A and B are co-dominant ( which is very unusual) and that is why when an offspring receives an A allele from one parent and the B allele from the other parent that they are AB group as neither is dominant over the other. The rhesus factor is distinct from the ABo system. Being +in the phenotype can mean that your genotype is either ++( pure breeding homozygous dominant) or +-. Which means that you are heterozygous ( different) for your RH. Factor .But you are still + group ,also called rhesus positive ,because the pos. Dominates the neg. ( -) But you are not pure breeding for RH. Plus when you carry the recessive neg. Allele. I am not absolutely sure exactly what you are asking but I hope this information helps.
