During embryonic development, which globin chain functionally replaces the adult β chain in embryonic hemoglobins?
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ADelta (δ)
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BEpsilon (ε)
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CGamma (γ)
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DAlpha (α)
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EZeta (ζ)
Answer
Correct Answer: Epsilon (ε)
Explanation
Introduction:Hemoglobin expression is developmentally regulated. Distinct globin chains are expressed in embryonic, fetal, and adult stages to optimize oxygen delivery across changing physiological conditions.
Given Data / Assumptions:
- Embryonic hemoglobins (e.g., Hb Gower-1, Hb Gower-2) are under consideration, not fetal HbF or adult HbA.
- Adult β chains are minimal or absent during early embryogenesis.
Concept / Approach:
Embryonic hemoglobins pair ζ (zeta, α-like) with ε (epsilon, β-like) chains. Later, fetal hemoglobin uses γ (gamma) instead of β; finally, adult hemoglobin uses β with α.
Step-by-Step Solution:
1) Embryo: ζ and ε chains dominate (β is not yet expressed).2) Fetus: γ replaces ε in β-like role (HbF: α2γ2).3) Adult: β chains replace γ (HbA: α2β2).Verification / Alternative check:
Globin gene clusters show temporal switches: ε (embryo) → γ (fetus) → β (adult).
Why Other Options Are Wrong:
γ is fetal, not embryonic; δ is a minor adult chain; α is present but does not replace β in the β-like role; ζ is α-like, not β-like.
Common Pitfalls:
Confusing fetal (γ) with embryonic (ε) hemoglobins.
Final Answer:
Epsilon (ε)