One-quarter of all aboriginal inhabitants of Sub-Saharan Africa carry the gene . In areas where malaria is common , there is a survival value in carrying only a single sickle-cell gene ( sickle cell trait ) .
One-third of all indigenous inhabitants of Sub-Saharan Africa carry the gene , because in areas where malaria is common , there is a fitness benefit in carrying only a single sickle-cell gene ( sickle cell trait ) .