At least six different haemoglobins appear during the
developmental stages of the man. Of these 3 are present during adulthood.
These three haemoglobins are HbF (fetal haemoglobin), present at less
than 1% in the adult, HbA2, present at around the 3% in the
adult and the main adult haemoglobin HbA (97%). These haemoglobins differ
in the non alpha-like globin chains i.e. HbF has two gamma chains, HbA2
has two delta chains and HbA has two beta chains. Each haemoglobin has
also a different oxygen dissociation curve.