Mutations at the base level occur when there is a mistake in copying the genetic information. There are different types of mutation.

Synonymous mutations - the base changes but the amino acid encoded does not.

In amino acid changing mutations, a change in a base results in a different amino acid being encoded.

In a frame-shift mutation a base is inserted with the result that the following bases are all a base further than their original position on the chromosome.

In a stop mutation an amino acid encoding triplet mutates to a stop codon.