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Sickle cell anemia is
A
Characterized by elongated sickle like RBCs with a nucleus
B
An autosomal linked dominant trait
C
Caused by substitution of valine by glutamic acid in the beta globin chain of haemoglobin
D
Caused by a change in a single base pair of DNA
Detailed Solution
Sickle-cell anaemia is caused by a point mutation: a single base substitution at the sixth codon of the β-globin gene, from GAG to GUG. So it is caused by a change in a single base pair of DNA.
As a result glutamic acid (Glu) is replaced by valine (Val) at the sixth position of the β-globin chain; the given statement has this the wrong way round.
It is an autosome-linked recessive trait; only homozygous individuals ($Hb^SHb^S$) show the disease.
The mutant haemoglobin polymerises under low oxygen tension and changes the RBC from a biconcave disc to an elongated sickle shape; human RBCs have no nucleus.
Hence the correct statement is that it is caused by a change in a single base pair of DNA.
As a result glutamic acid (Glu) is replaced by valine (Val) at the sixth position of the β-globin chain; the given statement has this the wrong way round.
It is an autosome-linked recessive trait; only homozygous individuals ($Hb^SHb^S$) show the disease.
The mutant haemoglobin polymerises under low oxygen tension and changes the RBC from a biconcave disc to an elongated sickle shape; human RBCs have no nucleus.
Hence the correct statement is that it is caused by a change in a single base pair of DNA.