<P> A variant hemoglobin, called fetal hemoglobin (HbF, α γ), is found in the developing fetus, and binds oxygen with greater affinity than adult hemoglobin . This means that the oxygen binding curve for fetal hemoglobin is left - shifted (i.e., a higher percentage of hemoglobin has oxygen bound to it at lower oxygen tension), in comparison to that of adult hemoglobin . As a result, fetal blood in the placenta is able to take oxygen from maternal blood . </P> <P> Hemoglobin also carries nitric oxide (NO) in the globin part of the molecule . This improves oxygen delivery in the periphery and contributes to the control of respiration . NO binds reversibly to a specific cysteine residue in globin; the binding depends on the state (R or T) of the hemoglobin . The resulting S - nitrosylated hemoglobin influences various NO - related activities such as the control of vascular resistance, blood pressure and respiration . NO is not released in the cytoplasm of erythrocytes but transported by an anion exchanger called AE1 out of them . </P> <P> Hemoglobin variants are a part of the normal embryonic and fetal development . They may also be pathologic mutant forms of hemoglobin in a population, caused by variations in genetics . Some well - known hemoglobin variants, such as sickle - cell anemia, are responsible for diseases and are considered hemoglobinopathies . Other variants cause no detectable pathology, and are thus considered non-pathological variants . </P> <P> In the embryo: </P>

What is the correct name for red blood cells