What Are the Sickle-Cell Trait and Sickle-Cell Disease?
When a person carries one HbS and one HbA gene, the presence of the normal gene is sufficient to override the effects of the HbS gene so The shape of sickled red blood cells compared to normal red blood cells. the symptoms of sickle-cell disease do not develop. These people, however, are said to have the sickle-cell trait or to be carriers of the sickle-cell trait, and they may pass it on to their children. Prospective parents who are likely to carry the HbS gene may wish to be tested for its presence and receive genetic counseling before having children. When people inherit two abnormal HbS genes, one from each parent, they have sickle-cell disease, and they show symptoms of that disease. They have only abnormal HbS genes to pass on to their children. Since sickle-cell disease is a genetic disorder, its frequency varies in different populations worldwide. It is found most frequently in Africa, where in some locations up to 40 percent of the population has at least one HbS gene. The ge
