Subsequent to Allison’s discovery, investigators have keen interest in verifying the molecular basis of the variation between HbS (haemoglobin S – characteristic of sickle cell anemia) and HbA (haemoglobin A – characteristic of normal haemoglobin).
a) Protein sequencing revealed that HbS varies from HbA because of a single amino acid substitution i.e. valine in the place of a glutamic acid residue. The single amino acid substitution changes the charge of hemoglobins and produces to combine into long rod like structures within the red blood cells. When the genetic code was translated and process for sequencing DNA (deoxyribonucleic acid) were developed. HbS was influenced to be caused by a single point mutation GAG ? GTC; in consequence ß6 glutamic acid in HbA becomes ß6 valine in HbS.
b) The association between HbS frequency and the occurrence of malaria held across not only East Africa, but the African continent, Southern Europe, and the Indian subcontinent. Allison inferred that the HbS alleles in various regions arose independently, quite than by spreading through migration. In reality, with the initiation of tools for DNA genotyping, it is evident that the HbS mutation has arisen separately in five various haplotypes and then improved to high frequency in specific regions.