Are they really my parents?

Question

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 about your parents 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.

Last medical review on: April 15, 2009
About the Author
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Dr. Greene is a practicing physician, author, national and international TEDx speaker, and global health advocate. He is a graduate of Princeton University and University of California San Francisco.
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Recent Comments

Is it possible for parent of O+ have a child of B+

Hello Nyanjo,

Yes, it is possible for a parent to have O+ blood and have a child with B+ blood IF the other parent has B+, B-, AB+, or AB- blood.

I hope that helps.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

Hi,
My blood type is O- and my brothers blood type is A+. I want to know if we have the same father. I don’t know what his blood type is and because we are estranged, he will not tell me. How can I figure out his blood type and if he is my father or my brothers father? The obvious answer is to get a paternity test but he is unwilling. Can you shed some light?

Jojo,

Great question. It is certainly possible for two people to be full brothers if their parents have the right combination of blood types. Do you know your mother’s blood type? If not, let’s assume she is type O+. That’s the most common blood type. If she does, your father would have to be type A+ or type A-. But that is not the only possibility. For instance, both parents could have type A+ blood and still have one child with type O- blood. Wild, right?

There are also a few combinations of parents that would NOT work. For instance, if both parents had Rh- blood, they could not have a child with Rh+ blood. Or if both parents’ blood type was B, they could not have a child with type A blood. Or if either parent had type AB blood they could not have a child with type O blood.

Blood types are only good for very broad grouping. You are right that a paternity test is the only way to know for sure.

I hope you find a way to reconcile with your father, not only so you can resolve this question, but so you can both find comfort and peace.

Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

Explanation not clear and as I understand there are contradictions.
Since Rh- see that the blood of Rh+ is an enemy, how a parent with ++ or +- can have a child with Rh-?
since A or B are dominant, how a child of type O, can has parent of type A or B if both are AA or BB?

The worst if these two conditions are realized. A+,A+ how to get O- ?

“This means that if both parents have Rh+ blood with the +- genes, they could have children who are ++, +-, or –. ”
Or please explain the difference between Rh and the gene +, –

Hi Elias,

I’m so sorry this is unclear.

The Rh system is completely different from the ABO system. Let’s discuss them separately.

If someone is Rh+ it means they have the D Antigen in their blood. The D Antigen may or may not be passed to their children. If they don’t have the D Antigen in their blood they are Rh- and can not pass the D Antigen on to their children. The issues you cite above (“Since Rh- see that the blood of Rh+ is an enemy, how a parent with ++ or +- can have a child with Rh-?”) doesn’t apply since the blood is not ++ or +-. It’s either + or -. For more explanation on Rh- incompatibility, see Dr. Greene’s article How to Determine and Manage Rh Incompatibility.

If both parents were Rh+ they could have children with Rh+ or Rh- blood. If one parent was Rh+ and the other was Rh- they could have children with Rh+ or Rh- blood. But if both parents are Rh- they can only have children with Rh- blood.

Regarding type A, B, and O — A person with type A blood could be AA or AO and a person with type B blood could be BB or BO. Thus if one parent was type A and the other type B they could have children that had type A, B, AB or O blood.

Please let me know if you have further questions.

Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

I am O positive and my child’s father is also O positive (he swears by this , got tested in high school through Red Cross ) my baby is A+ and had jaundice how is this possible ? Does this mean he wouldn’t be the father ?

Hi Kathy,

I hope you are doing well and not too stressed. Our current understanding of genetics is that it is not possible for both parents to have O+ blood, and their to have A+ blood. It’s not uncommon for blood types to be different than they are thought. It is wise to have all your blood retested.

If there is a question about who the father is, a DNA paternity test is the only test considered definitive. They are fairly inexpensive, can be ordered online, taken in the privacy of your own home, mailed in, and results received by mail. They are considered 99.999% accurate.

I hope that helps.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

Dr. Greene,
Is it possible for a parent (father) to produce 1 child with O- and 1 with A+? (different moms). No idea what dad or mom(s) types are.

Hi Steve,

Great question. Yes, it is possible for one parent to have one child with O- blood type and another child with A+ blood type.

  • For the child with type O- blood, both parents could have type A+, A-, B+, B-, O, or O- blood but could not have type AB+ or AB-.
  • For the type A+ child, one of the two parents must have type A blood and one of the two parents must be positive (+) or they can both be + for the D antigen. It could be either parent.

