The pleiotropic is a type of genetic behaviour which influence and affect more than one trait. Sickle cell anemia disease is a type of pleiotropism. In sickle cell anaemia patients, haemoglobin A is entirely replaced with haemoglobin S. Such patients have the genotype HBs HBs. Heterozygotes who carry the sickle cell gene HBa HBs are said to have a condition called sickle cell trait thus the expression of two different genotypes by one single gene indicates pleiotropism.
Haemoglobin S crystallizes when oxygen concentration is low in capillaries making the red blood cells to assume a crescent or sickle shape. Such cells transport oxygen very poorly leading to anaemia.
