Understanding Blood Types

Understanding blood types, and the genetics of human blood is far easier than that of any other human tissue.

Human blood genetics are quite complex because at each point there are a number of possible characteristics. Nevertheless, understanding blood types, and the genetics of human blood is far easier than that of any other human tissue. To make things a little easier to understand, here are some guidelines for understanding how both the ABO blood types and the Rh system work.

The ABO Blood Types

  • Each person receives an A, a B, or an O gene from each parent.
  • The A and B genes are co-dominant, and the O gene is recessive.
  • 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.
  • A child with type O blood can have parents with type A, type B, or type O blood, but not type AB. Conversely, if two parents both have type O blood, all their children will have type O blood.

The Rh System

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.
  • 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.
  • Most children who are O negative have parents who are positive, since the +- combination is so much more common than the — combination.
Medical Review on: August 28, 2008
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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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mother A and dad 0 both children are o

Georgia,

That is a very common and expected outcome. There is nothing to worry about.

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 Doctor, I have 0+ blood, my mother is sure she has A+ and my father has AB+. Is this actually possible? Should I look into getting a DNA test?

Hi Kay,

Thanks for writing in.

If your mother has A+ blood and if your father has AB+ all of their children will have A, B or AB type blood. They can not have type O blood. Their children could be Rh+ or Rh-.

Should you look into a DNA test? First, you should confirm all three blood types, then you should consider the value of the information you will get from a DNA test. For many people, the decision becomes clear as they consider the possible outcomes.

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.

Felix is my name from nigeria,my blood group is B+ and my wife is B- and my 3year old son blood group is O+ is this posible sir THANKS.

Hi Felix,

Thanks for your inquiry.

Yes, it is possible for one parent to have B+ blood, one parent to have B- blood and their child to have O+ blood. In fact, the odds are 6.25% that a child of theirs would have type O blood and 75% chance that the child’s blood would be Rh+.

If you would like to know more, 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.

Hello doctor,

My sisters murderer had blood type A positive. I got a call back from the lab. The initial laboratory determined that the initial lab had mistyped the blood of the murderer. The independent lab determined that the blood was from a AB positive person. My question is, can this new result be the same person , since the murderer surface antigen carries A and B?

Could Mother and Father be O and child be A?

Dear Sister,

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

It is common, however, for blood types to be different than they are thought. It is wise to have all your blood retested before coming 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.

Father o+ mom b-, child o-. What’s the odds?

Hi Henry,

It is perfectly normal for one parent to have O+ blood, the other to have B- blood and their child to have O- blood.

If one parent is type O and the other is type B, there is a 25% chance their child will have type O blood. If one parent is Rh+ and the other is Rh- there is a 25% chance the child will have Rh- blood. These two numbers don’t always match, but in this case, they do.

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.

Hello Dr. Greene,

I’m O positive. I have two daughters one is O positive like me and the other is AB Positive.
That means My husband is AB positive as well? or what would his blood type be?
Thank you in advance.

Hi Susie,

If one parent is O+, his or her children cannot be AB+. I suggest you have your blood types retested. It is not uncommon for blood types to be different than they are thought to be.

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 had a paternity test done for my son, and on the results it shows for me under the section of system HLA, A 2,3 and B 7,60. Then another section under HLA Table is says N = 5528. Can you tell me if any of that indicates which haplotype group I would fall in or do I need a different kind of test to show that.

I am RH negative and sensitized (I have anti D antibodies). My husband/son’s father is RH+. Is there a way (blood test maybe) to determine if my husband is dominant or recessive RH+?

Hello,

Hope you are doing well..!!

There is one question which bother me everytime i thought of it, your comments will be meaningfull. I am 25 years old my mother is A negative, my father, elder sister and even younger brother are B positive but when i came across to my birth certificate i found my blood type is written like this A++ is that means double positive ? I never heard of it what it means?

Thanks & Best Regards :)

Dear Sun,

Thanks for writing in.

I’m afraid I can not help you as I’m unfamiliar with that notation. What is your country of birth? You might find your answer by looking at the notations for that country.

Sorry I can’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.

Is it possible for O- and A+ Parents to have an A- child?

Dear K,

Thanks for writing in.

Yes, it is possible for an O- and and A+ parent to have an A- child. This is considered 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.

if mother is O positive and father is A negstive can child be AB negative?

Hi Rob,
Thanks for writing! Our current understanding of genetics is that it is not possible for one parent to be O, the other to be A, and their child to be AB.
It is wise to have all your blood retested. It’s not uncommon for blood types to be different than they are thought.
Hope that helps!
Alexandra (caring helper at drgreene.com, not a doctor)

If I am o negative and my boyfriends is b positive can we have a child together?

Hi Lexi,
Thanks so much for writing in! Great question. Dr Greene answers it here (http://www.drgreene.com/qa-articles/determine-manage-rh-incompatibility/) – basically, for Rh- mothers with Rh+ fathers, an injection of RhoGAM is typically given to help make sure everything goes smoothly.

Hope that helps!
Alexandra (caring helper at drgreene.com, not a doctor)

Im A- and my husband is ab+ our daughter is ab-

im o negative my wife is also o negative.. my child is o Positive is this possible??

