Gene mutationsEdexcel International A Level Biology: Mind map

Exam questions on Gene mutations

1. In sickle cell anaemia, a change in the gene for the beta chain of haemoglobin alters one codon in the mRNA from GAG, which codes for glutamic acid, to GUG, which codes for valine. All the other codons are unchanged.
   Explain how this change in one codon can alter the properties of the haemoglobin protein.2 marks
2. The mRNA of a gene has the codon sequence AUG GCA UUC GAA UAA. A mutation deletes the first base of the second codon, the G of GCA, and the rest of the mRNA is unchanged.
   Explain why deleting three consecutive bases from the middle of a gene may be less harmful than deleting a single base.2 marks
3. In an mRNA, the codon GAA codes for glutamic acid. The codon GAG also codes for glutamic acid, the codon GAU codes for aspartic acid and the codon UAA is a stop codon.
   Describe and explain the effect on the polypeptide of a substitution that changes the codon GAA to (i) GAG, (ii) GAU and (iii) UAA.3 marks