In african areas that are prone to malaria having normal blood leaves you prone to contracting malaria and death. having sickle cell anemia makes your blood unable to effectively transport oxygen and typically leads to early death. however, being heterozygous for normal blood and sickle cell anemia leads to the blood being able to effectively transport oxygen and resistance to malaria, allowing for a longer life expectancy.

is this directional, stabilizing, or disruptive selection