This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Physiology
Fetal hemoglobin contains 
Select and explain. 
A. a 2, ss 2, B. a 2, d 2, C. a 2, g 2, D. None
C: a 2, g 2
Answer: C: a 2, g 2 
Explanation: The blood of the human fetus normally contains fetal hemoglobin (hemoglobin F). Its structure is similar to that of hemoglobin A except that the b chains are replaced by g chains; that is, hemoglobin F is a2g2. The g chains have 37 amino acid residues that differ from those in the b chain. Fetal hemoglobin is normally replaced by adult hemoglobin soon after bihRef: Ganong&;s Review of medical physiology 25th edition. Page: 557