Читать книгу Algorithms in Bioinformatics - Paul A. Gagniuc - Страница 41

The last universal common ancestor (LUCA) was likely a population of unicellular organisms that led to the emergence of two domains in prokaryotes: Bacteria and Archaea. It seems that LUCA were complex unicellular organisms and not the immediate descendants of primeval cells. Rumor “has it” that prokaryotes are the descendants of LUCA by reductive evolution [98]. Nevertheless, evidence shows that about 2 billion years ago, eukaryotic cells may have evolved from a merger between the two prokaryotic domains. Endosymbiosis theory suggests a scenario in which an archaeal cell engulfed a bacterial cell. This kind of merger was repeated independently many times and eventually evolved to form all the membrane-bound organelles, including the mitochondria and chloroplasts. The last eukaryotic common ancestor (LECA) was likely a population of unicellular organisms that eventually (i.e. within 300 million years of LECA) led to a diversification of eukaryotes in supergroups (around 1.5–2 billion years ago) [99, 100]. Today, existing prokaryotic groups reveal the intermediate steps in the eukaryotic-cell evolution [101]. Moreover, complex archaea that bridge the gap between prokaryotes and eukaryotes have been found [102].