Cloning and sequencing of the γ-globin gene of a sickle cell anemia patient homozygous for the Bantu haplotype has revealed a gene conversion that involves the replacement of an (A)γ sequence by a (G)γ sequence in the promoter area of the (A)γ gene. This event is similar to another gene conversion believed to be responsible for the very high homology between γ-globin genes, suggesting that the promoter area of these genes is prone to this type of genetic rearrangement. Further analysis demonstrated that the chromosome bearing this gene conversion has a very high frequency among Bantu chromosomes and a very low or nil frequency in other haplotypes linked to the β(s) gene. No correlation was found between (G)γ/(A)γ ratio and the presence of the gene conversion among Bantu haplotype patients, thus excluding a portion of the γ gene sequence in the determination of this ratio.
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