The main purpose of erythrocytes is to:

A. Western European is incorrect because sickle cell anemia is rare among individuals of Western European descent. While carriers exist, the prevalence is much lower than in populations of African ancestry.

B. Native American is incorrect because sickle cell anemia is uncommon in Native American populations. Other hemoglobinopathies, like thalassemia, may be more prevalent in specific indigenous groups.

C. African is correct because sickle cell anemia is caused by a recessive mutation in the HBB gene, which affects the beta chain of hemoglobin. This mutation leads to the production of abnormal hemoglobin S, causing red blood cells to adopt a sickle shape under low oxygen conditions. Sickle-shaped cells are rigid, sticky, and prone to hemolysis, leading to anemia, vaso-occlusive crises, and organ damage. The gene is more commonly found in individuals of African descent, as heterozygosity (carriers) provides some protection against malaria, which historically explains the high prevalence in Africa.

D. Asian is incorrect because sickle cell anemia is relatively rare in Asian populations. Other hemoglobin disorders, such as thalassemia, are more common in Southeast Asian and Mediterranean populations.

A. Transport oxygen from the lungs to the tissues is correct because erythrocytes (red blood cells) contain hemoglobin, a protein that binds oxygen in the lungs and carries it to tissues and organs throughout the body. Hemoglobin also plays a role in transporting a small portion of carbon dioxide back to the lungs, but the primary function of erythrocytes is oxygen delivery.

B. Form blood clots to stop bleeding is incorrect because this is the function of platelets (thrombocytes), which aggregate at sites of vascular injury to initiate clot formation and prevent excessive blood loss.

C. Remove carbon dioxide from the body is incorrect because, although erythrocytes assist in transporting some carbon dioxide from tissues to the lungs, this is not their main purpose. Carbon dioxide removal is a secondary function compared with oxygen transport.

D. Produce antibodies for immune responses is incorrect because antibody production is performed by B lymphocytes (a type of white blood cell). Erythrocytes do not have immune functions and are solely involved in gas transport.