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Describe the evolutionary development of the hemoglobins from embryo to adult.

Hemoglobin is tetramer of 4 globin chain + heme( Fe containing porphyrin ring).

Normally 6 different types of Hb may be found along the evolutionary period from embryo to adult:

Embryonic:

Gower 1     ζ2 ε2
Gower 2     α2 ε2
Portland       ζ2 γ2

  • 6wk gestation: 1st globin switch to fetal hb
  • Upto 6wk Gower hb predominate, no longer detectable by 3mo gestation

Fetal:

Hemoglobin F      α2 γ2

  • By 6-8wk HbF is predominate hb
  • By 24wk HbF constitute 90% of Hb
  • By 6-12mo postnatal age <2% of Hb

Adult:

Hemoglobin A     α2 β2

  • By 24wk gestation HbA is 5-10% Hb (∵ 2nd  globin switch by transcription factor BCL11A binds to β globin gene and silence γ gene)
  • At term, HbA is 30% of Hb
  • By 6-12mo HbA reaches adult HbA levels

Hemoglobin A2     α2 δ2

  • At birth, HbA2 is <1%
  • By 12mo, HbA2 is 2 -3.4%
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