A person's genotype would either be BB+ or BO+ if they had blood type B+. The O allele does not create any antigens, whereas the B allele controls whether the B antigen is present on the surface of red blood cells. The presence of the Rh factor, a distinct antigen located on the surface of red blood cells, is indicated by the "+". An individual with blood type B+ would therefore have at least one B allele, one Rh allele, and perhaps another B allele or an O allele.