Sickle-cell anaemia is:
- Caused by substitution of valine by glutamic acid in the beta globin chain of haemoglobin
- An autosomal linked dominant trait
- Caused by a change in a single base pair of DNA
- Characterised by elongated sickle like RBCs with a nucleus
Answer
(3) Caused by a change in a single base pair of DNA
Solution
As per NCERT, sickle-cell anaemia is an autosomal recessive trait caused by the substitution of glutamic acid (Glu) by valine (Val) at the sixth position of the beta globin chain.
⇒ This results from a single base substitution (point mutation) in the beta globin gene: GAG → GUG.
(1) has the substitution reversed, (2) the trait is recessive, (4) human RBCs are enucleate.
Answer: (3)