Which among the following is the major hemoglobin found in fetus?
**Core Concept**
Fetal hemoglobin is a crucial adaptation in the fetus to facilitate oxygen delivery from the mother's bloodstream. It has distinct structural and functional properties compared to adult hemoglobin.
**Why the Correct Answer is Right**
Fetal hemoglobin is composed of two alpha-globin chains and two gamma-globin chains (α2γ2), which allows it to bind oxygen more readily than adult hemoglobin. This property enables the fetus to extract oxygen from the mother's bloodstream, even at the relatively low oxygen tensions found in the placenta. The gamma-globin chains in fetal hemoglobin have a higher affinity for oxygen than the beta-globin chains in adult hemoglobin, allowing for more efficient oxygen delivery.
**Why Each Wrong Option is Incorrect**
* **Option A:** Adult hemoglobin (HbA) is the major hemoglobin found in adults and is composed of two alpha-globin chains and two beta-globin chains (α2β2). While it is also present in the fetus, it is not the major form.
* **Option B:** Hemoglobin F2α is a minor component of fetal hemoglobin, making up only a small percentage of the total. It is not the major form.
* **Option D:** Hemoglobin Portland-1 is an abnormal hemoglobin variant that is not the major form of hemoglobin found in the fetus.
**Clinical Pearl / High-Yield Fact**
The difference in oxygen affinity between fetal and adult hemoglobin is due to the substitution of valine for glutamic acid at position 6 of the beta-globin chain in adult hemoglobin. This substitution reduces the oxygen affinity of adult hemoglobin, allowing for more efficient release of oxygen to tissues.
**Correct Answer: C. Hemoglobin F (HbF)**