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MCAT Biology Question — Fetal Hemoglobin

An individual is born with a mutation causing her to partially retain a form of fetal hemoglobin into adulthood. Compared to a normal individual, this person would exhibit:


A. no differences from a normal adult.
B. significantly reduced oxygen binding in the lungs.
C. no symptoms, since retention of fetal hemoglobin would be fatal.
D. increased oxygen binding to hemoglobin in the tissues.

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Fetal hemoglobin has a higher affinity for oxygen than does adult hemoglobin. Thus, it binds and holds oxygen more tightly. An individual with fetal hemoglobin would show increased oxygen binding to hemoglobin as a result. (A) is false because fetal and adult hemoglobin are different. (B) is false because fetal hemoglobin binds more to oxygen, not less. And (C) is false – in fact, reactivating fetal hemoglobin can be used as a treatment for sickle-cell. Therefore, the answer is (D).

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