If the father has O blood type and the mother has A blood type, then the child’s blood type could be O or A.
It is generally believed that blood type is divided into four types: A, B, O and AB. If there is only A antigen on the red blood cells, then the blood type is A. If there is only B antigen, then the blood type is B. If both A and B antigens are present, then the blood type is AB, and those who don’t have either of the two types of antigens are type O.
If the father’s blood type is O, it means that there is no A and B antigen on the surface of the father’s red blood cells. If the mother’s blood type is A, it means that there is only A antigen on the surface of the red blood cells, and the child may have O blood type, or the child may be inherited by the mother and have A antigen, and the child may then have A blood type.