Principles of Inheritance and Variation — BIOLOGY STD 12 Science — Question

3. Sickle cell anaemia

Explanation:

A mutation is a type of mutation in which only one or few nucleotides are changed in a gene sequence. Sickle-cell anaemia is caused by a point mutation in the β - globin chain of haemoglobin. As a result, the hydrophilic amino acid, glutamic acid is replaced with the hydrophobic amino acid, valine at the sixth position.

Typhoid fever is a bacterial disease caused by the bacteria Salmonella typhi or Salmonella paratyphi.

Night blindness is caused by vitamin A deficiency.

Down's syndrome is a chromosomal abnormality called as trisomy 21 in which an extra copy of the chromosome 21 is present.