Examples that work:

  • Parent 1 has Type B- blood, Parent 2 has type A+ blood
  • Parent 1 has Type A+ blood, Parent 2 has type A+ blood
  • Parent 1 has Type A- blood, Parent 2 has type O+

If you’d like an explanation of how this works, let me know.

I hope that helps.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

My father is A positive, my mother is B negative and my two sisters and I are all O positive. How is this possible?

Hi Kathryn,

Thanks for writing in.

It is possible for one parent to have A+ blood and the other parent to have B- blood and for their children to have O+ blood.

Blood types are comprised of two alleles for the “letter type”. Each person gets one letter allele from each parent. The most common letters (by far) are A, B, and O. It would be much clearer if our naming convention was more clear, but both type A and type B can have an O allele. Here is what that looks like:

  • Type A = AA or AO
  • Type B = BB or BO
  • Type O = OO
  • ype AB = AB

Additionally, if either parent is Rh+, their child can be Rh+ or Rh-. It is only if both parents are Rh- that their children can only be Rh-.

If your father has type A+ blood and if your mother has type B- blood, your sisters could have gotten an O allele from each parent and the D antigen (Rh+) from your father.

I hope that helps.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

If Father is A negative and son is O negative what would the Mother be?

Hi Judith,

Thanks for writing in.

If the father is A- and if the son is O-, the mother could be O+, O-, A+, A-, B+ or B-. She could not be AB+ or AB-. If you’d like to know why, let me know.

I hope that helps.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

When I was born my mom never tested my blood type and she doesn’t want anything to do with me cause once I found out what my blood type was she pushes me away cause I’m not the same blood type like her other 4 kids. I am the only child with one blood type when 4 of my biological siblings are 2 blood types my Brother and 3 sisters are AB+ Blood and I’m not I am only A+ Blood so does that mean they might not be my siblings and she may not be my birth mother. Everyone in her family says I look nothing like my birth mom so I was wondering if I should take a DNA test on Ancestry

Hi Ashley,

I can tell you are very concerned. Let me try to help.

Blood types are comprised of two alleles — one from each parent. If your siblings have AB+ blood, they got an A allele from one parent and a B from the other, but that does NOT mean it would be impossible for you to have type A blood and still be full siblings.

What we call type A blood is either an A allele from each parent (AA) or an A from one parent and an O from the other (AO). Both these combinations are called type A blood.

Here are two scenarios that would work:

  1. One parent is A the other is B, but the B parent is BO. The child get an A allele from one and an O from the other and has type A blood.
  2. One parent is AB and the other is A. The child gets an A from both parents and has type A blood.

Let me know if you’d like more clarification.

I hope that helps.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

If both my parents and myself have rh + blood, does that mean that I am ++ and would definitely have an rh + child? Or is it still possible that I received a recessive rh – gene from my parents and therefore could still have an rh- child?

Hi Stephanie,

If a parent is Rh+ it means they are positive for the D Antigen. The parent may or may not pass that down to their children. If a parent is Rh-, it means they do not have the D Antigen and can not pass it down. Two Rh- parents can not have an Rh+ child, but two Rh+ parents can have children who are either Rh+ or Rh-.

I hope that helps.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

Hi.. Can you please answer my question. The father blood type is AB and the mother is B. Can the daughter has O+ ? Thanks.

Dear Nur,

Thank you for writing in.

If one parent has type AB blood and the other parent as type B blood, they can not have a child with type O blood. However, it’s not uncommon for blood types to be different than they are thought. It is wise to have all your blood retested before jumping to any conclusions.

I hope that helps.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

Hi, If mum is O+ and dad is O- then can the baby be A+?

Hi Paul,

Thanks for writing in.

If one parent has type O+ blood and the other parent has type O- blood, they can have children with type O+ or O- blood, but they cannot have children with A+ blood. However, it’s not uncommon for blood types to be different than they are thought. It is wise to have all your blood retested before jumping to any conclusions.

I hope that helps.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

Sir I have one case to handle,

The Father is O+ and mother is O+
but thier son is B+.

Can this be possible ??

Hi Alan,

If both parents are O+ their children could be O+ pr O-, but they could not be B+.

It’s not uncommon for blood types to be different than they are thought — perhaps one of the parent’s or the child. It is wise to have all your blood retested before drawing any conclusions.

I hope that helps.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

Mum has A+ and Dad B+ can the daughter have AB+?

