Fractal Genomics of SOD1 Evolution

Abstract

To understand the fundamental processes of gene evolution such as the impact of point mutations and segmental duplications on statistical topography, Superoxide Dismutase-1 (SOD1) orthologous sequences (n=50) were studied. These demonstrated scale invariant self-similarity patterns and long-range correlations (LRC) indicating fractal organization. Phylogenetic hierarchies changed when SOD1 orthologs were grouped according to fractal measures, indicating statistical topographies can be used to study gene evolution. Sliding window k-mer analysis showed that majority of k-mers across all SOD1 orthologs were unique, with very few duplications. Orthologs from simpler species contributed minimally (<1% of k-mers) to more complex species. Both simple and complex random processes failed to produce significant matching k-mer sequences for SOD1 orthologs. Point mutations causing amyotrophic lateral sclerosis did not impact the fractal organization of human SOD1. Hence, SOD1 did not evolve by a patchwork of repetitive sequences modified by point mutations. Instead, this study proposes that SOD1 gene sequences evolved by regulated interweaving of unique oligomer sequences that led to LRC, signifying convergent evolution. Summary StatementSOD1 has long-range correlations which resulted not from point mutations, segmental duplications or patching together sequences from simpler organisms. Instead, SOD1 underwent convergent evolution by repeated unique sequence assemblies.