A child with O blood type parents has O blood type. The law of inheritance of ABO blood type is that the blood type of the parents determines the blood type of the child, and each inherits one blood type gene to the child. When both parents have blood type O, the child will inherit the I-antigen, and the two I-antigens will determine the child’s blood type O. If one parent is O and the other parent is another blood type the child’s blood type will change and may be A, B, O or AB. In addition to ABO blood typing there is also RH blood typing, of which there are two types, one RHD positive and one RHD negative. The blood type of the child can be deduced using the laws of heredity, but there are some errors that require blood typing.