Normal HbA→2-alpha and 2-beta. Normally after A the next letter is B, right?
HbA2 or A-Double→2-alpha+2-Delta→also normal, small amounts
HbF (Fetal)→2-alpha+2-Gamma→Fetal Hb has Gamma chains, think of Gametes
HbH has 4-beta chains→3 alpha genes deletion
HbB=Bart→Bart→Baby and Fetus have Fetal Hb (2-alpha and 2-Gamma chains) →HbB has 4-Gamma chains→4 alpha genes deletion→Fetus dies (hydrops fetalis)
Both HbH and HbB have 4 chains, like any other Hb. HbH has 3 alpha genes deletion→the letter H has 3 lines in it (two vertical and one horizontal). HbB is 4×4 (4-alpha chains deletion and 4-beta chains)→think that Bart Simpson drives only 4×4 cars. Don’t confuse chains with deletions. Think of them separately.