Abundance and length of simple repeats in vertebrate genomes are determined by their structural properties.

Microsatellites are abundant in vertebrate genomes, but their sequence representation and length distributions vary greatly within each family of repeats (e.g., tetranucleotides).

The involvement of non-B DNA structures in gross chromosomal rearrangements.

Non-B DNA conformations adopted by certain types of DNA sequences promote genetic instabilities, especially gross rearrangements including translocations. We conclude the following: (a) slipped (hairpin) structures, cruciforms, triplexes, tetraplexes and i-motifs, and left-handed Z-DNA are formed in chromosomes and elicit profound genetic consequences via recombination-repair, (b) repeating sequences, probably in their non-B conformations, cause gross genomic rearrangements (translocations, deletions, insertions, inversions, and duplications), and (c) these rearrangements are the genetic basis for numerous human diseases including polycystic kidney disease, adrenoleukodystrophy, follicular lymphomas, and spermatogenic failure.

Non-B DNA conformations formed by long repeating tracts of myotonic dystrophy type 1, myotonic dystrophy type 2, and Friedreich's ataxia genes, not the sequences per se, promote mutagenesis in flanking regions.

The expansions of long repeating tracts of CTG.CAG, CCTG.CAGG, and GAA.

The myotonic dystrophy type 1 triplet repeat sequence induces gross deletions and inversions.

The capacity of (CTG.CAG)n and (GAA.TTC)n repeat tracts in plasmids to induce mutations in DNA flanking regions was evaluated in Escherichia coli.

Breakpoints of gross deletions coincide with non-B DNA conformations.

Genomic rearrangements are a frequent source of instability, but the mechanisms involved are poorly understood. A 2.5-kbp poly(purine.

Long CTG.CAG repeats from myotonic dystrophy are preferred sites for intermolecular recombination.

Homologous recombination was shown to enable the expansion of CTG.CAG repeat sequences. Other prior investigations revealed the involvement of replication and DNA repair in these genetic instabilities.