Mutations - DNA mutations - Point mutations
They are changes to the nucleotide bases. DNA molecules are fairly stable, however, mutations can occur during DNA replication by mitosis or meiosis. Changes to DNA can affect a single locus, which then produces a different allele of a gene.
Somatic mutation = associated with mitosis and are not normally passed onto the offspring. They tend to be unique changes.
Gametic mutation = always passed onto the offspring because mutations are associated with gamete formation and meiosis.
Base mutations: changes to the base sequence --> changes the amino acid sequence in the protein
Point mutations: Only one base is changed (one base pair is replaced with another) so the amino acid sequence after the changed base stays the same. This is known as substitution.
Mis-sense mutation = The base change results in a different amino acid being coded for so the final polypeptide will be different. Example: Sickle cell anaemia - Thymine is substituted by Adenine --> amino acid valine, instead of glutamic acid --> abnormal haemoglobin that is sticky.
Nonsense mutation = protein production is stopped prematuraly because the base change has resulted in the formation of one of the three "stop" codons, which with end the polypeptide chain
Silent mutation = substitution results in a different triplet but it still codes for the same amino acid.