What sub-units are found in fetal hemoglobin instead of beta sub-units?

Fetal hemoglobin, known as hemoglobin F (HbF), is composed of two alpha sub-units and two gamma sub-units, which differentiate it from adult hemoglobin (hemoglobin A) that contains two alpha and two beta sub-units. The presence of gamma sub-units in fetal hemoglobin allows for a higher affinity for oxygen compared to adult hemoglobin. This is crucial for fetuses, as it enables them to effectively extract oxygen from maternal blood in the placenta, where oxygen levels are lower than in adult circulation. This adaptation is vital for fetal development and ensures that the growing fetus receives adequate oxygen supply despite its unique environment.