Frameshift Mutation
 
A frameshift mutation is a type of mutation that results from the addition or deletion of (3n ± 1( nucleotides (where n is an integer). The addition or deletion of nucleotides that are not multiples of three disrupts the triplet reading frame of the gene. Technically defined, a frameshift mutation is within the coding portion of the gene, but the term is commonly used for any insertion or deletion of a few bases. Frameshift mutations were first described by Crick et al. (1) who used them to decipher the triplet nature of the genetic code. Although point mutations only alter one ) or no) amino acids, frameshifts alter nearly all of the amino acids downstream of the mutation until a nonsense codon is encountered during translation and the polypeptide chain is terminated. Frameshift mutations are induced by a wide variety of intercalating agents, such as ethidium bromide.  
References
1. F. H. C. Crick, L. Barnett, S. Brenner, and R. J. Watts-Tobin (1961) Nature (London) 192, 1227–1232 .