text: 由于控制α-链合成的4个基因均缺失，故无α-链合成，因此不能合成含α-链的HbA、HbA2</sub>和HbF，在胎儿后期γ、β链各自形成大量的γ4</sub>（HbBart）和β4</sub>（HbH），同时胚胎早期ζ链合成代偿性增加并持续至整个胎儿期，并与α链组成HbPortland。
entities.entity: α-链
entities.label: bod
entities.entity: 基因
entities.label: bod
entities.entity: α-链
entities.label: bod
entities.entity: α-链
entities.label: bod
entities.entity: HbA
entities.label: bod
entities.entity: HbA2</sub>
entities.label: bod
entities.entity: HbF
entities.label: bod
entities.entity: γ、β链
entities.label: bod
entities.entity: γ4</sub>
entities.label: bod
entities.entity: HbBart
entities.label: bod
entities.entity: β4</sub>
entities.label: bod
entities.entity: HbH
entities.label: bod
entities.entity: ζ链
entities.label: bod
entities.entity: α链
entities.label: bod
entities.entity: HbPortland
entities.label: bod