<unk> s can occur randomly or be caused by an external stimulus. The detection of<unk> s can occur via several different methods.<unk> s are just one type of<unk>  that can lead to incomplete or incorrect proteins, but they account for a significant percentage of errors in DNA. Genetic or environmental This is a genetic<unk>  at the level of nucleotide bases. Why and how<unk> s occur are continually being sought after. An environmental study, specifically the production of UV-induced<unk> s by DNA polymerases deficient in 3′ → 5′ exonuclease activity was done. The normal sequence 5′ GTC GTT TTA CAA 3′ was changed to GTC GTT T TTA CAA (MIDT) of GTC GTT C TTA CAA (MIDC) to study<unk> s. E. coli pol I Kf and T7 DNA polymerase mutant enzymes devoid of 3′ → 5′ exonuclease activity produce UV-induced revertants at higher frequency than did their exonuclease proficient counterparts. The data indicates that loss of proofreading activity increases the frequency of UV-induced<unk> s. Detection Fluorescence The effects of neighboring bases and secondary structure to detect the frequency of<unk> s has been investigated in depth using fluorescence. Fluorescently tagged DNA, by means of base analogues, permits one to study the local changes of a DNA sequence. Studies on the effects of the length of the primer strand reveal that an equilibrium mixture of four hybridization conformations was observed when template bases looped-out as a bulge, i.e. a structure flanked on both sides by duplex DNA. In contrast, a double-loop structure with an unusual unstacked DNA conformation at its downstream edge was observed when the extruded bases were positioned at the primer–template junction, showing that misalignments can be modified by neighboring DNA secondary structure. Sequencing A deletion<unk>  alters every codon following it, and can make protein synthesis stop prematurely by forming a stop codon. Sanger sequencing and pyrosequencing are two methods that have been used to detect<unk> s, however, it is likely that data generated will not be of the highest quality. Even still, 1.96 million indels have been identified through Sanger sequencing that do not overlap with other databases. When a<unk>  is observed it is compared against the Human Genome<unk>  Database (HGMD) to determine if the<unk>  has a damaging effect. This is done by looking at four features. First, the ratio between the affected and conserved DNA, second the location of the<unk>  relative to the transcript, third the ratio of conserved and affected amino acids and finally the distance of the indel to the end of the exon. Massively Parallel Sequencing is a newer method that can be used to detect<unk> s. Using this method, up to 17 gigabases can be sequenced at once, as opposed to limited ranges for Sanger sequencing of only about 1 kilobase. Several technologies are available to perform this test and it is being looked at to be used in clinical applications. When testing for different carcinomas, current methods only allow for looking at one gene at a time. Massively Parallel Sequencing can test for a variety of cancer causing<unk> s at once as opposed to several specific tests. An experiment to determine the accuracy of this newer sequencing method tested for 21 genes and had no false positive calls for<unk> s. Diagnosis A US patent (5,958,684) in 1999 by Leeuwen, details the methods and reagents for diagnosis of diseases caused by or associated with a gene having a somatic<unk>  giving rise to a<unk> . The methods include providing a tissue or fluid sample and conducting gene analysis for<unk>  or a protein from this type of<unk> . The nucleotide sequence of the suspected gene is provided from published gene sequences or from cloning and sequencing of the suspect gene. The amino acid sequence encoded by the gene is then predicted. Frequency Despite the rules that govern the genetic code and the various mechanisms present in a cell to ensure the correct transfer of genetic information during the process of DNA replication as well as during translation,<unk> s do occur;<unk>  is not the only type. There are at least two other types of recognized point<unk> s, specifically missense<unk>  and nonsense<unk> . A<unk>  can drastically change the coding capacity (genetic information) of the message. Small insertions or deletions (those less than 20 base pairs) make up 24% of<unk> s that manifest in currently recognized genetic disease.<unk> s are found to be more common in repeat regions of DNA. A reason for this is because of slipping of the polymerase enzyme in repeat regions, allowing for<unk> s to enter the sequence. Experiments can be run to determine the frequency of the<unk>  by adding or removing a pre-set number of nucleotides. Experiments have been run by adding four basepairs, called the +4 experiments, but a team from Emory University looked at the difference in frequency of the<unk>  by both adding and deleting a base pair. It was shown that there was no difference in the frequency between the addition and deletion of a base pair. There is however, a difference in the end result of the protein. Huntington's disease is one of the nine codon reiteration disorders caused by polyglutamine expansion<unk> s that include spino-cerebellar ataxia (SCA) 1, 2, 6, 7 and 3, spinobulbar muscular atrophy and dentatorubal-pallidoluysianatrophy. There may be a link between diseases caused by polyglutamine and polyalanine expansion<unk> s, as<unk> ing of the original SCA3 gene product encoding CAG/polyglutamines to GCA/polyalanines. Ribosomal slippage during translation of the SCA3 protein has been proposed as the mechanism resulting in shifting from the polyglutamine to the polyalanine-encoding frame. A dinucleotide deletion or single nucleotide insertion within the polyglutamine tract of huntingtin exon 1 would shift the CAG, polyglutamineen coding frame by +1 (+1<unk>  to the GCA, polyalanine-encoding frame and introduce a novel epitope to the C terminus of Htt exon 1 (APAAAPAATRPGCG).
Frameshift mutation
Exon skipping
Exon shuffling
Deletion 
Fusion transcript
Efference copy
Osseoincorporation
Copy number variation