Hi Laritha,

Thanks for writing in and what a great question. The answer is YES! If mum is A+ and if Dad is B+, their child can have AB+ blood. If you’d like to know how that works, please let me know and I’ll be happy to explain.

I hope that helps.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

A couple with a newborn baby is troubled that the child does not resemble either of them. Suspecting that a mix-up occurred at the hospital, they check the blood type of the infant. It is type O. Because the father is type A and the mother is type B, they conclude that a mix-up must have occurred. Are they correct? Prove your answer.

Hi Kristine,

Thanks for writing in.

It IS POSSIBLE for one parent to have type A blood, the other to have type B blood and their child to have type O blood. Here’s why:

Blood types are comprised of two alleles. The most common (by far) are A, B, and O.
— If a person has type A blood he or she has at least one A allele. He or she can have two A alleles (AA) but can also have one A and one O (AO). Both are called type A blood.
— If a person has type B blood he or she has at least one B allele. He or she can have two B alleles (BB) but can also have one B and one O (BO). Both are called type B blood.
— If a person has type O blood, both alleles are O (OO).

In the example you gave the child could have gotten an O allele from each parent so would have type O blood.

If there is still a question, a DNA paternity test is the only test considered definitive. They are fairly inexpensive, can be ordered online, taken in the privacy of your own home, mailed in, and results received by mail. They are considered 99.999% accurate.

I hope that helps.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

I have A positive blood, my mom is Rh negative and my dad’s is O positive, is this possible

Hi Cheryl,

Thanks for writing in.

If you have A+ blood and if your dad has O+ blood, your mom could have A+, A-, AB+ or AB- blood. Does that answer your question?

Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

I’m AB- and both my parents are O+. I honestly didn’t think it was possible and people always tease me because I look nothing like them at all. my uncle was there when I was born so I know I’m not adopted either.

Hi Jane,

Thanks for writing in.

If you have AB- blood you have to get an A allele from one parent and a B allele from the other. People with type O blood ONLY have O alleles. That is why it is considered impossible for two parents with type O blood to have a child with AB blood.

It’s not uncommon for blood types to be different than they are thought. As a next step, it is wise to have all your blood retested.

I hope that helps.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

Mother is A+. Father is A+. Can daughter be AB-

Hi Miriam,

Thanks for writing in.

Each parent passes one allele down to their child and those two (one from mom and one from dad) make up the baby’s blood type.

If a person has type A blood he or she has:

  1. one or two A alleles and
  2. can have one A allele and one O allele but
  3. can not have a B allele

A person with AB blood has one A and one B allele.

This means two parents with A+ blood can not have a child with AB blood.

It’s not uncommon for blood types to be different than they are thought. It is wise to have all your blood retested before jumping to any conclusions.

I hope that helps.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

My father B+ and Mother is also O+ (Both deceased).. Can they give birth to O negative child as firtlst born

Hi Edward,

Yes, it is possible for one parent to have B+ blood, the other to have O+ blood, and any of their children to have O- blood.

Blood types are comprised of two alleles. The most common (by far) are A, B, and O.
— If a person has type B blood he or she has at least one B allele. He or she can have two B alleles (BB) but can also have one B and one O (BO). Both are called type B blood.
— If a person has type O blood he or she has two O alleles (OO).

Rh+ means a person is positive for the D antigen. Rh- means a person does not have the D antigen.
— If a person is Rh+, he or she can have a child that is Rh+ or Rh-.
— If a person is Rh-, he or she can only have a child that is Rh+ if the other parent is Rh+.
— Two parents with Rh- blood can not have a child with Rh+ blood.
— Two parents with Rh+ blood can have children with Rh+ or Rh- blood.

What all this means is if your father had B+ blood and if your mother had O+ blood they could have a child who is O- and that would be perfectly normal.

I hope that helps.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

Hi,

Here I am Mahi

My mom is AB positive and My dad is B positive and I am A1 positive. How could it be possible?

Can you tell how it could be possible

Hi Mahi,

Thanks for writing in.

If your mom is AB positive and if your dad is B positive, they could have a child that is A positive. A1 is a subtype of A. roughly 80% of people with type A blood are A1.

