Hemoglobin genes

Hormone response elements (for steroids, T3, retinoic acid, peptides, etc) act as—or in conjunction with— enhancers or silencers (Chapter 43). Other processes that enhance or silence gene expression—such as the response to heat shock, heavy metals (Cd and Zn +), and some toxic chemicals (eg, dioxin)—are mediated through specific regulatory elements. Tissue-specific expression of genes (eg, the albumin gene in liver, the hemoglobin gene in reticulocytes) is also mediated by specific DNA sequences. 

Sickle cells were first identified by physician James Herrick in a 20-year-old medical student from Grenada in 1910.1 O Sickle cell syndrome refers to a collection of autosomal recessive genetic disorders that are characterized by the presence of at least one sickle hemoglobin gene (HbS).2,3... 

SCA is the homozygous (HbSS) state of SCD in which individuals inherit the mutant hemoglobin gene (HbS) from both parents. The progeny of two carriers will have a 25% probability of having SCD and a 50% risk of being a carrier themselves (Fig. 65-1). P-Thalassemia can be found in conjunction with HbS. Patients with HbSS and HbSjf- thalassemia do not... 

Sickle-cell syndrome A group of autosomal recessive genetic disorders characterized by the presence of at least one sickle-hemoglobin gene. 

What selective advantage does possession of multiple hemoglobin genes provide In fish that possess two types of hemoglobin, one responsive and the other unresponsive to heterotropic ligands, such polymorphism offers a clear advantage. One of the hemoglobins assures the... 

Khosravi, M., Webster, D. Stark, B. (1990). Presence of the bacterial hemoglobin gene improves alpha-amylase production of a recombinant Escherichia coli strain. Plasmid, 24, 190-4. 

DNA Sequence Differences Were Used to Detect Defective Hemoglobin Genes... 

Kollia, P., E. Fibach, S.M. Najjar, A. Schechter, and C.T. Noguchi (1996). Modifications of RNA processing modulate the expression of hemoglobin genes. Proc. Natl. Acad. Sci. USA 93 5693-5698. 

Be able to describe the distribution of the various hemoglobins genes. 

Figure 14.4 Arrangement of hemoglobin genes along human chromosomes 11 and 16. Boxes are transcribed genes, and the horizontal thin lines are intervening, untranscribed spaces. Exons are shaded black, and introns that are removed from mRNA are white. 4> are pseudogenes with sequences resembling genes but are not transcribed. The scheme is roughly to scale.

All the following statements about hemoglobin genes are true, except... 

The expression of mammalian hemoglobin genes is regulated only posttranscrip-tionally. Why ... 

Nil. Neel, J. V., The hemoglobin genes a remarkable example of the clustering of related genetic functions on a single mammalian chromosome. Blood 18, 769-777 (1961). 

P3. Pearson, H. A., and Moore, M. M., Human hemoglobin gene linkage report of a family with hemoglobin Bj, hemoglobin S and 0 thalassemia including a possible crossover between thalassemia and delta loci. Amer. J. Hum. Genet. 17, 125-132 (1965). 

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