Gene Mutation

Question 1

Sickle-cell anaemia

Answer 1

1. In sickle-cell anaemia, single base pair substitution in the gene coding for the b-chain causes adenine to replace thymine
2. DNA triplet changes from CTC to CAC
3. In the mRNA formed, GUG is coded for instead of GAG, resulting in hydrophobic valine replacing hydrophilic glutamic acid in the 6th amino acid position of the b-chain
4. This results in a change in 3D conformation of haemoglobin to produce HbS instead of HbA
5. This decreases solubility of deoxygenated HbS, and at low O2 concentrations, different HbS molecules stick together
6. HbS molecules polymerise and form rigid fibres
7. RBC changes from circular biconcave shape to sickle cell shape, and may block capillaries, impeding blood flow.
8. This deprives organs of oxygen, resulting in organ damage.

Question 2

Types of gene mutation

Answer 2

1. Base pair substitution
2. Base pair deletion
3. Base pair addition

Question 3

Consequences of gene mutation