Question

Hereditary persistence of fetal hemoglobin Hb gamma(HPFH) is a naturally –occurring genetic variant that moderates the clinical symptoms of B-thalassemia in children and adults. No such comparable sparing of symptoms in a-thalassemia patients has been observed due to persistent expression of the embryonic Hb zeta. Explain the developmental differences in gene expression and function of Hb gamma and Hb zeta that might explain these seemingly inconsistent observations.

Answer 1

ANSWER:-

• All animals that use hemoglobin for oxygen transport have different hemoglobin species during the early and latter stages of development.
• In humans two gene cluster direct the synthesis of hemoglobin: the alpha locus which contains the embryonic gene and two adult alpha genes. and the beta locus which consists of epsilon,G-gamma,A-gamma delta and beta genes.
• Two globin switches occur during development: the embryonic to fetal globin switch, which coincides with the transition from embryonic to definitive hematopoiesis and the fetal to adult switch.
• The switches from epsilon to gamma and from gamma to beta globin gene expression are controlled exclusively at the transcription level.
• The embryonic to alpha switch is controlled predominantly at the transcription level.
• The homozygous delta-beta thalassemia and the homozygous hereditary persistent of fetal hemoglobin were due to deletions that remove the dealta and beta gene but leave the G-gamma and A-gamma genes intact.
• This is due to the switching mechanism. so the delection in HPFH produces a phenotype characterized by abundant and pancellular synthesis of fetal hemoglobin in adult red cells and no disease in homozygotes, while the delection in dealta-beta thalassemia produces the phenotype of heterocellular and less abundant synthesis of fetal hemoglobin in the heterozygotes.

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