Abnormality is in a change from glutamine to valine. In the deoxy form, haemoglobin S starts to polymerise and precipitate put in solution. This distorts the RBC making it rigid and therefore more rigid. This increases the amount of deoxy HbS producing sickled cells.
First signs appear at approx.
Hb has the same charge and mobility as normal Hb. The Tyr stabilises the iron in an oxidised state, imparting a brownish colour to the blood with no other haematologic abnormality Increased Oxygen Affinity eg.