Blood Types 101: An Introduction to ABO Blood Types and the Rh System

If both of my parents have O positive blood, is it possible for me to have O negative blood?
Debbie

Blood Types 101: An Introduction to ABO Blood Types and the Rh System

Dr. Greene’s Answer:

Genetics can be so confusing! I can see how the issue may appear murky. Because blood tests are common many people have questions about the genetic information found in the ABO blood group and Rh system.

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 because 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.

ABO Blood Types

First let’s look at the ABO blood types. Each person receives an A, a B, or an 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 with 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.

Rh System

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. Thus 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.

This is why 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.

Non-ABO, Non-Rh Systems

As it turns out, there are more than a dozen complete blood group systems other than the ABO system and the Rh system. This enables us to look at inheritance and family trees with greater precision.

Specific tests are available (through blood banks) to determine whether someone is a child’s parent.

Unless such testing indicates otherwise, there is no reason, based on your blood type, to be concerned that your parents might not really be your parents.

Dr. Alan Greene

Dr. Greene is the founder of DrGreene.com (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.

  1. Flourish

    Good-Day.
    I had abortion at 21yrs without RhoGAM shot, now marriage and discovered that I am RH negative. Married to a RH positive husband. Got pregnant, had brownish red discharge at 9weeks for just a day, wasn’t heavy enough to wet a sanitary pad. Was just told at the hospital to rest well.

    I had preterm labour at exactly 19weeks (contractions of the uterus, back pain) that lasted for a day then the amino fluid bursted and a D and C was done. It was a male fetus, then I received the RhoGAM shot about 48hrs after the miscarriage. Was later told there were retained products and was evacuated after one week of the miscarriage. It’s been 2weeks since the evacuation yet, Lochia is still coming out.

    My question is: could I have been RH Sensitized that led to the miscarriage at 19weeks? What is my probability of getting pregnant with a healthy baby in my next pregnancy, because I read that if one is already Sensitized, RhoGAM would not work.
    Thank You.

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  2. Carla

    If my blood type is B+ and my 3 month old sons is B+ and his father is O+ And his father is disputing paternity how likely is he to be the dad It’s for his dad and his family’s piece of mind as a DNA test ain’t been done yet

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    • Hi Carla,

      If the mother is B+ and the father is O+, there is a 75% chance the baby will be type B and a 93.7% chance the baby will be RH+.

      This doesn’t prove anything except it is a likely outcome. A DNA paternity test is 99.999% accurate and is considered proof of paternity.

      Best,
      @MsGreene

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  3. Michelle

    My blood type is O+ and my son blood type is B+ can the father in anyway possible be A+ .

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    • Michelle,

      If one parent is O+ and the child is B+, the other parent can be B+ or AB+, but not A+.

      The next step is to have everyone’s blood types retested or have DNA paternity testing done. Blood types can not determine paternity, but they can rule it out. DNA paternity testing can determine paternity.

      Hope that helps,
      @MsGreene

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  4. Annie

    Dr. Greene, pls answer my questuon.. I am very confused about the blood type of my Son..the blood type of my son is Type O..how come that is the blood type of my son if my blood type is type B and his father is blood type AB?is their any chances that my Son will inherit the blood type of his grand parents?

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    • Annie,

      Children do not inherit the blood type of their grandparents, but there is a very rare blood type (0.0004% or about 4 per million in the general population) known as the Bombay Blood type. In some places such as Mumbai (which was formerly called Bombay) the occurrences can be as high as 0.01% or 1 in 10,000. This group does not fall into the ABO system and the usual tests for ABO blood show them as group O.

      The Bombay blood type is usually only found in small communities where there are other people with the hh blood type. Both parents have to be h carriers, though a parent can be a carrier without actually having Bombay type blood.

      If you suspect your child may have the Bombay blood type talk to your doctor about a specialized test for this blood type as it does not show up using the normal ABO blood type tests.

      DNA paternity tests are still accurate (99.999%) with type hh blood and are considered the only accurate test for paternity.

      Best,
      @MsGreene
      Note: I answer a lot of questions on DrGreene.com, I am the co-founder of DrGreene.com, Dr. Greene’s business partner and wife, but I am not Dr. Greene, nor am I a doctor. Please keep that in mind when reading my comments and replies.

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  5. Ann

    My late husband was B+, I am A- and years ago was given a rhogram shot after each of my deliveries to protect the next child when I become pregnant again. Can you explain to me again why that was necessary?
    And also what are the blood type possiblities for an A- mother & B+ father?

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  6. Nicole

    Ok Here’s what I know…My husband’s blood type is A+….his father is O+. My blood type is O+, my mother is A+ , her father was O+. I don’t know my fathers he’s dead. What do you believe my father’s type might have been? Also my husband and I have 4 children, all 4 are O+ like me. Is that rare for them all to be O +?

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  7. Shell

    I am B-, the father was – but not sure the letter of his blood type. What are the possibilities for the blood type of the child?

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  8. James

    Father’s blood type is AB+
    Mother’s blood type is O-
    What should the baby’s be?

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  9. Irene Dietrick

    If both parents are O+ and their daughter (me) is A-
    Is this possible ?

