SICKLE CELL ANAEMIA

-An example of hereditary diseases due to gene mutation
-It is an example of base substitution mutation affecting a base in one of the genes involved in the production of haemoglobin
-The disease is mainly confined to Africa or people of the African descent, a proportion of the person’s red blood cells becomes sickle shaped and die.
-This is due to the substitution of valine for glutamic acid in the abnormal polypeptide chains of haemoglobin S.
-The physiological effect is to lower the amount of oxygen which can be carried by the cells.
-Leading to acute anaemia
-In populations where sickle cell anaemia appears, three genotypes are possible. (H=gene for normal haemoglobin; S=gene for sickle haemoglobin).
*HH: the inheritance of a gene for normal haemoglobin from both parents
*HS: the inheritance of one gene for normal haemoglobin and one sickling
*SS: the inheritance of gene for sickling from both parents.
-Sickle cell anaemia develops in people belonging to the child third group (SS)
-People in the second group (HS) are carriers
-If two carriers marry, each of their children have 25% chance at becoming a victim of sickle anaemia and 50% chance of being a carrier.
-Victims are not susceptible to malarial attack.