Can a Child Have Blood Type AB When the Father is O and the Mother is AB?

There is a common question that arises in genetics: if one parent has blood type O and the other parent has blood type AB, can the child inherit blood type AB? This article aims to provide clarity on this topic by understanding the genetics behind blood types and exploring the possible genetic combinations.

Blood Type Genetics

Blood types are determined by the ABO gene, which has three alleles: A, B, and O. The A and B alleles are dominant, while the O allele is recessive. This means that in order to express a certain blood type, an individual must inherit at least one dominant allele, either A, B, or both.

Genotype Combinations

When we analyze the possible blood types of the parents in this scenario, we can determine the potential blood types of their child.

The Father with O Blood Type

The father has blood type O, which means he has the genotype:

OO

Since O is a recessive allele, he can only pass on the O allele to his offspring.

The Mother with AB Blood Type

The mother has blood type AB, which means she has the genotype:

AB

The mother can pass on either the A or B allele to her child.

Possible Genotype Combinations for the Child

When the parents have a child, the possible combinations of alleles for the child are:

AO

This combination results in blood type A.

BO

This combination results in blood type B.

From this analysis, we can conclude that the child cannot have blood type AB. Both possible genetic combinations (AO or BO) contain only one dominant allele (A or B) and one recessive allele (O).

Rare Blood Types and Possible Contaminations

While the main focus is on the genetic combinations, it is important to note that extremely rare blood types such as AB- are possible, but they are extremely uncommon. However, a significant point to consider is the possibility of sample contamination in blood tests.

Sample Contaminations

During the collection of cord blood for neonatal testing, it is possible that the sample can become contaminated with Wharton's jelly. This can lead to an incorrect blood typing result, as Wharton's jelly can cause the red blood cells to clump together (agglutination), which might be misinterpreted as blood type AB. To prevent such misreadings, it is crucial to follow proper sampling and washing techniques to ensure the accuracy of the test results.

Conclusion: While it is not possible for the child of an O father and an AB mother to have an AB blood type based on genetic inheritance, it is important to retest a child if the initial test results seem unusual. This can help in confirming the actual blood type and avoiding any potential misinterpretations due to sample contamination.

Further Reading:

Michael L. Jirka's explanation on blood typing and sample contamination.

Cord Blood testing on gel

Neonatal Hyperbilirubinemia and Direct Antiglobulin Test

By understanding the genetic basis of blood types and the potential for sample contamination, we can better interpret test results and ensure accurate diagnoses and treatments for newborns.