Mutations and their effectsAQA A-Level Biology: Mind map

Exam questions on Mutations and their effects

1. A short section of the coding strand of a gene reads ATG GAA CTT AAG GGC and codes for the amino acids methionine, glutamic acid, leucine, lysine and glycine. A mutation changes the third base of the second triplet from A to G, giving GAG, which also codes for glutamic acid. A different mutation changes the same triplet from GAA to TAA.
   Explain the effect on the polypeptide of the mutation that changes GAA to TAA.2 marks
2. The coding strand of part of a gene reads CAT GAT TCC AAG and codes for four amino acids. A mutation deletes the first G of the second triplet.
   Explain why a deletion of one base usually has a greater effect on a polypeptide than a substitution of one base.2 marks
3. A researcher grew a culture of bacteria and counted the number of cells that had mutated to become resistant to an antibiotic. In an untreated culture there were 3 resistant cells per million cells. In a culture exposed to ultraviolet light there were 450 resistant cells per million cells. The resistance was caused by a single-base change in a gene coding for a bacterial protein to which the antibiotic normally binds.
   Explain the results of the researcher's experiment.3 marks