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Mutations are permanent changes in the DNA. When these changes occur in a DNA sequence coding for a protein, they can induce several consequences. First, they can cause the replacement of an aminoacid by another, these are called missense mutations. Next, they can replace an aminoacid by a "stop" instruction causing the interruption of the protein, these are called non-sense mutations. The third type of mutations are deletions or insertions. Deletions are loss of DNA (from 1 base to several thousand). Insertions are gain of DNA (from 1 base to several thousand). In these two latter cases (deletions and insertions) the result for the coding sequence is called a "frameshift", causing the premature occurence of a "stop" instruction interrupting the synthesis of the protein.
Let's take the following sentence that could be the coding sequence for a protein (this sentence has a meaning) :
SHE ATE THE PIE
A missense mutation will produce the following effect (missense mutations sometime allow to preserve a partial meaning, that is a partial function in the case of a protein). In the example below, the modification affects the 10th letter. It is the replacement of the letter "P" by the letter "T". This mutation will be written P10T (replacement of the P in 10th position by a T). The same rules apply for mutations in genes (aminoacid normally present, its position in the protein, the new aminoacid). T158M = threonine (T) at position 158 is replaced by a methionine (M).
SHE ATE THE TIE
A nonsense mutation will have the following effect. The meaning of the sentence is totally lost. The "stop" signals are coded using "*" or the letter "X". The same way of naming mutations is used. In our example (below), the "stop" appears at position 6 to replace the letter "E", we will write E6X. In the case of human genes, an example could be R268X : arginine (R) at position 268 replaced by a stop (X).
SHE AT*
An insertion will have the following effect. Again, the meaning of the sentence is totally lost. The instructions in the DNA (genes coding for proteins) are read by groups of 3 "letters" (3 nucleotides). An insertion will modify these groups of 3 and the meaning will be lost. In our example below, we made an insertion after the 4th letter. We inserted the "C" letter. We will write 4ins1 or 4insC. In genes, it will be for example : 806insA meaning that the nucleotide A was inserted after nucleotide at position 806. If two nucleotides are inserted, it could be 806insAT. If long stretches of DNA are inserted, than the number of nucleotides inserted can be used : 806ins45 for an insertion of 45 nucleotides after position 806.
SHE ACT ETH EPI E
A deletion will have the following effect. Again, the meaning of the sentence is totally lost. The instructions in the DNA (genes coding for proteins) are read by groups of 3 "letters" (3 nucleotides). A deletion will modify these groups of 3 and the meaning will be lost. In our example below, we made a deletion after the 4th letter. We deleted the "T" letter. We will write 4del1 or 4delT. In genes, it will be for example : 1174delG meaning that the nucleotide G was deleted after nucleotide at position 1174. If two nucleotides are deleted, it could be 1174insGC. If long stretches of DNA are deleted, than the number of nucleotides deleted can be used : 1174del54 for a deletion of 54 nucleotides after position 1174.
SHE AET HEP IE