There are 4 alpha-chains.

In each chromosome 16 there are two alpha-chains. Two on each chromosome.

If an individual has three alpha-chains, alpha-chain production is 75% and the person is a silent carrier.

A person may have alpha-thalassemia trait if they have two alpha-chain, or 50% alpha-chain production. These people may exhibit mild symptoms of alpha-thalassemia

In HbH, there is only one alpha-chain, meaning 25% alpha-chain production. Clinical manifestations arise from this disease

Hb Bart's is the hemoglobin associated with Hydrops fetalis. In this, there are no alpha-chains. It is characterized by blood in the fetus brain. There are no functional alpha-chains. 0% alpha-chain production.

In Hb Bart's there are 4 gamma chains rather than 4 alpha-chains.

The alpha-chain is produced way before birth. Alpha-chain production shoots up way before birth. After 6 weeks of conception, there is full production of alpha-chains.

The gamma-chain will plateau before birth, but significantly decreases after birth.

The beta-chain will be low way before birth, but after birth, starts to shoot up, around 6 weeks.

The delta-chain will shoot up after birth, but will maintain very low levels.

Thalassemias are a group of inherited disorders characterized by reduced synthesis of one or more globin chains.

Alpha-Thalassemia is a mutation in one or all four genes for the alpha-chain.

There are different alpha-thalassemias: alpha-thalassemia-2, alpha-thalassemia-trait, hemoglobin H disease, and hydrops fetalis.