Our novel Python-based tool EVANGELIST allows the visualization of GC and repeats percentages along chromosomes in sequenced genomes and has enabled us to perform quantitative large-scale analyses on the chromosome level in fish and other vertebrates. This is a different approach from the prevailing analyses, i.e., analyses of GC% in the coding sequences that make up not more than 2% in human. We identified GC content (GC%) elevations in microchromosomes in ancient fish lineages similar to avian microchromosomes and a large variability in the relationship between the chromosome size and their GC% across fish lineages. This raises the question as to what extent does the chromosome size drive GC% as posited by the currently accepted explanation based on the recombination rate. We ascribe the differences found across fishes to varying GC% of repetitive sequences. Generally, our results suggest that the GC% of repeats and proportion of repeats are independent of the chromosome size. This leaves an open space for another mechanism driving the GC evolution in vertebrates.

Department of Bioinformatics Wissenschaftszentrum Weihenstephan Technische Universität München 85354 Freising Germany

Department of Biological and Environmental Sciences Samford University Birmingham AL 35226 USA

Faculty of Science University of Hradec Kralove 500 03 Hradec Kralove Czech Republic

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Abandoning the Isochore Theory Can Help Explain Genome Compositional Organization in Fish

Advances in Vertebrate (Cyto)Genomics Shed New Light on Fish Compositional Genome Evolution

GC and Repeats Profiling along Chromosomes-The Future of Fish Compositional Cytogenomics

Present and Future Salmonid Cytogenetics