Mutations are changes in the DNA that can result in no protein or an altered protein being synthesised.
Single gene mutations involve the alteration of a DNA nucleotide sequence as a result of the substitution, insertion or deletion of nucleotides.
There are three types of single gene mutations that result from nucleotide substitutions: missense, nonsense and splice-site mutations.
A substitution mutation
Missense mutations result in one amino acid being changed for another.
This may result in a non-functional protein or have little effect on the protein.
Nonsense mutations result in a premature stop codon being produced which results in a shorter protein.
Splice-site mutations result in some introns being retained and/or some exons not being included in the mature transcript.
The other type of single gene mutations that result from nucleotide insertion and nucleotide deletion, are frame-shift mutations.
Nucleotide insertions or deletions result in frame-shift mutations.
Frame-shift mutations cause all of the codons and all of the amino acids after the mutation to be changed.
This has a major effect on the structure of the protein produced.
A deletion mutation
An insertion mutation
The other types of mutations are chromosome structure mutations: duplication, deletion, inversion and translocation.
Duplication is where a section of a chromosome is added from its homologous partner.
Deletion is where a section of a chromosome is removed.
Inversion is where a section of chromosome is reversed.
Translocation is where a section of a chromosome is added to a chromosome, not its homologous partner.
The substantial changes in chromosome mutations often make them lethal.
Mutations and gene duplication are important in evolution.
Mutations bring about new variation by the production of new alleles. Without mutations there would be no new variation.
Mutations that result in gene duplication allow potential beneficial mutations to occur in a duplicated gene whilst the original gene can still be expressed to produce its protein.