If the mother has blood type A and the father has blood type O, the child may have blood type A or O. When the mother has blood type A, her blood type gene is AA or AO; when the father has blood type O, his blood type gene is OO. When the mother has blood type A, her blood type gene is AA or AO, and when the father has blood type O, his blood type gene is OO, and their child will receive one blood type gene from each parent to make up his or her own blood type gene, so their child’s blood type gene may be AA, AO, or OO. The blood group gene A is dominantly inherited and the blood group gene O is recessive, so the blood group genes AA and AO behave as blood type A and the blood group gene OO behaves as blood type O. Therefore, when the mother has blood type A and the father has blood type O, the child may have blood type A or O, but the results of the blood type test should be used as the basis.