ABO blood group system gives type O. As both "I" and "I" are dominant over "i", only "ii" people have type O blood. Individuals with "II" or "Ii" have type A blood, and individuals with "II" or "Ii" have type B. "II" people have both phenotypes, because A and B express a special dominance relationship: codominance, which means that type A and B parents can have an AB child. A couple with type A and type B can also have a type O child if they are both heterozygous ("Ii","Ii"). The "cis-AB" phenotype has a single enzyme that creates both A and B antigens.
Irish Blood Transfusion Service Service. The frequency of blood groups in Ireland is as follows: It is important that the IBTS collects enough O Rh D positive blood as almost half the population are that blood type. Donors with O Rh D negative are known as universal donors. Their blood can be transfused to patients of any other blood group in an emergency or if the patient's own blood group is unavailable. Because any patient can receive O Rh D negative blood, the IBTS need to have extra O Rh D negative blood available at all times. The service depends entirely on voluntary donations