Point mutation

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Illustration of three types of point mutations.

A point mutation is a single base substitution. It is the smallest type of mutation possible.

In a point mutation, either:

  1. a single base nucleotide is changed for another nucleotide of the genetic material (normally DNA) or
  2. 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.