ABSTRACT
Other than virus genomes, the first genomes of cellular organisms began to be published about two decades ago. However, the initial genomes were primarily descriptive, covering the contents of a single genome. Once a few bacterial genomes were completed, comparisons were made among the genomes outlining the similarities and differences between the genomes. Once the first archaeal genome (Methanocaldococcus jannaschii) and the first eukaryotic genomes were published (Saccharomyces cerevisiae and Caenorhabditis elegans), the genomes of the three large domains of life were compared for the first time, which initiated the field of comparative genomics. However, the number of genomes was still too small for phylogenetic reconstructions, and therefore, for a few more years, phylogenetics consisted of the analyses of one or a few gene regions from sets of organisms.
