So there are three different types of alleles. For the blood group traits, we have allele given by uppercase I with the A SuperScript. We have allele that is given by uppercase I with the B SuperScript, or we have lowercase I. Now, what this means is at this particular locus on the chromosome, we have a specific sequence of nucleotides that codes for a special protein we're going to call protein A. And protein A will be found on the membrane of red blood cells. For this particular case, at this same locus, instead of having this sequence shown in red, we have a slightly different sequence of nucleotide shown in blue that codes for a different protein.