Are they really my parents?

Are they really my parents?
Are they really my parents?

If both of my parents have O positive blood, is it possible for me to have O negative blood? I have been told that it is not possible, that one parent would have to have the negative factor. I have been researching this question for some time with no good answer. I would really appreciate your help in answering this.
Debbie Howlett – Farmington, New Mexico


Dr. Greene’s Answer:

Genetics can be so confusing! I can easily see how after much research the issue would still appear murky.

The modern science of genetics had its start in 1866 when an Austrian monk named Gregor Mendel provided a simple yet powerful description of how traits are passed on from one generation to another. Mendel’s work was unappreciated until 1900 — more than fifteen years after his death. In his initial formulation, he described how sexual beings get two genes for each trait, one from each parent. The trait expressed, or visible, is a result of the interplay between these two genes. Specifically, he recognized that some genes are dominant and some are recessive. If you have one copy of a dominant gene you will express that trait, regardless of the other gene. In order to express a recessive trait you must have two recessive genes.

Mendel’s first experiments, though simple, were quite profound. He worked with peas, which had easily distinguishable traits, such as green versus yellow seeds. Each pea has two seed-color genes, one from each parent. The peas with two yellow genes were yellow. Those with a yellow and a green gene were also yellow; only those with two green genes turned out to be to green. Thus yellow was dominant over the recessive green gene.

The situation with human blood genetics is far more complex, since at each point there are multiple possible characteristics. Nevertheless, the genetics of human blood is far better understood than that of any other human tissue. While there are rare exceptions, the following information on blood types applies to most people.

First, let’s look at the ABO blood types. Each person receives an A, B, or O gene from each parent. In this system, the A and B genes are co-dominant and the O gene is recessive. Thus, a person whose genetic type is either AA or AO will have blood type A, those with genetic type BB or BO will have blood type B, and only those genetic type OO will have blood type O. This means that a child with type O blood could have parents with type A, type B, or type O blood (but not with type AB). Conversely, if two parents both have type O blood, all their children will have type O blood.

Another medically important blood type is described in the Rh system. These genes were first discovered in the rhesus monkey, hence the designation Rh. The Rh system is actually far more complex than the ABO system in that there are 35 different possibilities that one could inherit from each parent. These, however, are roughly grouped into positive and negative types. In this system the positive are dominant over the negative. If your genetic type is ++ or +-, your blood type will be Rh positive. Only if your genetic type is — will you be Rh negative. This means that if both parents have Rh+ blood with the +- genes, they could have children who are ++, +-, or –. In other words, their children could be either Rh positive or Rh negative. Children who are Rh negative can have parents who are either Rh positive or Rh negative.

Two parents who have O positive blood could easily have a child who is O negative. In fact, most children who are O negative have parents who are positive, since the +- combination is so much more common than the — combination.

As it turns out, there are more than a dozen complete blood group systems other than the ABO system and the Rh system. This makes great precision possible in looking at inheritance and family trees.

There is no reason, based on your blood type, to suspect that your parents might not really be your parents. If questions linger for other reasons, specific tests are available through blood banks and private laboratories that can settle the issue. These tests are commonly known as paternity and maternity DNA testing (for father and mother respectively). Given the billions of unique people on this planet, the power and precision of genetic testing are amazing.

Reviewed by: Khanh-Van Le-Bucklin, Liat Simkhay Snyder
Last reviewed: April 15, 2009
Dr. Alan Greene

Article written by

Dr. Greene is the founder of (cited by the AMA as “the pioneer physician Web site”), a practicing pediatrician, father of four, & author of Raising Baby Green & Feeding Baby Green. He appears frequently in the media including such venues as the The New York Times, the TODAY Show, Good Morning America, & the Dr. Oz Show.



  • island boy

    Hello, I have a question. Can both parents with type O blood produce a type A+ child? Both my parents are type O and i am type A+. Switches in the hospital can happen to where i am coming from. Please help!

    • Huckle_Cat

      I think he answered this question in the paragraph where he says, “if two parents both have type O blood, all of their children will have type O blood.” That is because they can only pass on a type O gene to their children.

