ABO Dominant and Recessive Genes

September 10, 2010 at 11:22 am

By Billie Rubin, Hemoglobin’s Catabolic Cousin, reporting from the labs of Stanford Blood Center

Here’s an interesting trivia question: Can a man who is type A and a woman who is type B have a type O baby?

a) Only if the baby is adopted

b) Only if the blood was mistyped

c) Yes

The answer is yes! They have a 25% chance of having a type O baby. We actually have two ABO genes, not one. We inherit one ABO gene from dad and one from mom. In this case, one parent would be AO and the other BO. And each could pass either gene to the baby. You just don’t know they are AO or BO until you do family studies because the O gene is recessive (the blond, blue eyes of the ABO world), and an AO person looks like an A when you type them and a BO person looks like a type B. A type O person would need two recessive genes (OO). Here’s a chart that explains the four possible ABO types of the children: