Blood type is determined by the combination of three genetic factors, A, B and O. Based on the blood type of the parents, the blood type of the child born later can be determined. The inheritance rule of blood type is: the offspring of blood type A and blood type A can be blood type A, blood type O. The offspring of blood type A and blood type B may have blood type A, blood type B, blood type O, blood type AB. the offspring of blood type A and blood type O can be blood type A, blood type O. the offspring of blood type A and blood type AB can be blood type A, blood type B, blood type AB. the offspring of blood type B and blood type B can be blood type B, blood type O The offspring of blood type B and blood type O can be blood type B, blood type O. The offspring of blood type B and blood type AB can be blood type B, blood type A, blood type AB. The offspring of blood type O and blood type O can only be blood type O. The offspring of blood type O and blood type AB can be blood type A, blood type B. The offspring of blood type AB and blood type AB can only be blood type AB.