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The original theory by Lynn Margulis proposed an additional preliminary merger, but this is poorly supported and not now generally believed. [1] Symbiogenesis (endosymbiotic theory, or serial endosymbiotic theory [2]) is the leading evolutionary theory of the origin of eukaryotic cells from prokaryotic organisms. [3]
An overview of the endosymbiosis theory of eukaryote origin (symbiogenesis). Symbiogenesis theory holds that eukaryotes evolved via absorbing prokaryotes. Typically, one organism envelopes a bacterium and the two evolve a mutualistic relationship. The absorbed bacteria (the endosymbiont) eventually lives exclusively within the host cells.
They are thought to be vestiges of red and green algal nuclei that were engulfed by a larger eukaryote. Because the nucleomorph lies between two sets of membranes, nucleomorphs support the endosymbiotic theory and are evidence that the plastids containing them are complex plastids. Having two sets of membranes indicate that the plastid, a ...
Endogenosymbiosis is an evolutionary process, proposed by the evolutionary and environmental biologist Roberto Cazzolla Gatti, in which "gene carriers" (viruses, retroviruses and bacteriophages) and symbiotic prokaryotic cells (bacteria or archaea) could share parts or all of their genomes in an endogenous symbiotic relationship with their hosts.
This theory is called the endosymbiotic theory. In the cells of extant organisms, the vast majority of the proteins in the mitochondria (numbering approximately 1500 different types in mammals ) are coded by nuclear DNA , but the genes for some, if not most, of them are thought to be of bacterial origin, having been transferred to the ...
Evidence for primary endosymbiosis includes the presence of a double membrane around the chloroplasts; one membrane belonged to the bacterium, and the other to the eukaryote that captured it. Over time, many genes from the chloroplast have been transferred to the nucleus of the host cell through endosymbiotic gene transfer (EGT).
This formed the first experimental evidence for the symbiogenesis theory. [8] The endosymbiosis theory of organogenesis became widely accepted in the early 1980s, after the genetic material of mitochondria and chloroplasts had been found to be significantly different from that of the symbiont's nuclear DNA .
Secondary endosymbiosis results in the engulfment of an organism that has already performed primary endosymbiosis. Thus, four plasma membranes are formed. The first originating from the cyanobacteria, the second from the eukaryote that engulfed the cyanobacteria, and the third from the eukaryote who engulfed the primary endosymbiotic eukaryote. [11]