A point mutation is a single base substitution. It is the smallest type of mutation possible.
In a point mutation, either:
- a single base nucleotide is changed for another nucleotide of the genetic material (normally DNA) or
- a single base pair is inserted or deleted.
A nonsense mutation is a point mutation in a DNA sequence that leads to an early stop codon. This appears as a nonsense codon in the transcribed mRNA. Most of the time, the protein that is translated from this mRNA does not work.