Question

1. what are the classes of human blood groups based on?

Explanation:

Human blood groups are classified based on the presence or absence of certain antigens on red - blood cells. The two main systems are ABO (A, B, AB, O) and Rh (positive or negative). In the ABO system, the presence of A or B antigens determines the blood type. In the Rh system, the presence or absence of the Rh factor (D antigen) is considered.

Answer:

The presence or absence of specific antigens on red - blood cells, mainly in the ABO and Rh systems.