With a mother of blood type O and a father of blood type B, the child may have either blood type O or B. If the mother has blood type O, then her blood group gene should be OO; if the father has blood type B, then his blood group gene should be BB or BO. Since the child’s blood genes come from both the mother and the father, one from each of them, the child’s blood genes may be BB, BO, or OO, and since the B gene is dominant and the O gene is recessive, the blood genes BB and BO are for blood type B, and the blood gene OO is for blood type O. So if the mother has blood type O, then her blood genes should be OO; if the father has blood type B, then his blood genes should be BB or OO; if the mother has blood type B, then his blood genes should be OO. Therefore, if the mother has O blood type and the father has B blood type, the child’s blood type may be B or O. However, the final result of the blood type should be based on the results of the test conducted by professional medical institutions.