Indel

Indel is a molecular biology term for the insertion or the deletion of bases in the DNA of an organism. It has slightly different definitions between its use in evolutionary studies and its use in germ-line and somatic mutation studies.

In coding regions of the genome, unless the length of an indel is a multiple of 3, it will produce a frameshift mutation. For example, a common microindel which results in a frameshift causes Bloom syndrome in the Jewish or Japanese population. Indels can be contrasted with a point mutation. An indel inserts and deletes nucleotides from a sequence, while a point mutation is a form of substitution that replaces one of the nucleotides without changing the overall number in the DNA. Indels can also be contrasted with Tandem Base Mutations (TBM), which may result from fundamentally different mechanisms. A TBM is defined as a substitution at adjacent nucleotides (primarily substitutions at two adjacent nucleotides, but substitutions at three adjacent nucleotides have been observed.

"Indels", as defined as either an insertion or deletion, can be used as genetic markers in natural populations, especially in phylogenetic studies. It has been shown that genomic regions with multiple indels can also be used for species-identification procedures.

An indel change of a single DNA base encoding part of an mRNA results in a "frameshift" when translating the mRNA and perhaps reading on to an inappropriate (premature) stop codon in a different frame. Indels that are not multiples of 3 are particularly uncommon in coding regions but relatively common in non-coding regions. There are approximately 192-280 frameshifting indels in each person. Note, however, the absolute rate of indels in most known genomes, including humans, tends to be markedly lower than base substitutions, except near highly repetitive regions, including homopolymers and microsatellites.

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