How does the ABO-A2 phenotype differ from ABO-A1?

The ABO-A2 phenotype is characterized by the expression of a specific type of A antigen that is distinct from the ABO-A1 phenotype. The A1 phenotype typically expresses a greater number of A antigen sites compared to A2. Specifically, A1 expresses about four times as many A antigen sites as A2.

Therefore, the choice stating that the A2 phenotype expresses about one-quarter the A antigen sites compared to A1 accurately reflects this relationship. The differences are due to variations in the glycosylation patterns of the A antigens, where A1 has additional terminal sugar residues that make it more complex and abundant than A2.

Understanding the nuances of these blood group phenotypes is crucial for applications in transfusion medicine and organ transplantation, as the presence or absence of specific antigens can influence compatibility.