ABO Blood Group

Table A2. ABO blood group

Blood Group (Frequency in Caucasoids^*)	Genotype	Antigens Formed	Antibodies Formed	Clumping With	Blood Type Acceptable for Transfusion
O (0.45)	i^Oi^O	neither	anti-A	A,B	O
			anti-B	AB
A (0.44)	i^Ai^A or i^Ai^O	A	anti-B	B,AB	A,O
B (0.08)	i^Bi^B	B	anti-A	A,AB	B,O
	i^Bi^O
AB (0.03)	i^Ai^B	A,B	neither	neither	A,B,O

*The frequency of these alleles varies in different populations. For the calculation of frequencies, see gene frequencies. Actually, the A type exists in A₁ A₂ forms; in about 1–2% of the A₂ and 25% of the A₂B individuals, anti-A₁ antigens occur.