Blood types are comprised of two alleles. The most common (by far) are A, B, and O.
— If a person has type AB blood he or she has one A allele and one B allele.
— If a person has type B blood he or she has at least one B allele. He or she can have two B alleles (BB) but can also have one B and one O (BO). Both are called type B blood.
— If a person has type A blood he or she has at least one A allele, but the other could be an O allele.
— Rh+ means a person is positive for the D antigen.

In the example you layout, if your mom has AB+ blood and if your dad has type B+ blood, you could have gotten an A from your mother and an O from your father. Your blood type would then be called type A. You could have gotten the D antigen (Rh+) from either parent.

I hope that helps.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

Hi, my husband and me are both RH0 -. And I do believe my both kids were 0 – as well. I remember they were 0 for sure, when they took bloods through the heel prick when babies, but cannot find the paper. I always thought they were 0 – like us, but my sister is telling me that they should be 0 + (not sure why)… could I be right and what I remember is correct?

Hi Martina,

Thanks for writing in.

If two parents have type O blood and are RH-, they can only have children with type O, Rh- blood.

None of our memories are completely accurate, so if blood types are important (such as needing a blood transfusion), they should always be rechecked.

I hope that helps.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

Thanks for the explanation of Rh + and Rh- and how we inherit it. I am one of four siblings all of whom are Rh- while both of our parents were Rh+. I knew that they both had to have what I was taught to call a recessive Rh- gene but thought it was numerically impossible for all 4 of us to be negative.

So glad to help!

@MsGreene

So glad to help!

@MsGreene

So my mother is 0+ my father is O- I am B+ how everyone is telling me my father isn’t my dad but he is saying I am his child I am 34 years old and going crazy I have a younger sister who is O- and a brother who is O+ I am the only child that is B+ please help me

Hi Danna,

Thanks for writing in.

If two parents are O+, they can not have a child that is B+. So either one of your blood types is different than you think (this is often the case) or one of your parents is not your parent. Since your father is already talking about this with you, likely the easiest thing to do would be to tell him you are going crazy and you really want to know for sure. The only way to do that is for both of you to take a paternity test.

DNA Paternity tests can be done at home and are very private. You can order them online and do the whole process by mail.

I hope that helps.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

I found out when my mom was very sick that she had A positive blood. I have A positive but my biological father, which I’ve never had anything to do with. I’m going to be meeting for the second time ever so, of course there’s some hesitation on both sides. Is he or isn’t he’s my father by blood with what I do know about my mom and my blood type? What kind of blood type which he have? Sincerely desperately need to know.

Hi Kelly,

Thanks for writing in and sharing your concerns.

If your mother has A+ blood type, and if you have A+ blood type, your biological father could have A+, A-, B+, B-, O+, O-, AB+ or AB-. In other words, If your mother has A+ blood type and if you have A+ blood type, your biological father can NOT be determined by blood type. He could have any blood type. Why? How can this be? If you want to know the full reason behind this, write back and I’ll explain.

I hope that helps.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

IF.my dad.s blood group was AB.and my blood group is A rhesus positive why was my twin brother.s blood group O.
Thanks

Hi Muriel,

Thanks for writing in and sharing your concerns.

An AB parent can not have a child with type O blood. In your situation, I would try to have all your blood re-tested. Likely one of the blood types is not what you think it is. This is so common that blood types are tested before medical procedures that might require a blood transfusion even when a person is sure they know their blood type.

I hope that helps.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

Hi.
I just want to ask if there could be some cases of having an A+ child while both parents are type O??

Hi Irish,

Our current understanding of genetics is that it is not possible for two parents with type O blood to have a child with type A blood. Two type O parents can only have children with type O blood. But …

It’s not uncommon for blood types to be different than they are thought. It is wise to have all your blood retested.

I hope that helps.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

Hi.

One of my parents is A- and the other is O-. Imagine my surprise to recently learn that I am O+. When I spoke to my parents about the results of my recent test, they agreed it was the same blood type the hospital shared with them when I was born.

Is it possible for both of my parents to be my true biological parents?

Thanks for your time.

Hi Charity,

Thanks for writing in. If one parent has type A blood and if the other has type O blood, they could have a child with type O blood. But if both parents are Rh- they can not have a child with Rh+ blood.

It’s not uncommon for blood types to be different than they are thought. It is wise to have all your blood retested before making any assumptions.

I hope that helps.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

Hi,

Could you help me? just to make my mind clear.
i have a daughter which is AB+ and my blood type is B+…
i had an affair with other guys during that time.

