Trinucleotide Repeats and Expansion
Trinucleotide repeats are apparent in a number of loci in the human genome. They have been found in introns, exons and 5' or 3' UTR's. They consist of a pattern of three nucleotides (e.g. CGG) which is repeated a number of times. During meiosis, unstable repeats can undergo triplet expansion (see later section); in this case, the germ cells produced have a greater number of repeats than are found in the somatic tissues.
The mechanism behind the expansion of the triplet repeats is not well understood. One hypothesis is that the increasing number of repeats influence the overall shape of the DNA, which can have an effect on its interaction with DNA polymerase and thus the expression of the gene.
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