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

im o negative my wife is also o negative.. my child is o Positive is this possible??

Hello Dr. Greene

I just want to have some clarification for some questions bothering my mind and your answer will be utmost importance. The questions goes like this 1.) “If my mother and father is both blood type AO or AA, is that possible for me to have a recessive blood type O or should I say it looks like this way AO or just AA? 2.) What if I marry someone with blood type OO, is that possible for me to have a child having blood type OO if we consider that I don’t have the recessive O (e.g. because my parents is both blood type AO or AA, considering that A is dominant than O)?

Hoping for the best answers from you. Thank you and God bless!

Mark,

Blood types are made of two alleles. A, B, and O. Each parent passes one allele to each of their children.

In this scenario, if one parent is AO and the other is AA, their children could receive:
— A from one parent, A from second parent = AA, which is simply called type A blood.
— O from one parent, A from second parent = OA, but because the A is dominant it’s written AO and is simply called type A blood.

Both AO and AA are simply called A.

If someone with AO blood has a child with someone who has type O blood (all O is OO because the O is recessive), their children could receive:
— A from one parent, O from second parent = AO, which is simply called type A blood.
— O from one parent, O from second parent = OO, which is simply called type O blood.

Does this answer your question?
@MsGreene

Hello i have just give birth to a baby girl and her blood group is o negative and my blood group is b positive and my husband’s blood group is ab positive. Will blood incompatibility effect my baby im very concern please help

I thought this is alarming based on my understanding B and AB parent will impossible to produce an O child.

I’m o negative
My son is o negative
What are the chances of his father having a different blood type?? And what are the possibilities of the blood types his dad could be?

If one parent is O- and the child is O-, the other parent could be A-, B- or O-.

Hope that helps,
@MsGreene

i’m a negative and my wife is b positive can we have babies

Of course. Your child could be AB+,O+, AB- or O-. If your wife is a BO+- she would be called B+ because those are the dominate genes. You must be AO– (the only way you could be A-. So your child could be AB–(AB-), AB+- (AB+) or OO+- (O+) or OO–(O-) The possibility of the positive genes come from your wife but your child would definitely get your negative gene. However the + gene is dominate. If the child gets your wife’s negative gene they would be negative for sure. But could get the A and the B or the O from both of you.

I am o positive and my wife is o positive but our baby is B positive why?

I am rh a negative, my husband is o positive. My daughter is ab positive. Is this a possible combination.

I am B+ and my husband is A+ and my son is O- hospital told us this isn’t possible why?

If one parent is B+ and the other is A-, each of their children have a 6.25% chance of having type O blood and a 6.25% chance of having Rh- blood.

For a detailed explanation, see Dr. Greene’s article: Blood Types 102: The Role of A, B, O, and AB Groups In Determining Paternity.

Best,
@MsGreene

The father of my son is blood type B+
I am type O.
My son is A+

We have had 3 DNA tests and all indicate the father is not his father.
I have NO reason to believe this. Please HELP with a reply to my email and here also.
Thank you!

Chimera? Very rare but a possibility! Look it up, it’s kind of hard to explain. Women who are Chimeras have actually been told their children aren’t theirs! They have 2 sets of DNA in their bodies. Check it out and good luck!

Only you, as the mother, know if no one else can possibly be the father. There are extremely rare genetic mutations that result in unlikely blood type combinations, but, my understanding is our current scientific knowledge and testing isn’t able to determine when those rare mutations actually happen. This puts you in a tough spot. My heart goes out to you and your family.

@MsGreene

If my dad is rh neg and my mum is ab neg my sister is o.+me and my other sister are rh o neg.has my sister got same dad as us.

can DNA say 100 percent the biological father of a baby?

DNA paternity tests are exceptionally accurate. If the father is an identical twin, DNA tests won’t be able to tell which man is the father. Also, there are levels of DNA tests. A complete genome (rarely done) is very, very accurate. If you have a paternity test done, the geneticist who provides the results will be able to tell you the accuracy rating of the test they perform.

My mum is o type blood and my dad is b. My brother is b and my sister is o type. I’m a+ can they still be my parents.

I’m O+ and my boyfriend is B-and ours son is O+ is it possible

Yes, this is a possible combination.

I am A RH Positive blood my mum is o+,my sister is 0_ .Can she still be my mum? What should father be?

The short answer is yes. Here’s why:

If the mother has O+ blood and her child has A+ blood the father could have A+ or AB+ blood.

If the mother has O+ blood and her child has O- blood the father could have A, B, or O blood and either Rh+ or Rh- blood.

Dr. Greene explains how this can happen in Blood Types 101: An Introduction to ABO Blood Types and the Rh System

I’m o positive and my husbands A positive … My child is o positive can this be right :/

Your child has a 75% chance of having A type blood and a 25% chance of having O type blood. In addition, your child has a 93.75% chance of having Rh+ blood, so yes, this can be right.

Both my parents are a positive and my brothers are a positive but I’m o negative is this possible?

Hello I have 2 brothers and 2 Sisters they are all A+ and I am the only one who is B+ is it possible for us to have the same biological father?

Yes. There are at least two scenarios that immediately come to mind that would account for that. You could have one parent with type O and the other with type AB, or one parent with type A and one parent with type B.