Sickle cell anemia Autosomal recessive disorder Homozygous state of HbS (SS) where S stands for gene coding HbS. Heterozygous state of HbS (SA) where A stands for absent gene. Normal individual has no gene for HbS (AA) If the mother has sickle cell disease 'SS' and father is normal 'AA', then all the offsprings will be 'SA'. Thus % of sickle cell disease (SS) will be zero and that of sickle cell trait (SA) will be 100%.