Evidence on DNA slippage step-length distribution

A simple model based on a master equation is constructed in order to reveal the details of the mutational events modifying simple sequence repeats in the human genome, A database of simple repeats together with their flanking sequences comprising approximately 10⁵ entries from all 24 human chromosomes was constructed. By aligning the pairs of fragments of sequences containing the repeat elements, the matrices that count the number of slippage events were evaluated. The counts were then used as a target to be reproduced by our theoretical model, in which the elongation and shortening of the repeats proceed through a mechanism in which the step lengths exhibit a decaying distribution in the form of an inverse power law rather than through one nucleotide extension or deletion, which was the most frequent supposition in previous studies.