Biology – The roles of genes in determining the phenotype | e-Consult

The HBB gene provides the genetic code for one of the two alpha-globin chains of haemoglobin. Haemoglobin is a protein found in red blood cells that is responsible for carrying oxygen throughout the body. The HBB gene encodes a specific amino acid sequence within the alpha-globin chain.

Sickle cell anaemia is a genetic disorder caused by a single nucleotide polymorphism (SNP) in the HBB gene. This SNP results in a change in the DNA sequence, leading to a substitution of a single amino acid (glutamic acid to valine) in the beta-globin chain of haemoglobin. This seemingly small change alters the haemoglobin protein's structure. Specifically, it causes haemoglobin molecules to polymerise under low oxygen conditions, forming long, rigid fibres.

This polymerisation distorts the shape of red blood cells from their normal biconcave disc shape to a sickle shape. These sickle-shaped red blood cells are less flexible and can become trapped in small blood vessels, leading to pain, organ damage, and other complications. The phenotypic consequence is anaemia, pain crises, and various organ-specific problems.

Key processes involved: Gene mutation, Protein structure, Protein function, SNP, Phenotype.