There is disagreement about the site of the human hemoglobin structural genes, mapping of which has been attempted by in situ hybridisation and family studies. After in situ hybridisation of human metaphase chromosomes with radioactive globin mRNA Price et al. suggested that the hemoglobin structural genes are located on the long arm of chromosome 2 and on the long arm of a B group chromosome, the latter carrying the genes for β, γ and δ chains. Their approach was criticised because of the low specific activity of the 3H mRNA assay used. Finally it was decided that the B group chromosome that carries hemoglobin loci is chromosome 4. Family studies gave results consistent with loose linkage between the locus of the MN blood group and β thalassaemia. The MN blood group has been mapped tentatively on the long arm of chromosome 2 or on the distal end of the long arm of chromosome 4. But the localisation of MN system on 2q is inconsistent with data from family studies, and the distal segment of 4q has been considered more probable. For similar reasons the β globin locus has been mapped tentatively on chromosome 4. The authors report here a study of globin synthesis which confirms that chromosome 4 is the site of the structural gene for α globin.
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