Why does ab blood have only a and b antigens?

AB blood type has both A and B antigens on the surface of red blood cells because individuals with this blood type inherit one A allele from one parent and one B allele from the other. This combination results in the expression of both antigens, allowing for a unique blood type that lacks the antibodies against either A or B antigens. Consequently, AB blood type can receive blood from any ABO type, making it a universal recipient.