AUGUST 2, 2023

Blood Type Inheritance Chart: What It Can (and Can’t) Tell You About Biological Relationships

A blood type inheritance chart maps out which ABO blood types are possible for a child based on the parents’ blood types. It’s one of the most-searched blood type questions, often from someone who just learned they’re expecting and wants to know what blood their baby will have, or from someone trying to make sense of a family blood type that doesn’t seem to add up. The chart can narrow down the possibilities. It can’t identify a person as a biological parent, and it can’t clear every non-parent, either.

How Blood Type Inheritance Works

Every person carries two ABO gene versions, one inherited from each parent: A, B, or O. The O version stays hidden whenever it’s paired with an A or B version, which is why a parent’s own blood type doesn’t always predict what they can pass down. Rh factor follows a similar hidden-gene setup, with Rh-positive masking Rh-negative. For more on how these inherited patterns connect to ancestry and geography, see our guide to blood type and heritage.

Blood Type Chart: Parents to Child

The blood type chart parents use to predict a child’s possible type lays out every ABO combination: which types two parents can and can’t produce together.The blood type chart parents use to predict a child’s possible type lays out every ABO combination: which types two parents can and can’t produce together.

Source: The Red Cross

A few combinations tend to surprise people. Two parents with type A and type B blood can have a child with any of the four blood types, including AB or O. Two parents who are both type O will always have a type O child, since neither one has an A or B gene to pass down.

‘What Blood Type Will My Baby Have?’

Your baby’s blood type will depend on which gene versions each parent carries. Two parents who are both type A could each be quietly carrying a hidden O gene, which means their child could still turn out to be type O. The chart shows what’s possible, not a guarantee, unless both parents are type O or neither parent carries a hidden recessive gene.

Rh factor follows its own version of the same rule. Two Rh-positive parents can have an Rh-negative child if both happen to carry a hidden Rh-negative gene, the same way two type A parents can end up with a type O child.

How Blood Type Can Rule Out (But Not Confirm) a Biological Relationship

Blood typing has one narrow legal use: ruling out a possible father, not confirming one. If a child is type O, a man with type AB blood cannot be the biological father, since an AB parent can’t pass along the combination needed to produce a type O child. But blood type alone can’t confirm paternity even when it doesn’t rule someone out—too many unrelated people share the same blood type for that.

DNA Testing Is the Only Way to Confirm a Biological Relationship

A legal, court-admissible DNA test examines far more of your genetic code than the ABO and Rh genes alone. That broader analysis is what lets it reach a probability of 99 percent or higher, the threshold considered conclusive for paternity. If you need results that will hold up in a legal proceeding, testing has to go through DDC’s supervised, in-person collection process. A home paternity test runs through the same lab analysis but can’t be submitted for legal purposes.

Frequently Asked Questions

Can two type O parents have a child with a different blood type?

Both parents only have O genes to pass down, so their child will always be type O. It’s one of the few combinations on the chart with just a single possible outcome.

Is Rh factor inherited the same way ABO blood type is?

Yes. Rh-positive is dominant over Rh-negative, the same dominant-and-recessive pattern that governs A, B, and O. That’s why two Rh-positive parents can still have an Rh-negative child if both carry a hidden Rh-negative gene.

Why do siblings sometimes have different blood types?

Each parent can carry two different gene versions and only pass one down to each child. Two parents who are both type A, for example, could each carry a hidden O gene; one child might inherit two A genes and test as type A, while another inherits an O gene from each parent and tests as type O.

Can a person’s blood type change over time?

Under normal circumstances, no. Your blood type is set at conception and stays fixed for life. The rare exception is a bone marrow or stem cell transplant, where a recipient can eventually take on the donor’s blood type as their blood-forming cells are replaced.

Does a child’s blood type have to match one of the parents exactly?

Not always. A child can have a blood type that’s different from both parents, most notably when two type A or two type B parents have a type O child, or when type A and type B parents have a type AB or type O child. The chart accounts for these outcomes; a single parent’s blood type on its own doesn’t.

About DNA Diagnostics Center (DDC)

DNA Diagnostic Center is the world leader in paternity and relationship testing. We serve healthcare professionals, government agencies, and individuals around the world to determine family relationships with trusted accuracy.

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