Question

only homozygous individuals for hbsshow the diseased phenotype why in sickle cell anaemia

Answer 1

The sickle cell trait is widespread throughout Africa with low frequencies (<1%–2%) in the north and south of the continent and high but variable frequencies throughout much of equatorial Africa. Characterization of the DNA structure flanking the β-globin locus of HbS suggests that the mutation has arisen on at least three independent occasions in the African continent, referred to as β-globin haplotypes and named after the areas where they were first described: Benin, Senegal, and Central African Republic or Bantu (Pagnier et al. 1984; Nagel et al 1985; Chebloune et al. 1988). The HbC trait is believed to be a relatively recent mutation limited to West Africa where it occurs at high frequencies (>20%) in central Ghana and Burkina Faso, in only 2% in Nigeria, and does not occur, except in peoples of West African origin, in East and Central Africa. Only limited data are available on the type and distribution of α- and β-thalassemia genes in the African continent.