Now, i had read on the internet that B+ and O+ is an impossible match for a AB+ child, the other guy is O+. i didn;t know the blood type of the other guy yet.

does b+ and o+ is impossible to have an ab+ offspring?

Thanks

ChinChan

Hi Joy,

Thanks for writing in.

If your blood type is B+ and if your daughter’s blood type is AB+, her father would have to have type A+, A-, AB+ or AB-.

Blood types alone can not be used to determine paternity, but some times blood type can be used to rule out a possible parent. You are correct that a child with AB+ blood can not have a parent with O+ blood.

If you are concerned about who the father is, the best test is a DNA paternity test.

I hope that helps.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

I am A positive and my ex-husband has rh positive blood.
I had an affair with a man who is O positive.
My daughter is A negative.
Which one is likely to be the father.

Dear KE,

Thanks for writing in.

Sometimes you can eliminate a potential father, based on blood type, but it is impossible to determine paternity from blood type. If you have A-positive blood, and if your ex-husband has Rh-positive blood, and if the man you had an affair with has O-positive blood and if your daughter has A-negative blood, either man could be the father. The information you have does NOT eliminate either man.

A DNA paternity test is the only test considered definitive. They are fairly inexpensive, can be ordered online, taken in the privacy of your own home, mailed in, and results received by mail. They are considered 99.999% accurate.

I hope that helps.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

My husband and I both have A Negative blood types. Does that mean our children also have A Negative blood? My child of 29 years has multiple health problems. Could this be the reason?

Hi Janie,

If a person is Rh negative it means they do not have the D antigen in their blood. If both parents are Rh-negative, their children will also be Rh-negative. If one or both parents are Rh-positive, their children can be either Rh-negative or Rh-positive.

This could not be a reason your son has multiple health problems. The only time this is an issue is if the mother is Rh-negative and the father is Rh-positive and the mother does not get medical treatment for following her first pregnancy.

I hope that helps.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

Me and my wife are A+. Our first born is A+ but our 2nd child is O+. Is that possible? Thank you

Hi Lorenzo,

Yes! This is possible. In fact if two parents have type A+ blood, there is a 93.75% chance each of their children will be Rh+, a 93.75% chance each child will have type A blood, and a 6.25% chance each child will have type O blood.

I hope that helps.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

my dad is AB negative and my mom is O positive and my blood group is A positive are they my parents

Hi Hana,

Blood types can not determine if two people are your parents or not, but in some instances, they can determine that two people aren’t your parents. In other words, there are a lot of people with the same combination of blood types, so blood types can only say “this combination is a possibility or is not a possibility”.

In the situation you describe, if your dad has AB- blood and if your mom has O+ blood, and if you have A+ blood, they could be your parents.

Each parent gets one allele from each parent. In this example, the child got an A from the father and an O from the mother and would have AO blood type. We call that type A blood. If either parent is Rh+ and passes that down to their child, the child’s blood is Rh+.

If you still have questions about paternity, DNA testing will provide the answers. Blood typing will not.

I hope that helps.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

I’m curious on do the dad and child suppose to have the same blood type . I’m O+ he’s O- and my child is O-

Hi Ni’Julum,

Each child gets half the code for their blood type from each parent. In some cases that means the child has a different blood type than either parent because it’s a combination of the two.

If one parent has O+ blood and the other has O- blood, their children can be either O+ or O-. Both are completely normal.

Please let me know if you’d like a more indepth answer.

I hope that helps.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

I’m curious after reading this thread. I am O+ but both of my parents aren’t. I have 3 siblings and I’m the only one that’s O+
I have health issues and I’m starting to feel freaked out. Hopefully I can get some answers. Thank you.

Hi Danielle,

I doubt there’s a reason to freak out. If you are O+, your parents could be O+, O-, A+, A-, B+ or B-. The only blood type that neither one of them could have is AB+ or AB-.

If you’d like to know more about why that is, let me know.

Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

My dad was o positive my mom is o negative with rh negative. I am A negative with rh negative. Is this possible?

Hi Dana,

Thanks for writing in.

Our current understanding of genetics is that it is not possible for two parents with type O blood to have a child with type A blood. However, it’s not uncommon for blood types to be different than they are thought. It is wise to have all your blood retested.

If you want further explanation, please let me know.

I hope that helps.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

Hi
I am B negative – RH negative. My mother is B Positive and my father was AB Positive. How am I RH Negative if both my parents were Positive?

