Mutations on genetic code atfects the phenotype. Describe with example.

Explanation

The simplest type of mutation at the molecular level is a change in nucleotide that substitutes one base for another. Such changes are known as base substitutions which may occur spontaneously or due to the action of mutagens. A well studied example is sickle cell anaemia in humans which results from a point mutation of an allele of B-haemoglobin gene `(betaHB).`
A hacmoglobin molecule consists of four polypeptide chains of two types, two a chains and two `beta`-chains.
Each chain has a heme group on its surface. The heme groups are involved in the binding of oxygen. The human blood disease, sickle cell anaemia 1s due to abnormal haemoglobin. This abnormality in haemoglobin is due to a single base substitution at the SIxth codon of the beta globin gene from GAG to GTG in `beta` -chain of haemoglobin. It results n a change of amino acid glutamic acid to valine at the 6th position of the `beta` -chain. This is the classical example of point mutation that results in the change of amino acids residue gutamie acid to valine. The mutant haemoglobin undergoes polymerisation under oxygen tensior causing the change in the shape of the RBC from biconcave to a sickle shaped structure.