Haemoglobin

There are different types of haemoglobin. The usual type of haemoglobin is called "haemoglobin A" or "Hb A". When you have Hb A your red blood cells are round, flexible "doughnut shaped" cells that pass through blood vessels easily. If you inherit normal haemoglobin from each parent then you do not have Sickle Cell or Thalassaemia. This means that you have "Hb AA".

Some other more common unusual haemoglobins are "Haemoglobin S", Haemoglobin C", "Haemoglobin D", and "Haemoglobin E", although there are many more. If you inherit any one of these unusual haemoglobins from one parent and a normal haemoglobin gene from the other parent (Hb A) then you will carry a "Trait", Sickle Cell Trait is "Hb AS".

If you inherit two of a certain kind of the unusual haemoglobins, one from each parent ( i.e. HB S ), then you will have a "disorder", i.e. Sickle Cell Disorder is "Hb SS". Some disorders are more severe than others.