    • Jaclyn Elaine

      My parents are both o+, and me and my twin sister are ab+ so we have been wondering this as well. There is no question of paternity or switching at birth as we are splitting images of our parents, and we are pretty confident in the results of the blood tests

    • nzbule

      found an article with cases that show the rare ways in which this can happen:

    • Cheryl Greene

      Here is more information for you from Dr. Greene — One thing to to consider, your blood type could be an error. Before you go any further, consider having your blood type re-tested.

    • Michelle Patterson

      No. If both of your parents are type 0, they could NOT produce a type A child.
      It is possible that either one of the three of you is incorrect about your blood type. It is still possible they are both your parents if either of the three of you is incorrect about your blood type. Or possibly one of them is not your parent. If you are 100% certain you are type A then you HAD to get that A from one of your biological parents, either your father or mother. Your mother could be type O, but then your father would have to be type A, or vice versa

  • Nean

    my mother has 0 Negative RH blood group – bit of confusion as my fathers dog tags of 1947 simply have 04 blood type…he told me they both have RH O Negative…and his is rare – I am O Positive – born in 1958 in an out back town in the Northern Territory where blood transfusions for the baby be non existent…very confused…my younger brother definitely theirs RH factor child severe anger issues, learning difficulties speech, tactile…I am 55…my parents told me I was adopted they are both in their late 80’s and with cancer I am their carer mum is now in full time care…could you please tell me is it possible for two O negative Rh blood groups to have children…my brother is fine now but was an out of control toddler and child and violent…thanks so much they do not wish to discuss my adoption which is fair enough.

  • Miriam LuvEtte Saucedo

    My parents are both B+ … Why am i A+?

  • Peggy Robinson

    Can A RH Negative And a O Have an A positive child?

  • Peggy Robinson

    Can a RH Negative and A O Have a A positive Child?

  • Miss Jennie

    My dad belongs to B type blood and my mom belongs to O type blood, whereas my brother belongs my dad’s blood type but how come my blood group is A positive?

  • Miranda Decker

    Here’s an odd one. My parents are both o+, so is my sister… I am A negative. So… I’m really starting to wonder how this would be possible….

    • Cheryl Boisoneault

      Same here did you get an answer? my parents are positive to and both my brothers as well None have A blood…Or are they blood type is A negative RH ? I would love to know how this happened

    • Mela

      My parents are both 0 + , me and my brother are 0 – . And its totally fine because 0+parents can only give birth to babies with 0+ or 0 – blood type. In our case it happened to be 0- . :)

    • Charla Satterwhite

      Miranda, did you ever find the answer to your question? Because I need to know the same thing.

  • Mohammed Mubeen

    Hi, i hav a question that my blood group is AB and Rh positive and my wife is O+ and Rh negative so what will be the result for this…?? and if she has O= and Rh positive then what will be the result…??????

  • rj

    hi good eve. i have a question regarding my blood type my parent is A blood type me is B negative is it really my parent

  • Cheryl Boisoneault

    I am RH-A negative . My Mom is O positive and my Dad is B positive …How did this happen?

  • Rose

    I am A-, my sister is A+, my brother is O+………is it possible that we have the same mother and father? There are doubts that we have the same father. We think we have the same mother but our father is the ?

  • Noelito Zipagan Glorial

    pls answer, how about parents with O type, and the child is A??is this possible??pls answer

  • Me Trost

    Question: I am Blood Type O+ and my Brother is Type A+. What Blood Type combination(s) would our parents (RIP) have to of had for me (Sister) to be O+ and Brother to be A+?

  • april

    Hi there,
    Me and my sister are 1yr. and exactly 18 days apart same mom and dad. We have blood type RH O negative and we both have to take the RohGam shot. Now I was told by an RN that it’s impossible for us to be from the same parents and have this blood type. That only one child will come out with RH O negative. Is this true???

  • desteny

    I have a question my sister had her period on novrmber 8 on the 14 she have relationship with one man on december 11 she was in another relation with someone else in january she found out she was pregnant acording to the doctor she consive on december 27 and her due date september 19 she had the baby premature she is A positive the father is Rh o positive and the baby is o positive can that happen

  • Jannette Davidson

    Both my parents are O+, so are all my siblings. I am A+ and my mother swears she never had an affair. I also have very dark skin, no widow peak, and unattached earlobes. Please figure that one out.

