Final answer:
Sickle cell anemia is a condition that affects mostly African people and is characterized by crescent-shaped red blood cells that have difficulty entering capillaries when oxygen is low.
Step-by-step explanation:
Sickle cell anemia is the condition that affects mostly African people and is characterized by crescent-shaped red blood cells that make it difficult to enter capillaries when oxygen is low. The abnormal shape of the red blood cells in sickle cell anemia reduces their ability to deliver oxygen and causes them to get stuck in narrow blood vessels. This can lead to a variety of serious problems like painful joints, delayed growth, and even blindness and strokes.