8 4 Thalassaemia is a recessive genetic disorder that affects the production of haemoglobin. It is caused by a gene mutation. Scientists are developing methods to repair gene mutations such as the one that causes thalassaemia. (a) A gene mutation can be a change in a single base in the (1) A DNA that codes for a different amino acid B DNA that codes for a different monosaccharide C RNA that codes for a different amino acid D RNA that codes for a different monosaccharide (b) One of the most common mutations causing thalassaemia is the substitution of one adenine base with guanine. The diagram shows the location of the mutation in part of the DNA strand coding for four amino acids. substitute base C T G G G C A T A G A A Explain why this mutation affects the function of the haemoglobin molecule. (3) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 9 Turn over (c) The RNA produced during transcription is known as pre‑mRNA. Pre‑mRNA can be modified before being translated on the ribosome. (i) Describe how the pre‑mRNA may be modified before being translated on the ribosome. 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(ii) Explain why modification of pre‑mRNA enables one gene to give rise to more than one protein. (2) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (Total for Question 4 = 8 marks)