being able to tell if we share the same father also?

    • Hi Beth!

      You are in luck! The test you want, is a siblingship test (full vs half). In tests like this it is especially helpful to include your mother’s sample. Including your mother in the test will strengthen your results. If you have further questions, encourage you to call me (or any of our test consultants) at 1-888-404-GENE and we can give you more advice on your particular situation.

  36. Kate….My daughters father passed away before paternity was established can his half sister give accurate dna to establish paternity?

    • Hi Kristi,

      We can certainly do a DNA test to establish paternity with a half-sister. These type of tests we call “family reconstruction” tests, and they are a little more complex than a standard paternity test. With this type of test we are trying to “reconstruct” or determine what the alleged father’s DNA looks like, by using the DNA of his known relatives.

      You don’t mention if your daughter’s grandparents are available for testing. If either of them are available, that would really help. If he had another sibling to test, that would also be helpful.

      In short, I’d encourage you to call one of our test consultants. They would be able to talk to your about your particular situation so that you get the strongest possible result. You can call 1-888-404-4363

  37. can you take a test with you uncle to see if you have same father meaning my grandfather 2 o positives can not make an a- and my father is past and 1 uncle is past he was a+ and grandfather was ab- and aunt was o+ the uncle that i have living is a b these are all my father brother and sister and my grandma was o+

    • DNA paternity testing is done by comparing the loci (or markers) on sections of your DNA, not with blood type. While blood type can sometimes provide clues to paternity it won’t give you the definitive answer that DNA testing will.

      You don’t say which relatives are available for testing, so I would encourage you to call one of our test consultants to discuss your individual situation.

  38. I have a question. I had a half sibling DNA test done with a girl who I thought was my half sister.-same dad different mothers. It came out that they didn’t think we were half siblings according to the test. Is this the final answer? Is this test totally conclusive? It was like 59:1 or something like that. I have the copy of the results, but I just don’t understand it. Thanks.

  39. Dear Kate,
    I’m adopted and I’ve been contacted by a young lady who thinks I’m her sister. Is there a way to do DNA on the both of us to see if we’re related? We possibly have the same father. However, he passed away this week so we need to do the next step to find out. Thanks for your help.

    • Hi Sharon,

      The test you are looking for is a siblingship test. This test could be performed on you and the young lady to determine if you are half-sisters (share one parent) or are un-related. Only you and the young woman would need to participate in the test. It’s recommended to include DNA samples from both of your mothers, but it’s not necessary.

      You can read more about it here: http://www.dnatesting.com/more-dna-tests/sibling.php

  40. Dear Kate,

    Thanks for your answer. I put this question, because i made a paternity teste with my two childs, they are twins (not identical) and their mother. One of them give 99,9999% (child 1) and the other 99,99999% (child 2)so i was curious to know why was the diference. Even because the one(child 1) wich get 99,9999% is the one that is more identical to me. Both of them had that scenario in Penta D (mother has in a locci (Penta D) the alleles 9-10 and the child has in the same locci (Penta D) 9-10) but only child 1 had same scenario in D5S818, that’s why the probability of paternity was lower correct?
    I had a match with both childs at all 15 locations. So even with this scenario i have no reasons to assume that there is anyone else (even related) that can be the father of them, because according to your experience only the true father will macth all 15 markers, even with this scenario.
    Thanks in advance.
    Best regards.

  41. Hi Kate!
    Imagine that a mother has in a locci (Penta D) the alleles 9-10 and the child has in the same locci (Penta D) 9-10. In this case how do you know which allele come from the father? Could be 9 or 10? But according to your coments theres only one biological fahter that would match in ALL loccis and then you will know wich allele come from mom in this locci? Correct?
    I apreciate you would aswer this?
    Thanks in advance.

    • Hi Carvalho,

      Sorry it took me a bit to respond to your question, but I wanted to get some feed back from our Lab Director. This is what he has to say:

      “This is a very good question and the answer is quite simply, we do not know which Allele was given by mother but we can take this uncertainty into account in our statistical calculations. To explain, we need take a step back and understand how we account for such events such that we can arrive at a Probability of Paternity. To begin, each DNA marker that is used in a paternity test is given a Paternity Index (PI) which is a calculated value based upon the inheritance scenario and genotypes that exist. The PI reflects the weight of the statistical strength of genetic association given the discovered Mother, Child or Alleged Father genotypes. Broken down, the PI is simply a ratio of the test of two different hypotheses: Numerator (the probability that the Alleged Father of a certain race is the Child’s true biological father given the genetic evidence seen) vs. Denominator (probability that a random man of a particular race could be the biological father of the child given the genetic evidence seen). PI must be calculated for each genetic marker (CSF1PO, Penta D, Penta E, FGA, etc.). All PI’s are then multiplied together to get a Combined Paternity Index (CPI). The CPI is then converted to a probability of paternity (such as 99.99%). These are the highest-level of calculation steps that are performed.”

