Repeated regions in mitochondrial genomes: distribution, origin and evolutionary significance.

All complete or nearly complete mitochondrial genomes of Metazoa (2819) have been subject to bioinformatic analysis to investigate the distribution and features of repeated and palindromic sequences. Repeats are ubiquitous, with 29.9% of genomes containing at least one and 1.95% of total genome length being repeated. Repeat boundaries were tested for the presence of secondary structure motifs, consensus sequences or small repeats, features generally reported as associated with duplications. No significant relationship was detected, suggesting the non ubiquitousness of such features. A mechanism related to gene conversion is proposed to explain the origin of small interspersed repeats.