Are The blood proteins A and B codominant?

The genes which determine the ABO phenotype are inherited in a codominant fashion.

ABO blood groups are determined by the presence or absence of terminal sugars on the red cell membrane. These sugars are placed on the red cells by enzymes (glycosyltransferases) that transfer specific sugars to the appropriate carbohydrate chain acceptor. The genes that code for the specific glycosyltranserases are located on chromosome 19. Therefore, the ABO antigens are indirect products of the genes.