Types of Mutation

Insertion

When nucleotide bases are added into a sequence, can be one or multiple.

Deletion

When nucleotide bases are lost from a sequence, can be one or multiple.

Indel

Term for when either an insertion or deletion has occurred.

Point mutation

A point mutation is a change in one base of the sequence to another. For example, given the sequence ATGCGA, CTGCGA would be an example of a point mutation where the first base A has been replaced by C. This only affects the codon the point mutation happens in. 

Fun fact - as some amino acids are encoded for more than one codon, some point mutations are silent in the sense they do not change the base. This occurs more often when the point mutation is in the third position of a codon. 

Frameshift

A frameshift occurs when an insertion or deletion of bases occurs that isn't a multiple of three bases. This leads to amino acids further down stream being completely different.

The image below shows a defined allele sequence and an isolate sequence. A single base insertion (not a multiple of three), leads to a frameshift. If you look at the amino acid sequences shown below, you can see a frameshift can completely change the amino acid sequence.

Out of frame

Out of frame refers to an amino acid/stop codon that is not in the frame of the gene. This occurs when there's a frameshift. In the sequence above, the last three bases coded TCA which is the amino acid S (serine). Due to the insertion in the isolate sequence, the three bases in that position is now GTC encoding V (valine). The original TCA (S) would be referred to as out of frame, as it is not in the same frame as the start codon anymore. 

Internal stop codon

An internal stop codon is a stop codon found within the body of a gene (we have also called this an additional stop codon). It can be caused by frameshifts or point mutations.