Hemoglobin gene, introns

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.

Figure 29,35 A splicing mutation that causes thalassemia. An A to-G miutation within the first intron of the gene for tlie human hemoglobin (3 chain creates a new 5 splice site (GU). Both 5 splice sites are recognized by the U1 srtRNP so splicing may sometimes create a normal mature mRNA and an abnormal mature mRNA that contains intron sequences. The normal mature mRNA is translated into a fiemoglobin (3 chain. Because it includes intron sequences, the abnormal mature mRNA now has a premature stop codon and is degraded.

Globin Gene Structure - Figure 7.20 shows how the exon - intron structure of the hemoglobin... 

Some types of -thalassemia (little or none of the hemoglobin p chain produced) are caused by homozygous mutations in the splice junction sequences at intron/exon boundaries. In some individuals, an AT replaces a GT in the gene at the 5 end of the first or second intron. Mutations also occur within the splice junction sequences at the 3 -end of introns (GT at the donor site 5 -end and AG at the acceptor site 3 -end). Mutations at either site totally abolish normal splicing and result in p thalassemia. 

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