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My Blood Group is Different From That of ‘My Kids’.

January 11, 2020

Blood Group

My blood group is different from that of ‘my kids’. Should I be worried about their paternity?

Consider this recent enquiry about blood groups:

Hi Doc, my two children are blood group O+ while I am A+; should I be worried about the paternity of the children? Although my wife is O+ ……

Here’s what we replied:

Understanding Blood Groups

The blood group anyone can have is from the ABO classification.

(The + refers to Rhesus blood type which is another category, but your question relates more to the ABO blood group which we will look at below).

How individuals develop blood group

So the blood group.

If someone has blood group ‘A’ they actually have 2 genes that could make up the group – AA or AO.

Despite the ‘O’ gene’s presence, the person’s class is ‘A’ blood group, because when they occur together, ‘A’ gene is dominant while the ‘O’ gene is not.

So you may have 2 individuals – one with AO genes; another with AA genes who both have the ‘A’ blood group.

(Likewise, someone with B blood group can either have BB genes or BO genes but is known as ‘B’ blood group).

The Blood Group difference and Paternity

So back to the specific issue – when you have A blood group you are either AO or AA genetically.

Now when a person with blood group A (with AA genes) partners a blood group O individual (ie OO genes) they have kids with AO genes.

This means the children will be blood group A (as the ‘O’ is the recessive gene in the AO gene combination).

If the person with blood group AO partners an O, their kids can be AO and OO.

Terminology clarification for blood group

So yes, your kids can have OO (O group) even if you are A group – if your genes are AO, not AA.

To illustrate further, – if you are blood group A with AO genes, while another person is also blood group A  but AA gene.

(This is very possible depending on what we inherit from our parents).

Both of you are called blood group A because whenever A gene and O gene appear together, A is dominant and the AO gene person is said to have blood group A, same as the AA person.


Hope this is not too long (or confusing) an explanation, but if you genuinely feel you have good reason to doubt the paternity of the kids, the best way to address this is with a paternity test rather than blood groups alone.

You can delve deeper into blood groups here and here.

Read about other blood type challenges such as with Sickle Cell disease here.

Have you any questions about blood groups or blood type? Ask or Comment below:

Editing by AskAwayHealth Team


All AskAwayHealth articles are written by practising Medical Practitioners on a wide range of health care conditions to provide evidence-based guidance and to help promote quality health care. The advice in our material is not meant to replace the management of your specific condition by a qualified health care practitioner.
To discuss your condition, please contact a health practitioner or reach us directly through

Image Credits: Canva

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