[Size and organization of species genomes]
2008
Savchenko, V.K., National Academy of Sciences (Belarus). Institute of Genetics and Cytology
The size of species genome is defined as the quantity of DNA in one chromosome procaryote or eucariot gamete. Its value is constant for each species but varies significantly within the frames of taxonomic groups from 10E3 up to 10E11 nucleotide base pairs. The genome size grew up with in course of evolution and earlier emerged prokaryotic species had smaller size of genome in comparison the later emerged eukaryotic species. The prokaryotic genomes include about 80 - 90% of coding sequences and there is the direct positive relation between species genome size and number of genes. In accordance with research results, there is no direct relation between species genome size, haploid set of chromosomes and complexity of organisms. The eubacterial genes include only coding sequences without introns and many of them are associated into operons. Operon includes several functionally connected genes with common promoter. The archaea genomes have introns in their tRNA genes and which are closer by genome organisation to eukaryotes than eubacteria. The eukaryotic species genome organisation differs significantly both in eubacteria and in archaebacteria. Eukaryotes have nucleus with the varied number of linear chromosomes which is associated with the haploid genomes of mitochondria and chloroplasts in green plant species. The processes of transcription and translation are separated in eukaryotes. The first one takes place in the nucleus whiles the second one - in the cytoplasm. Eukaryotic genomes carry abundant repeats, transposons, retroviruses and other junk DNA increasing their size
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