      I added a page to the site that walks though your scenario in in great detail. You can view it here:
      Understanding Paternity Index

  42. Dear Kate, Would a DNA test determine if my brothers have the same biological father that I have even though our father or fathers are deceased?

  43. I have just had a DNA test with someone I think is my uncle, however the test has come back “inconclusive”. The lab has offered an extra test but I am unsure if this is going to make any difference. Can an inconclusive test have any chance of coming back positive?

    • Dear Karen,

      An inconclusive result is just that: inconclusive; meaning that the lab cannot tell whether the person is the biological father. There is no way to know for sure without additional testing; inconclusive tests do not “lean” one way or the other. However, there is still a way to answer the paternity question.

      One common issue with inconclusive results is that the tested alleged father IS NOT the biological father, but IS RELATED to the biological father (and also related to the tested child, though not the father of the child). An uncle will typically share more DNA in common with a niece or nephew than someone else who is unrelated to the child. In most cases it is clear that the tested father is not the father but still related to the individual. However, in some cases the lab needs more information. The best option is usually to include the biological mother in the test.

      Remember, paternity tests work by looking for matches between your DNA and the tested father’s DNA. At every location the lab reviews, you (the child) have two allele numbers. One of these numbers comes from your biological father and the other from your biological mother. The biological father will match at all locations. Without the mother, there are TWO chances for the tested father to match the child at each location, because he can match EITHER of the child’s allele numbers. If the mother is included, the lab now knows which of the child’s alleles belong to the mother and which belong to the father. Now, the tested father has only ONE chance to match the child at each location. When the mother is included, the strength of any match increases because there’s a higher chance that the match shows paternity – the lab knows for sure that the match is consistent with the father because they eliminated the DNA that came from the mother. Also, there may be some matches that now become excluded (because the tested father matched an allele number that came from the child’s mother and not the child’s father).

      The strength of the matches determines the probability of paternity. If the probability is less than 99%, the test is considered inconclusive. Including the mother will make the result clearly fall one way or the other (but it’s impossible to know which way it will go until she is tested). Also, testing the other possible father usually helps, too. Often an uncle may show an inconclusive result but the true biological father will show a very conclusive result. In either case, though, including the mother helps strengthen the test results.

      For a detailed discussion about DNA paternity testing process and including the mother, please see these links:


  44. could you please tell me if its possible to do a dna test on a man and a woman who have different mothers but potentially the same fathers?

  45. I dated this guy (brother A) for three years. We broke up and occasionally had sex. I stopped having sex with him and about a month-two months later I went out to the bars with his brother (brother B) and we ended up having sex a couple of times when we were drunk. I then found out I was pregnant. We had a paternity test done with me, my daughter, and brother B. The test results were 99.89 %. We never had brother A tested and now I am starting to wonder if I made a terrible mistake not having him tested. Is it possible that brother A could be the father?

  46. Can you tell me if I can have my sister and I tested to see if we have the same father without testing anyone else? I am 42 and I was 41 when my mother admited that my dad might not be my dad. I do not want to hurt the man that I have grown to know and love to be my father. Please advise.

    • http://www.dnatesting.com/more-dna-tests/sibling.php

      Neva, you certainly could! What you would want to do is a Full vs. Half siblingship test. When doing this test, it’s best if you can include your mother. This will strengthen your result.

      The test can still be done with just you and your sister, how ever it is possible that without your mom, you could have an inconclusive result.

      Because you and your sister (or half sister) both received DNA from the same mother, including your mom in the test will allow us to isolate the DNA that comes from her to be sure we are comparing the DNA that you and your sister received from your father.

  47. My grandmother slept with two men who were brothers. My mom was born shortly after. Then my uncle & two aunts were born. They were all raised believing brother A was their father, but once he passed, the family started saying that brother B was my mom’s real father. Problem is, both brother A & B are dead. Brother B has a son as well, so is there a way for my mom to compare her dna with that of my uncle, aunts & her “cousin” (who actually might be her half-brother)?

    • Hi Natalie, Your mom could do a DNA siblingship test to determine if her brother is her half-brother or full brother (this would be a “Full vs Half Siblingship” test.) When doing DNA relationship testing, it’s best to use the closest (biologically) relative, and in this case, that would be one of her siblings.

      When doing these kinds of tests, it is especially helpful to include the biological mother (your grandmother). If you have specific questions you can call one of our test consultants at 888-404-GENE.

  48. Philomena: It’s difficult to say. The best choice, when looking for definitive results, is to test EVERYONE. Including the mother would strengthen the result. Including the other brother as well would help even more.

    Nikki: That’s a good question. If the test comes back that your husband is excluded as the father, the only thing to know for certain is that he is not the father. If your husband and the child match at several locations, it’s possible that your husband shares those markers with the child’s father. However, it could be because he and the child’s father are related, or it could be that those markers are just very common.