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    • Misty

      unfortunately, no you would not be able to get an A blood type from two “O” parents. The genotype (genetic makeup of an organism combination) to an O blood type is two homozygous recessive individuals with the recessive trait of “ii” so ( ii+ii can not equal any other blood types but either O- or O+. There aren’t any dominant A or B blood types in your parents, therefore they are not able to pass it on.

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  10. Dee Gray

    I am B+pos & mother is O+pos (living), what was my fathers blood type? He’s been deceased over 20 yrs & said he had a more rare blood type but I dont know if that was true. I have no way to test this.. Any help is appreciated. Thank you! Dee

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    • If a child is B+ and one parent is O+, the other parent could be B+ or AB+. The rarity of a blood type changes based on ethnicity.

      – Caucasians have a 9% likelihood of having B+ blood and 3% likelihood of having AB+ blood type.
      – African Americans have a 18% likelihood of having B+ blood and 0.3% likelihood of having AB+ blood type.
      – Hispanics have a 9% likelihood of having B+ blood and 0.2% likelihood of having AB+ blood type.
      – Asians have a 25% likelihood of having B+ blood and 0.1% likelihood of having AB+ blood type.

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  11. worry

    I’m opos my klady is bneg and our son is abneg is this possslbe??

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    • While this is not considered a possible outcome, keep in mind there may explanations. It’s not uncommon for one of the three test results to be remembered incorrectly, or recorded incorrectly or even possible that the test results are not correct. I’d recommend re-testing all three blood types as the first step.

      @MsGreene (not MD)
      Executive Producer, DrGreene.com

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  12. heavenly angel

    My husband is 0+ an I am a+,,, an both of our children are o+,,,,is there a chance my children only have his genetics more then mine,,, my daughter was told my husband is not her father but I know he is 100%,, do you have any compelling information that could ease my daughters mind with this. Thank you

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  13. Linda

    Pls. Help me understand… My husbands blood type is B+
    My blood type is O+
    My daughters blood type is O+
    My sons blood type is A+
    I am being told my husband is not the father of my son?
    His can’t be possible. Your input please and thank you
    so very much. Linda

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    • You alone know if there is no chance someone else could be the father of your son. DNA testing would confirm this. The blood types you’ve listed indicate otherwise, but there could be several reasons for this:
      — The tests are wrong. Blood tests results can be in error.
      — The test results were recorded or remembered incorrectly.
      — There was an extremely rare gene mutation.

      Hope this helps!

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  14. Sabrina

    I am rh negative and my partner is a what blood group would my children be. Its impossible to find out my children’s blood group,tried everywhere. I am from Ireland

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    • There is some information missing from your comment. What is your complete blood type? What is your partner’s full blood type?

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  15. anewlife4us

    My parents were both 0 Negative, but my Mothers Parents – one was 0 Negative, the other was 0 Positive. My Mother is 0 Negative, but both her sister and brother are 0 Positive. My brother and my sister are both 0 Negative, but I was never tested, it was just assumed that I was 0 Negative. Could I be something different?

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  16. JM de Guzman

    Is it possible that both parents have B+ blood type and the daughter will be AB? How possible is that or is it really impossible?

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  17. debbie

    If both my parents are O positive is it possible for me to have Rh O negative blood.

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    • Yes, it is possible. There is only a 6.25% chance, but that means that out of every 400 children born to two O+ parents 25 of them will have O- blood type.

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      • RR

        if both parents are o negative is it possible to be born with o positive child??

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        • RR,

          According to our current science, two O- parents can not have an O+ child. It would be wise to have all three of you tested again to make sure these types are correct. It’s not unusual for tests to be in error or for the test results to be recorded in error.

          If these blood types are correct, it’s important to know — a mother with O- blood, who has a child with O+ blood needs to be treated before conceiving any other children. Here is Dr. Greene’s Q&A that discusses this issue –> How To Determine and Manage Rh Incompatibility.

          @MsGreene
          Co-founder & Executive Producer, DrGreene.com

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  18. Deeann

    My daughter just found out that she is B+. My husband, who just past and i have A+ blood. Can this happen? i am a little worried.

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  19. Namrata

    Dear Dr,

    My Blood Group Is A+ and My Husband blood group is O- Please let us know which blood group our children will have? Also please let us know is there a chance of pregnancy.

    Thanks & Regards,

    Namratha Ranya

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  20. Fiona

    If both of my parents are O+, how is it possible to have B+ blood typing. To my limited understandings of basic biology It’s not possible?
    Thanks for your help!

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  21. carol

    My mother was 0 negative, her only sibling was AB negative. Their parents were first cousins, the mother of my mother and the mother of her husband were sisters. I’m trying to figure out what my grandparents blood type has to have been. Is the AB blood only received if one of the parents is AB? Or could one parent be A0 +/- and the other be BB or BA or BO +/- ? Do both of the grandparents have to have an 0 in their blood to produce an 0 negative child?

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  22. Anup Solanki

    If both of my parents are o positive blood, is it possible for to me have B negative blood?
    Please give me your valuable answer..

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