Summary OCR A-Level Biology 6.1.1 Gene Mutations

Gene Mutations
Mutation
 Occur spontaneously during DNA replication – rare due to checkpoints
 Mutagens increase the risk of mutation and are described as mutagenic
 Chemical Agents e.g. tobacco smoke, mustard gas, synthetic dyes
 Physical Agents (ionizing radiation) e.g. gamma rays, X-rays, UV light
 Biological Agents e.g. viruses, transposons, food contaminants



Indel Mutations
 Result in a frameshift – all subsequent amino acids are affected, altering the rest of the
primary structure (sequence) meaning the protein is unlikely to have any biological use
 Insertion – additional nucleotides inserted into the DNA strand
 Deletion – nucleotides removed (deleted) from the DNA strand



Point Mutations
 A nucleotide is replaced with a different nucleotide
 Silent Mutation – because the DNA code is degenerate, most amino acids are coded for
by multiple different triplets, so sometimes, point mutations result in the same amino
acid being coded for
 Missense Mutation – a point mutation that leads to a change in the amino acid coded
for
 Nonsense Mutation – a point mutation alters a base triplet to make it into a termination
(stop) triplet