The child has type O blood and the combination of the parents’ blood types is O+O,O+A,O+B,A+B. The child’s genetic inheritance is determined by the genetic inheritance of the parents. The gene expression of ABO blood type is negative, and with the combination of two negative genes of the parents, the child’s blood type is still a recessive gene, so the child is type O. As long as both parents do not have AB blood type, A, B, O blood types contain AO, BO, OO genotypes, and when combined with each other, for example, O+O, O+A, O+B, A+B, there is a possibility to form OO such an expression type. This type of expression is O blood type. Therefore, if the parents of a child with type O blood are of the above types of blood, there will not be one parent with type AB blood.