Читать книгу Algorithms in Bioinformatics - Paul A. Gagniuc - Страница 56

There is no direct correlation between the genome size of a species and the complexity of its phenotype. In any case, the intellectual curiosity regarding the size of genomes still remains. Determination of genome size based on DNA sequencing data is one of the most accurate methods to date. To observe the lack of correlation between genome size and phenotype, upper-bound extremes can be considered here. As expected in an intuitive manner, eukaryotes show the largest genomes. In animals, the amphibian Ambystoma mexicanum (the Mexican Axolotl) shows the largest (sequenced) genome observed in nature to date. A. mexicanum shows a genome size of 32 396 Mbp (32 Gb) and a physical length that can reach up to 30 cm [166]. In plants, the record is held by Pinus lambertiana (27 603 Mbp) and Sequoia sempervirens (26 537 Mbp). P. lambertiana is the tallest and most massive pine tree [167, 168]. S. sempervirens species includes the tallest living trees on Earth (115.5 m in height or 379 ft) [169]. Among the prokaryotes, Minicystis rosea and Sorangium cellulosum So0157-2 show the largest genomes. The bacterial genome of M. rosea contains 16 Mbp of DNA (GC%: 69.1) and shows the maximum genome size found in prokaryotes [170]. Secondary to this species is the bacterial genome of S. cellulosum So0157-2, with 14.78 Mbp of DNA (GC%: 72.1) [171]. As discussed in the previous chapter, endosymbiosis challenges the notion of the smallest genome necessary for life. The smallest prokaryotic genomes were found in different obligate symbionts. One such case is Nasuia deltocephalinicola with a genome of 112 kbp (0.11 Mbp) [172, 173]. The eukaryotes with the smallest nuclear genome necessary for life are found in the kingdom of fungi. The spore-forming unicellular parasite Encephalitozoon intestinalis shows a genome size of ∼2.3 Mbp and a total of 1.8k protein-coding genes [174]. Nonetheless, the smallest free-living eukaryote is Ostreococcus tauri, a marine green alga with a diameter of about 0.8 μm and a genome size of 12.6 Mbp (8.2k protein-coding genes) [175].