Insertions can be particularly hazardous if they occur in an
exon, the
amino acid coding region of a
gene. A
frameshift mutation, an alteration in the normal
reading frame of a gene, results if the number of inserted nucleotides is not divisible by three, i.e., the number of nucleotides per
codon. Frameshift mutations will alter all the amino acids encoded by the gene following the mutation. Usually, insertions and the subsequent frameshift mutation will cause the active
translation of the gene to encounter a premature
stop codon, resulting in an end to translation and the production of a truncated protein. Transcripts carrying the frameshift mutation may also be degraded through
Nonsense-mediated decay during translation, thus not resulting in any protein product. If translated, the truncated proteins frequently are unable to function properly or at all and can result in any number of genetic disorders depending on the gene in which the insertion occurs. In-frame insertions occur when the reading frame is not altered as a result of the insertion; the number of inserted nucleotides is divisible by three. The reading frame remains intact after the insertion and translation will most likely run to completion if the inserted nucleotides do not code for a stop codon. However, because of the inserted nucleotides, the finished protein will contain, depending on the size of the insertion, multiple new amino acids that may affect the function of the protein. ==See also==