Final answer:
Weak agglutination with anti-A typing sera is typically observed in blood group A2 due to its lower amount of A antigen compared to other subtypes like A1.
Step-by-step explanation:
Weak agglutination with anti-A typing sera is to be expected with blood group A2. Blood group A2 is a subtype of type A characterized by a lesser amount of A antigen on the red blood cells compared to the A1 subtype.
This can result in weaker agglutination when tested with anti-A sera, which is designed to react strongly with the A antigen. The A2 group is still part of the ABO blood group system, which includes A, B, AB, and O blood types, and is relevant for blood transfusions and understanding immune responses to blood antigens.