Sickle cell anaemia is controlled by a single gene mutation (via a base substitution to the haemoglobin beta chain gene)
- The sixth codon is mutated (GAG → GUG) which changes the amino acid sequence (Glu → Val)
Individuals who only possess the sickle cell allele will have abnormally shaped red blood cells that are destroyed by the spleen
- This leads to a reduction in red blood cells and a variety of health complications associated with reduced blood cell circulation
Those who only possess the normal blood cell allele do not suffer from sickle cell anaemia but are more susceptible to malaria
- Malaria is caused by an endoparasite (Plasmodium falciparum) which reproduces inside red blood cells (but not sickle cells)
Incidence of Malaria
In areas where malaria is common, there is a higher incidence of people who carry both alleles (i.e. are heterozygous)
These individuals produce enough normal blood cells to avoid the more severe effects associated with sickle cell anaemia, but also produce enough sickle cells to confer an increased resistance to the malarial parasite
- This condition whereby the presence of both alleles is beneficial is known as heterozygous advantage
Correlation between Prevalence of Sickle Cell Allele and Malaria
