Now, the type of hemoglobin molecule found inside adults is different than the type of hemoglobin that is found inside the fetus. Before we actually see why this is the case, let's discuss what the difference is between the adult and the fetal hemoglobin. So, in adults, we know that the hemoglobin consists of four subunits. Two of these subunits are alpha subunits, and the other two subunits are beta subunits. So we have alpha one and alpha two that combines with beta one and beta two to form a protein tetrimer that we call the dull hemoglobin. So this is what it looks like.