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
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
