Examining the Coevolution of Genome Sizes, GC contents, and Gene Direction

Genome variation is essential for the evolution of living organisms. I analyzed several aspects of the reference genomes and completed genomes available in NCBI (www.ncbi.nlm.nih.gov) and various other public databases. In this presentation, I will describe the variation of genome size, chromosome size, base composition, and gene direction on chromosomes in each kingdom and various subkingdoms of living organisms. The genome size variation was found to be greater in Gram-positive bacteria and archaeans than in Gram-negative bacteria. The largest and smallest genomes in bacteria were in 66 fold difference in size. Archaeans and bacteria showed far greater within-subkingdom variation of GC content (i.e., C+G content) than plants and animals. The positive correlation between genome size and GC content was mainly in Actinobacteria and Proteobacteria, but not in most other bacteria. Species-level GC contents and genome sizes did not show significant correlation in either animals or plants. Genes were predominantly aligned in the same direction on chromosomes in prokaryotes but facing predominantly in the opposite directions from each other in fungi and Chlorophyta (having larger genome sizes than prokaryotes). The driving force difference in the genome size variation between species groups, the mechanisms underlying gene direction on chromosomes, the relationship between genome size and GC content, and the coevolution between genome size and gene direction will be discussed.