And when these four subunits create the tetrimer fetal hemoglobin, notice we no longer have that space inside the hemoglobin that can accommodate the two three BPG. And so, unlike the Dull hemoglobin, the fetal hemoglobin in the presence of two three BPG does not actually bind to two three BPG. And what that means is if we compare the affinity of these two hemoglobin molecules in the presence of the same concentration of two three BPG, we see that because the fetal hemoglobin doesn't actually bind the two, three BPG, that means its affinity for oxygen will be much higher than the affinity for oxygen of adult hemoglobin. And if we plot this curve on the x y axis, where the x axis is the partial pressure of oxygen given in millimeters of mercury, and the y axis is the percent saturation of that hemoglobin, we get the following curve. So the blue curve is the curve that describes the adult hemoglobin, while the red curve describes the fetal hemoglobin. And notice at the same partial pressure, let's say at 40 degrees partial pressure of oxygen, the adult hemoglobin has much less saturation than the fetal hemoglobin does.