Expansion of tandem repeats and oligomer clustering in coding and noncoding DNA sequences

We review recent studies of distribution of dimeric tandem repeats and shor t oligomer clustering in DNA sequences. We find that distribution of dimeri c tandem repeats in coding DNA is exponential, while in noncoding DNA it of ten has long power-law tails. We explain this phenomenon using mutation mod els based on random multiplicative processes. We also develop a clustering measure based on percolation theory that quantifies the degree of clusterin g of short oligomers. We find that mono-, di-, and tetramers cluster more i n noncoding DNA than in coding DNA. However trimers have some degree of clu stering in coding DNA and noncoding DNA. We relate this phenomena to modes of tandem repeat expansion. (C) 1999 Elsevier Science B.V. All rights reser ved.