In developing humans, the γ hemoglobin subunit is expressed approximately 10 weeks following conception until birth. The γ subunit substitutes the β subunit, typically found in adult hemoglobin. The developing fetus produces the γ subunit because of its higher affinity for oxygen compared to the β subunit at the standard partial pressure for oxygen (150 mmHg).

Recently, researchers identified a family with an unusual disorder. Some members of this family exhibit pulmonary developmental problems in utero. To investigate the etiology of the disorder, the researchers performed several experiments in which DNA samples, from the family, and hemoglobin samples, from the family and control individuals, were collected and studied.

Figure 1. Partial pressure of oxygen versus oxyhemoglobin saturation of normal adult, normal fetal, and disorder fetal hemoglobin.

From the genetic information of the family, a pedigree was constructed.

Figure 2. Pedigree of family with fetal hemoglobin disorder.

A sample of blood was then obtained from a normal fetus and disordered fetus. The hemoglobin proteins were extracted and the γ subunit from each of the type of hemoglobin samples was sequenced.

γ Subunit -Arg-Cys-Val-Phe-Tyr-Ile-Ser-Glu-Phe-Cys-His-
Figure 3. Amino acid sequences of the γ (normal fetus) and γ¹ (disorder fetus) subunits of fetal hemoglobin. This was the only mutated region of the amino acid sequence.γ¹ Subunit -Arg-Cys-Val-Lys-Asp-Ile-Ser-Glu-Phe-Cys-Glu-
.

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