Blood Type Inheritance: Can Type O and Type AB Parents Have a Type O Child?

Yes, a type O child is possible—but the probability is 0%, not 25%. The original article contained a genetic error. Let's clarify the inheritance.

ABO Genetics

• Three alleles: I^A, I^B (codominant), i (recessive).
• Type O genotype: ii (two recessive alleles).
• Type AB genotype: I^AI^B (one A, one B allele).

Punnett Square: Type O (ii) × Type AB (I^AI^B)

	IA (from AB)	IB (from AB)
i (from O)	IAi → Type A	IBi → Type B
i (from O)	IAi → Type A	IBi → Type B

Possible Offspring Blood Types

• Type A (I^Ai): 50%
• Type B (I^Bi): 50%
• Type O (ii): 0% — impossible, because AB parent has no i allele to contribute.
• Type AB (I^AI^B): 0% — O parent has no I^A or I^B allele.

Why the Original Article Was Wrong

It incorrectly listed "OO" as a possible genotype. The O parent contributes i; the AB parent contributes I^A or I^B. No combination yields ii.

Exceptions (Extremely Rare)

• Cis-AB variant: Rare allele encoding both A and B on one chromosome. AB parent could be cis-AB / i → could pass i.
• Chimerism, somatic mutation: Theoretical, not clinically relevant.

Bottom line: Standard genetics: Type O × Type AB → Type A or B children only. Type O child excludes standard AB parentage (consider non-paternity, rare variants, or lab error).