A frameshift is a form of mutation that can occur in living organisms, this occurs by the insertion or deletion of a number of bases that aren't divisible by the number three. This type of mutation can often cause different amino acids to be coded for from the original code, however, due to the degenerate nature of the genetic code an insertion mutation may not always result in a different amino acid being coded for. For example, the codons TTT and TTC (where T = thymine and C = cytosine) both code for the amino acid Phenylalanine. When the resulting amino acids are different, the mutation may result in a different protein being produced which does not perform the same function as before. This is known as a transmuted protein. There is a one in twenty chance that the new codon formed may be a stop codon (also known as a nonsense mutation) which will stop the polypeptide chain from fully being produced. Frameshift mutations can occur through slippages at repeat sequences during replication. It is a very unstable mutation and many different codons can be produced from the wild-type genetic code.
A frameshift mutation is one of many mutations including; base pair changes, deletion, insertion, inversion and duplications.