SSR (simple sequence repeats) are ubiquitously abundant in genomes. In organellar mitochondrial genome of animals, its distribution, size dynamics and effectiveness for phylogenetic relationship have not been understood. Present investigation reveals organisation of SSR in genic and intergenic region, its length and repeat motif dynamics, extent of conservation of flanking regions, appropriateness of these SSR data in establishing phylogenetic relationship. Contrary to eukaryotic nuclear abundance of SSR in non-coding region, we found abundance in coding region. Like nuclear SSR, most hyper mutable repeats were found in non coding region having di nucleotide motifs of mitochondrial genome but contrary to human having high mutable tetra repeats in case of mitochondrial genomes this was found to be with tri-motif repeats. SSR of mitochondrial genomes also show cyclical expansion and shrinkage in pattern of SHM (simple harmonic motion) with respect to time its non- linear thus not appropriate for phylogenetic analysis though the flanking regions of these SSR also conserved like nuclear SSR.
Keywords: Cyclical expansion; Distribution; Dynamics; Phylogenetic relationship; SHM; SSRs.