Question

Which one of the following disorders is caused by the substitution of Glutamic acid (Glu) by Valine (Val) at the sixth position of the beta globin chain of the haemoglobin molecule?

• A. Thalassemia
• B. Haemophilia
• C. Sickle-cell anaemia
• D. Phenylketonuria

Hint:

To remember the mutation: Glu (Good) becomes Val (Vile) at position 6 because of a change from A to U in the codon.

Answer 1

The Correct Option is C

Sickle-cell anaemia is an autosome-linked recessive trait that can be transmitted from parents to offspring when both partners are carriers for the gene. The molecular basis of the disease is a specific point mutation:
• The Mutation: There is a substitution of Glutamic acid (Glu) by Valine (Val) at the sixth position of the beta ($ \beta $) globin chain of the haemoglobin molecule.
• Genetic Cause: This protein change is due to a single base substitution at the sixth codon of the beta-globin gene from GAG to GUG.
• Physiological Effect: The mutant haemoglobin molecule undergoes polymerisation under low oxygen tension, causing a change in the shape of the Red Blood Cell (RBC) from a biconcave disc to an elongated, sickle-like structure.