When a child is ab what blood groups can the parents be? is it possible to be an A and an O ? thanks

Question

the sibling of the child is blood group o, does that make any difference?

Answer 1

O is recessive and if the A or B is present that will be the type.  It is possible to be AO and BO. Parents are AO or AA and BO or BB or AB.

Answer 2

No, an AB child cannot come from parents that are A and O. One parent could have the wrong blood type information, so that should be doublechecked. (For years my dad thought he was the wrong blood type based on an incorrect blood type on his army dog tags---it can happen.)

An AB child can be the product of two AB parents, an AB parent and an A or a B parent, or a B parent and an A parent.

An A parent and an O parent can only produce kids who are A or O.