Expert: Walter Hintz - 12/19/2005

Question
A friend mentioned some stuff I'm not completely sure about... that blood types A, B, O and AB have subcategories.

1. Blood type A (subtype AA, AO)
2. Blood type B (subtype BB, BO)
3. Blood type O (subtype OO)
4. Blood type AB (subtype AB)

In essence, he's of the opinion that a couple with blood types A, B, or A and B can have a child with type O blood. Is he correct? Thank you!

Answer
 Hi A.C.
The "subcategories" you mention are,in genetic terms, genotypes. Keep in mind that for every trait we receive a gene from each parent and genotypes tell us what we have.  I am type A. My mother was type O and my father was AB.  I gat an A from him and an O from my mother so my genotype is AO.  A and B dominate over O.  A persom with A or B could have a child with type O if they carry an O and if d their mate does also.  A person with AB cannot.