Question

A relevant portion of β-chain of haemoglobin of a normal human is given below:

The codon for the sixth amino acid is GAG. The sixth codon GAG mutates to GAA as a result of mutation ‘A’ and into GUG as a result of mutation ‘B’. Haemoglobin structure did not change as a result of mutation ‘A’ whereas haemoglobin structure changed because of mutation ‘B’ leading to sickle shaped RBCs. Explain giving reasons how could mutation ‘B’ change the haemoglobin structure and not mutation ‘A’.

Answer 1

Due to mutation ‘A’, GAG mutates to GAA. But both GAG and GAA code for glutamic acid and hence there is no change in RBCs. Whereas GUG formed due to mutation ‘B’ codes for valine and so the RBCs become sickle-shaped.