Hi Sandya,

This can be very confusing, but just because both parents are Rh-positive, they don’t necessarily pass it down to their children, in fact, there is a 6.25% chance that each of their children will be Rh-negative.

If you have further questions, don’t hesitate to ask.

Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

Hi I’m blood type B+ and so are my two younger siblings however my father is blood type A+ and my mother is blood type O+ is this possible?

Hi Joshua,

Thanks for writing in.

Our current understanding of genetics is that it is not possible for one parent to have type A+ blood, the other parent to have type O+ blood and their child to have type B+ blood. Parents with these two blood types could have children with blood types: O+, O-, A+ or A-.

It’s not uncommon for blood types to be different than they are thought. It is wise to have all your blood retested.

I hope that helps.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

Hi, Is it possible for me to have O+ blood if my Mom is B+ and my Dad is O+?

Hi Jadon,

YES! This is a very normal outcome.

I hope that helps.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

Hi my blood type is 0 neg and my sister is A pos , my father is 0 neg, not 100% sure about my mother (deceased) but I think she was o neg as well , is it possible that my sister could be my fathers daughter or due to her blood type would her father be different

Hi, I’m so confused in how to know my mother’s blood type and my biological father’s blood type, my half brother’s blood type is RH positive and mine is O positive, and I don’t know what my half brother’s father’s blood was either

Hi Karen,

Every child gets one allele for blood type from each parent. It doesn’t matter which parent provides which allele.

If your father has type O- blood, he’s not ruled out as the father of a child with A+ blood — if the child’s mother had type A+ or AB+ blood.

If the mother had type O-, then she could not have a child with A+ blood — unless the father had type A+ or AB+ blood.

Since you don’t know your mother’s blood type for sure, you can’t make any conclusive determination about your or your sister’s parentage.

I hope that helps.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

My mom is A-, my dad is O+. I’m also A- like my mom, but my sister is AB+. When I was studying blood types, it stood out to me that my sister’s blood type compatibility didn’t match the chart I was looking at.

It’s to my understanding that AB+ blood with A- and O+ parents isn’t even supposed to be possible. I confronted my mother years ago about it and got no clear answers. She was angry with me for questioning it and told me to drop it.

Another odd thing: My mom has blue eyes, my dad has green eyes. I have blue eyes like my mother. My sister has dark brown eyes. So, there’s the seemingly impossible bloodtype combo and nearly impossible eye color combo.

I seriously don’t think we have the same father. I think we’ve been lied to. I stopped questioning our mother because she refused to discuss it. I will always think it’s suspicious though. What are your thoughts? Could it be possible for her to be AB+ and have A- and O+ parents…even a small chance?

Hi Janie,

Our current understanding of genetics is that it is not possible for one parent to be A-, the other parent to be O+ and their child to be AB+. If your parents do have A- blood and O+ blood, they could have children have O+, O- A+ or A- blood.

It’s not uncommon for blood types to be different than they are thought, but your mother’s attitude likely makes this impossible.

I hope that helps.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

I’m a RH negative mom and my husband is AB negative. Our child is O positive. We went to the blood bank and asked them what blood type are child would be. They said that the blood type could be O AB A B negative but it could also be O AB A B positive. Now this was 40 years ago. They said this is because they are rare blood Types.

My father is o positive and my mother is AB negative and me and my sister both are 0 positive to my understanding I should be neither A or B and there is no chance I can be o positive

Hi Carolyn,

Forty years is a long time. Perhaps the blood bank then didn’t know as much as we know now, or perhaps your memory of what they said is a bit foggy.

Here is our current understanding:

  • A parent with AB- blood can only have children that have type A or B or AB blood, depending on the blood type of the other parent.
  • Two Rh- parents can’t have a child with Rh+ blood
  • Type AB blood is the rarest type
  • The only combination of parents that could result in any possible outcome (O+, O-, A+, A-, B+, B-, AB+, AB-) is one parent with type A blood and the other with type B blood and at least one parent that is Rh+, but the other could be Rh+ or -.

If you are still curious, you’ll need to have new blood type tests for the three of you.

I hope that helps.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

Very nice one
I love that

plz give me the answer,if parents both are Rh positive,then their child will be?

Hello,

If both parents are Rh+ their children can be Rh+ or Rh-. If one parent is Rh+ and the other is Rh-, their children can be Rh+ or Rh-. But if both parents are Rh-, their children can only be Rh-.

