When does switchover from fetal to adult hemoglobin synthesis begin –: (A) 14 weeks gestation, (B) 30 weeks gestation, (C) 36 weeks gestation, (D) 7–10 days postnatal
Answer is C. Fetal Hb → (α2 γ2)
Adults Hb → (α2 β2)

During the initial fetal life, the major haemoglobin synthesized in the body is fetal haemoglobin, because, in the fetus, the chain synthesized predominantly is the γ chain.
the β chain is present in only trace amount in early embryos
The rate of synthesis of y and β chains and the amount of HbA and HbF are inversely related during the intrauterine stage.
As the age of the fetus increases, the synthesis of β chains and the amount of adult haemoglobin in the blood increases
At 36 weeks of gestational age the rate of synthesis of (β chain exceeds that of γ chain. This is called switch over.