Answer by Diane Eager

This combination is possible if the father has a rare condition named Bombay phenotype. This is the lack of a molecule, called H, which connects the A and B molecules to a blood cell’s surface. As a result the blood cells without H do not have A or B molecules on their surface even if the person has the gene for the A or B. Therefore, their blood cells react to a blood group test as if the person’s blood was Group O. However, people with this condition can still pass on the A or B genes to their children. If the children inherit a normal gene for H from their other parent, these children can be A or B blood group, or AB.

In case anyone is wondering, blood groups are no longer used to determine parentage now that we have DNA profiling. Also, Bombay phenotype is a rare condition, but there is a generally available blood test for it.

For more information on blood groups, see the question:
How did A B AB O & Rh blood groups come from Adam & Eve? What blood group were they? Answer here.

Were you helped by this answer?  If so, consider making a donation so we can keep adding more answers.
For USA tax deductible donations click here.
For UK tax deductible donations click here.
For Australia and rest of world click here.






About The Contributor

Diane Eager