Question

Sickle Cell anaemia is a case of
A) Transition
B) Transversion
C) Frame shift
D) Silent mutation

Answer 1

There are several blood diseases caused by nutritional disorders, as well as those caused by inherited mutations. Sickle cell anaemia or sickle cell disease is a result of a mutation in a protein chain.

Complete Answer:
- In sickle cell anaemia, instead of their usual doughnut shape, red blood cells assume a crescent or sickle shape. Because of this they tend to clump together rather than flowing freely.
- The oxygen carrying capacity of the haemoglobin is also reduced in these cells. A point mutation in the beta globin gene produces haemoglobin S which makes the erythrocytes bend or sickle. This is due a point mutation which is a substitution of a single Adenine nucleotide for a thymine nucleotide converting a codon for glutamic acid – GAG – to one for valine – GTG. This is a switch of a purine for a pyrimidine base, and is therefore a transversion mutation. Option B is the correct answer.
- A transition mutation involves a pyrimidine being replaced by another pyrimidine or a purine by a purine. In this case, A is replaced by T. That is purine to pyrimidine change. Option A is incorrect.
- A frame-shift mutation is a change in the reading frame of the gene. This would be accomplished by the addition or deletion of one or two nucleotides. Sickle cell anaemia is a kind of substitution. Option C is incorrect.
- In a silent mutation, the switch is in a non-reading frame, or doesn’t affect the final protein product. Here the mutation results in a disorder. Therefore option D is incorrect.

Hence the correct answer is option B.

Note: Sickle cell anaemia is a good example of how a point mutation which is a change at the level of one nucleotide can have disastrous effects. Mild exertion can result in breathlessness, clots, and strokes.