    • Cheryl Greene

      Here is more information for you from Dr. Greene –… One thing to to consider, your blood type could be an error. Before you go any further, consider having your blood type re-tested.

      • Jannette Davidson

        I am sure my blood type is correct. I don’t think the U.S. Army, the V.A. hospital and all the times I have donated blood could be wrong. We all know out blood type from getting tested when my grandpa and step dad needed to find a match for kidney disease. From what I gather there is a thing called a genetic mutation, can this be the cause?

        • Cheryl Greene

          I don’t know if it could be genetic mutation. That’s a great question. Does anyone else here know?

  • lorraine wallace

    I am o negative reh both my parents are b+ how is this possibly. ???

  • Stephen Maria Jarrells

    My dad is an O- my mom is an O+ but I am absolutely B- Rh-…does anyone have an answer? My mom refuses to talk & unsure what hospital i was born my dad says he’s my dad and dont mind a blood test. Plz help

  • Heather Hylemon

    I have a question both my parents are o blood type but im a+ an my sister is o as well how is that possible

  • Joanne Jackson

    My mother is B I don’t. Know positve or negative my dad is a postive but I always thought my step dad which is o postive was my dad is it possible?

  • Julie Balfour

    My mum is 0+ I am 0- what blood type could my father be?

    • Kezia Elizabeth

      B, A or O positive or negative

  • jayson

    hi my parents are both os and i’m ab are they my really parents?

    • Marisol Torres

      I am a mom that has O- and my husband has O+, both of the kids that I gave birth to are AB+ Even though teachers have asked our kids if they were adopted, my kids know they were not adopted. So it is possible! I guess rare, but possible ;)

      • jayson

        thank you :)

        • Marisol Torres

          You are welcome!

  • Emma Lane Davis

    i am in my first pregnancy and my blood type is A- and i have Rh- blood yet my mother has A+ and my Dad has O+ and they are both Rh+. my dr tested my blood thats how i know i’m A- and Rh-. but i don’t understand how this is my blood type and my parents are both positive.

  • anne

    helloo,i had a question pls kindly give me an answer .Is it normal that the father ,mother ,and a daughter had same blood types?coz one of my friend family they had all O POSITIVE blood types.

  • Chris

    Please help…. I’m confused,.. My blood type is B positive and my mothers is A negative, is this possible ?

    • Michelle Patterson

      Yes. Your father must have been B positive. Everyone actually has TWO letters (one from each parent) and TWO Rh signs. So since you are B+ you are either BO++ or BO+- (BB++ or BB + – would also be type B+ but that can’t be you, because of your mother she had no B to give you or it would show in her blood type. ) Your mother, being A- is actually either AO– or AA– She could have given you the O. Obviously she didnt give you a B, which is why you are BO not BB.) If she had given you the A you would be type AB. So she gave you the O. She definitely gave you the – since she only has – – . So she gave you O – and your father must have given you B+ which means you are BO+- which would be interpreted as type B+

  • april

    My blood type is B- HR what would my parents blood types be?
    I have 2 kids and they both have AB+, I was given the rhogam shot during and after both my
    prengnecies, why?

  • kat

    Okay, my parents are rh+ both of them. what would i be?

  • Ravi Bhatia

    my son is ab positive , me & my wife are both b positive. is it possible?

  • Jacqueline Gardiner

    I remember talking with ny genetics instructor about this. Both my parents are rh positive. My Dad had issue believing I was his because I’m rh negative. Initially she said no, its not possible for two positives to have a negative. My heart fell through my stomach. As I turned to walk away she yelled “wait a minute!” I learned that one of them carries the recessive gene. Pretty cool stuff.

  • now confused over bloodtyping

    ok, my first husband was O+ and so am I , our child is O-, my second husband is A+, me O+ and our child is A-… how is this?

  • TheOtherRosie

    That sounds simple enough. Parents each have 2 genes that determine the blood type of their offspring. Each parent shares only 1 of their 2 genes with their offspring. The dominate gene determines the offspring’s blood type. I’ve been out of college for a long time. I didn’t have much science in college, but I’m making up for it now. Enjoyed your article very much. Genetics is so very interesting. Thank you for sharing. : )