Soon after birth, however, this is largely replaced by adult hemoglobin.

Normal adult hemoglobin is composed of two alpha and two beta chains.

Normal adult hemoglobin contains 2 alpha and 2 beta subunits.

This removes adult hemoglobin, but not fetal hemoglobin, from the red blood cells.

Fetal hemoglobin's affinity for oxygen is substantially greater than that of adult hemoglobin.

Shortly after birth, all but 1 percent of fetal hemoglobin is replaced by adult hemoglobin.

As we can see in the following image, fetal hemoglobin has more affinity to oxygen than adult hemoglobin.

In the tetrameric form of normal adult hemoglobin, the binding of oxygen is, thus, a cooperative process.

The γ subunit has fewer positive charges than the adult hemoglobin b subunit.

Hematologically, however, this is innocuous because only 2-3% of normal adult hemoglobin is hemoglobin A2.

This protein plays a role in erythroid development by regulating the switch of fetal hemoglobin to adult hemoglobin.

Its dissociation curve to oxygen is shifted to the left, meaning that it will take up oxygen at a lower concentration than adult hemoglobin will.

In newborns, fetal hemoglobin is nearly completely replaced by adult hemoglobin by approximately 6 months postnatally.

Soon after, adult hemoglobin (hemoglobin A in particular) takes over as the predominant form of hemoglobin in normal children.

When fetal hemoglobin production is switched off after birth, normal children begin producing adult hemoglobin (HbA).

In addition to differences in circulation, the developing fetus also employs a different type of oxygen transport molecule than adults (adults use adult hemoglobin).

Fetuses are highly susceptible to carbon monoxide damage because fetal hemoglobin binds more tightly to this poison than adult hemoglobin does.

This enables fetal hemoglobin to absorb oxygen from adult hemoglobin in the placenta, which has a lower pressure of oxygen than at the lungs.

These levels decline after six months as adult hemoglobin synthesis is activated while fetal hemoglobin synthesis is deactivated.

If the solution turns yellow-brown, the hemoglobin is maternal or adult hemoglobin, which is less stable than fetal hemoglobin.

This lowered affinity allows for adult hemoglobin (the maternal hemoglobin of the mother) to readily transfer its oxygen to the fetal hemoglobin.

This includes patients who have a special form of hemoglobin known as Hb Chesapeake, which has a greater inherent affinity for oxygen than normal adult hemoglobin.

For example, embryonic and fetal hemoglobin have higher oxygen affinity than adult hemoglobin giving them improved functionality in hypoxic environments such as the uterus.

Fetal hemoglobin is resistant to alkali (basic) denaturation, whereas adult hemoglobin is susceptible to such denaturation.

Two alpha chains plus two delta chains constitute HbA-2, which with HbF comprises the remaining 3% of adult hemoglobin.

The composition of normal adult haemoglobin is designated.

Fetal haemoglobin (HbF) is structurally different from normal adult haemoglobin (HbA).

At the placenta there is a higher concentration of 2,3-DPG formed which binds more readily to adult haemoglobin and not to fetal haemoglobin.

In heterozygous people, that is, those who have only one sickle gene and one normal adult haemoglobin gene, the condition is referred to as "HbAS" or "sickle cell trait".