|MoBio||Mutations and Consequences||Chapter 7|
Mutation refers to the change in a DNA sequence, which may involve only a few bases or the large-scale chromosome abnormality. This section covers the small-scale mutations (substitution, deletion, insertion) and the exon skipping that results from mutation at the splice site. The chromosome abnormality is discussed in Chapter 8 Section E.
In the substitution mutation, one or more nucleotides are substituted by the same number of different nucleotides. In most cases, only one nucleotide is changed. Based on the change in the nucleotide type, the substitution mutation may be divided into transition and transversion mutations. Based on the consequence of mutation, the substitution mutation may be grouped into silent, missense and nonsense mutations.
The deletion mutation involves elimination of one or more nucleotides from a DNA sequence. It may cause frameshift, producing a non-functional protein.
Note that deletion and insertion mutations often occur in the repetitive sequence. As explained in the next section, they are usually caused by "replication slippage".
In the insertion mutation, one or more nucleotides are inserted into a sequence. If the number of inserted bases is not a multiple of 3, it will cause frameshift, resulting in serious consequences. As shown in the following table, non-frameshift insertions may also cause diseases.
Table 7-E-1. Examples of diseases caused by insertion mutation.