I hope that helps.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

Hi can you help me sir. My mother and my father is same type o. And my brother and sister is type o. But only me is type b+.

Nika,

Our current understanding of genetics is that it is not possible for two parents with type O blood to have a child with type B blood.

It’s not uncommon for blood types to be different than they are thought. It is wise to have all your blood retested.

I hope that helps.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

My sister-in-law is has AB blood, her mother is O+ and her father is O-. Both her siblings have O blood. How does she have AB?

If I am B- my sister is AB- and my other sister is O- our mother is A- what is my father’s blood type?

Hi Amy,

From all the science and testing we have now, it is believed that two parents with type O blood, can not have a child with type AB blood. There is no reason to think that science is in question.

I hope that helps.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

My mother is A- I’m O positive, my brother is O- what is our fathers blood type ?

Hi Jackie,

If your mother’s blood type is A- and if you are O+ and your brother is O-, and if you have the same father, he could have A+, B+ or O+ blood.

Please let me know if you’d like an explanation.

Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

Hello,

I am O+, my Mother is B- and my Father is A+. My Mother says it is impossible for me to have O+ blood and I should get re tested is this correct ?
Thank you

Hi Christy,

Thanks for writing in with your question.

If your mother has B- blood and your father has A+ blood there is a 6.25% each of their children will have type O blood and a 75% chance each child will be Rh+.

If you’d like an explanation of why that is, let me know.

Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

Hello…

I keep reading everything that you have written on this page and in the comments, and I guess I just need to hear it again? I am B+ and both of my parents are O+. Both of my parents have had cancer and extensive blood work, and I have had my blood work done numerous times. Does this really mean my father isn’t my genetic father? I am scared to get a genetic test… but I can’t stop thinking about it… He never liked me as much as my brother, but my mom told me he was and if he wasn’t, she took it with her when she passed.

Hi HR,

You are right, as far as we know, two parents with type O blood can’t have a child with type B blood. There are extremely rare cases, that I doubt fit your circumstances, where a person with reported type O blood actually has type hh (Bombay). Our test results can’t differentiate between OO and hh, so they are read as O. BUT this wouldn’t result in type B blood in the child. Might there be some other wild anomaly? Something that is ahead of our blood typing technology? If so, that should show up on DNA testing.

Here’s the thing — if your mother is no longer living, you can’t ask her. That means to get any more clarification you would need to talk to your father and perhaps even do a DNA test. What will it do to your relationship with your father if he finds out for the first time that you are not his child? Or maybe he knows and just talking about it will help you both? I don’t know if there’s a way to predict the outcome. It may come down to figuring out what you can live with and what you can not.

Sorry I couldn’t be more helpful.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

if the mother blood is o positive.and father blood is o negative then what will be the blood of children

Hi Kailash,

Thanks for writing in.

If one parent is O+ and the other is O-, all their children will have type O blood.

If they had 100 children (which no two people will have) 75 would have O+ blood type and 25 would have O- blood. If they have two children, it would be perfectly normal for them to be either O+ or O-. The averages only apply over large groups.

I hope that’s helpful.

Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

Hi, I’ve donated blood in the past and it came to me as a surprise that I’m O+, but both of my parents are O-. It that even possible?

Hi Gavin,

Thanks for your question.

Our current understanding of genetics is that it is not possible for two Rh- parents to have a child with Rh+ blood. The Rh+ means the blood is positive for the D Antigen. If neither parent is positive, they can’t pass it along to their children.

However, it’s not uncommon for blood types to be different than they are thought. It is wise to have all your blood retested before jumping to conclusions.

I hope that helps.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

If a mother is A+ and a Father is A+, how likely is it they will have two children who are O+? My parents have always told us they are A+. My sister recently got typed as part of a pre nursing health class. Her type came out as O+. I was curious so I ordered an at home blood test (Eldon Home Kit HKA 2511-1) and the test shows I am O+.

Hi Elixabeth,

If both parents have A+ blood, the likelihood that each of their children will have type O blood is 6.25%. (That means if they had 400 children, 25 of them would have type O blood.)

The likelihood that each child will be RH+ is 93.75%.

Like tossing coins to see how many heads and how many tails, the number averages out after a lot of throws, but the first few may all be the same.

In other words, there’s not reason so suspect two A+ parents aren’t the parents of two O+ kids.

I hope that helps.
Best, @MsGreene
Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.