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 ?
- Phenylketonuria
- Haemophilia
- Sickle-cell anaemia
- Thalassemia
Answer
(3) Sickle-cell anaemia
Solution
Sickle-cell anaemia is an autosomal recessive Mendelian disorder.
As per NCERT, it is caused by the substitution of glutamic acid (Glu) by valine (Val) at the sixth position of the β-globin chain of haemoglobin.
∵ The single base substitution changes the codon GAG to GUG.
⇒ The mutant haemoglobin polymerises under low oxygen tension ⇒ RBCs change from biconcave disc to elongated sickle-like shape.
Answer: (3)