Final answer:
The sickle cell (HbS) allele is carried in red blood cells, causing them to take on a sickle shape, leading to health complications. It is a genetic trait that confers resistance to malaria among carriers, affecting over 100 million people worldwide primarily of African descent. The allele is inherited in an autosomal recessive pattern.
Step-by-step explanation:
The sickle cell (HbS) allele is carried within the red blood cells (erythrocytes) and not the plasma. This allele codes for an abnormal type of hemoglobin, termed hemoglobin S, which can cause erythrocytes to take on a characteristic sickle or crescent shape. The sickle cell allele is inherited in an autosomal recessive pattern, meaning that individuals who are homozygous for the allele (ss) will express the full range of symptoms associated with sickle cell anemia, while heterozygotes (Ss) may have some normal hemoglobin and generally exhibit fewer or no symptoms.
Sickle cell anemia has a significant distribution among certain populations globally. It affects more than 100 million people worldwide, including a substantive portion of those with African heritage. The abnormal hemoglobin in sickle cell anemia changes the shape of red blood cells, particularly under low oxygen conditions, leading these cells to become lodged in capillaries, causing pain and potentially serious health complications.
Historically, the origin of the sickle cell mutation has been traced back to regions in Africa, with heterozygous carriers having a selective advantage due to the allele's protective effect against malaria.