Which of the following is not contained in the buffy coat?

A. Plasma: The pale, straw-colored fluid at the top after centrifugation; it contains water, dissolved proteins (albumin, clotting factors), nutrients, hormones and electrolytes and is about ~55% of whole blood.

B.Buffy coat: The thin, whitish layer that sits between the top plasma and the bottom red cell layer after centrifugation; it contains leukocytes (WBCs) and platelets and makes up <1% of whole blood.

C. Erythrocytes: The dense red layer that settles at the bottom (the hematocrit); composed of red blood cells containing hemoglobin, typically about ~45% of whole blood and responsible for O₂/CO₂ transport.

A. It is a cause of anemia: Sickle cells are fragile and hemolyze prematurely, producing a chronic hemolytic anemia.
B. It is cause of malaria: Malaria is caused by Plasmodium parasites; sickle-cell disease does not cause malaria (in fact, sickle-cell trait provides some protection against severe malaria).
C. It is due to a hereditary hemoglobin defect: Sickle-cell disease is inherited and results from a mutation in the β-globin (HBB) gene producing hemoglobin S.
D. It is advantageous in that it can protect carriers against malaria: Heterozygous carriers (sickle-cell trait) have relative resistance to severe forms of Plasmodium falciparum malaria.
E. It is caused by excessive allele that modifies the structure of hemoglobin: The disease is caused by a point mutation (a single nucleotide change) in the β-globin allele that alters hemoglobin structure (Glu→Val at position 6). Saying “excessive allele” is misleading -the cause is a specific mutant allele, not an “excessive” one.