    Becky: The short answer is that you need a half vs. full siblingship test. This would test both your daughters, and yourself, and would give you the probability that your daughters share the same father. This test however isn’t as conclusive as a paternity test, and would give you only the LIKELYHOOD that they are full siblings. Siblingship Tests CAN be inconclusive. A paternity test would be less expensive, and would definitively exclude one man from being the father of both girls (with 99.99% certainty).

  49. hi i have two daughters and would like to prove they dnt have the same father, at the moment i cant get the fathers to do a paternity test and im unsure which test i should now do to prove this. could u advise me of which test i should get? thankyou

  50. My hubby was tested and the results came back positive. I am not sure if they tested her mother, but we are suspecting that his brother messed around w/ her as well. I am paying for another dna test for my husband and her but if this comes back negative would they be able to tell if it were a family members dna? If they were close to matching?

  51. So, If two brothers were suspected to have possibly been a childs father and one brother had test done and results were 91.7%, would you say that he was the childs father?

  52. So my dad was with this lady and she got pregnate but my dad thinks its his brothers. So my dad got a paternity test just with him and the child and it came up as 99% could it be his brothers?

  53. I apologize that I did not get back to these comments sooner. Mandy it is difficult to speculate whether Avuncular testing might return low results like yours when their sibling is in fact your father. Because siblings only share a certain amount of DNA Avuncular testing can sometimes give results that one might not expect.

    Matt: If the biological mother is tested it does help with the conclusive nature of the testing. However, we would still appreciate being informed of two alleged fathers being brothers to ensure all proper protocols are followed to provide accurate and conclusive results.

    Dee: With results that high I would say that the father tested is the biological father. However, if you still have concerns I would suggest having a DNA test done on the other brother.

    Charlie: It can be difficult to tell cousins and half siblings apart. This is because there is already an established biological relationship. If there is a male half sibling the best test I could recommend would be a Y-Chromosome test as this will only test if the two share a common male ancestor. You can find these tests on our website.

  54. Here’s the story…My husbands mom and aunt were both married to the same man. That man is possibly my husband’s father but is not the man who raised him. This man is now dead and my husband is wanting to know if his cousins are actually his cousins/half brothers and sisters by the same father. Is there a way to know since they would have genetics in common through their moms being sisters and the father now being dead.

  55. what does one do when two brothers are alleged fathers, but only one was named as the father, tested 99.9. Should I be satisfied that he indeed is the father or maybe his brother is the father.

  56. You said “If only one brother is tested and the mother is NOT tested, there is a possibility (extremely small) that he could match the child at all locations”.

    What happens in this case: two brothers (not twins) had sex with the same girl. Girl tells brother A that he is the father but brother B is the actual father. Brother B is unreachable and brother A wants to make sure he is the father so he gets a paternity test. Both brother A and the girl are available for the testing. Does he need to inform the lab technician about this situation? And how accurate could the results be? What kind of result would he need to get to be sure that he is not the father?

  57. Is it possible for an avuncular test for two aunts to come back in the really low probabilities, i.e. 2% and 14% probabilities, if the biological father is indeed my father??? We assume the siblings all share the same parents. We have not done a DNA test with the father’s DNA, and I was astounded with these low results from testing the two sisters of my father. Is this enough to make a paternity conclusion that my father isn’t really my father?

  58. If testing is done and it is found a man is not the father, and then it is discovered his brother was sleeping with the same woman, what is the probability of the child being his since the test came back negative on his brother?

    • Parker, I apologize, but there is no fixed probablity to give you in this situation. Even though one brother was excluded as the father that does not automatically exclude the other. Both would need to be tested to prove that they are in fact not the father of this child. I hope that this information will be helpful.

      • I tested my father’s DNA and it stated that
        we were 99.9% related, is it still possible
        that my uncle could be my real father?
        Both brothers have passed away and
        there is no way of getting DNA samples
        for further testing, is it forever a mystery

        • David,
          Thank you for posting on our blog. Are your uncle and your biological father identical twins? If so, their DNA is identical and we would not be able to confirm paternity. If not, we would be able to determine paternity, even with close relation. When you tested your “father”, did you include the mother in the test? Did you tell client support that there was a chance that your uncle could be your father? If you have a case #, I would be happy to pass it along to client support and they can contact you and speak with you about your results so that you have peace of mind with your results. Best, IDENTIGENE Social Media

  59. You are welcome to post the article on your site as long as your provide me with proper credit for writing the article. Please also include a link back to my blog. Thanks

  60. I really very liked this post. Can I copy it to my site?
    Thanks in advance.

    Sincerely, Timur Alhimenkov.

  61. Sure, you can do a DNA test between an uncle and a child. We call this an Avuncular DNA Relationship Test. This will show the probability of a relationship between the father’s brother and the child. This test is $495.00 and can take two to four weeks to complete. If you would like more detailed information on this type of testing you can visit our website at: http://www.dnatesting.com/dna-test-relationship/avuncular-dna-testing.php or contact our client support team at 888-404-4363.

  62. If the suspected biological father is deceased, would it be possible to test his brother to determine if the child shared DNA with that family?