Now, this is normal hemoglobin that is found in our bodies. But when the fetus is developing inside the mother, the gene that expresses the hemoglobin expresses a slightly different hemoglobin. So the fetal hemoglobin molecule also contains the alpha one and the alpha two subunits, but it does not contain beta one and beta two. Instead, it contains a slightly different type of submune we call gamma one and gamma two. Now, what's the major difference between the beta and the gamma subunits? Well, as it turns out, in the gamma subunit, the gamma subunit does not have histidine 143.