Mutation

Modification of the genome

Mutations occur more-or-less randomly throughout the genome and may affect any gene. There may be no perceptible consequences if the mutation site is not translated into protein or involved in regulation (e.g. mutation in an “intron”). Mutations can occur spontaneously or can be induced artificially by certain chemicals called “mutagens” or ionising radiation.
Different kinds of mutations exist:

• An insertion is the integration of an additional fragment into the DNA.
• A deletion is the elimination of a DNA fragment.
• An inversion is the reversal of a DNA fragment by excision and re-integration in the opposite direction.
• A substitution is the replacement of a base (A,T,C, or G) with another.
  

A mutation can be a change in a single base pairs or can involve a longer DNA fragment. The length of the changed DNA does not necessarily correspond with the impact of the mutation: in some cases, the exchange of a single base pair can have devastating consequences while, in other cases, a change in a long DNA segment may have no recognisable effect at all.