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Evolutionary Biology/Phylogeny


The basic context in which evolutionary biology works is phylogeny, a system of classification based on evolutionary relationships rather than phenotypic similarity. The central tenet of evolution is that all life is derived from a single common ancestor, and all life is therefore related. The process by which living things have diverged to the staggering diversity on this world is through the divergence of populations into separate species, which in turn give rise to more distant cousins through time.

We express the relationships among groups of organisms through diagrams called cladograms. If the common ancestor is known and included in the depiction and the depiction includes an axis of time, it is referred to as an evolutionary tree.

Evolutionary Biology/Primary endosymbiosis

Definition Primary endosymbiosis is the process which involves the engulfment of a prokaryote by another living cell. The engulfed organism may be used as an advantage, supplying the larger cell with its products. For example, if a eukaryotic cell engulfs a photosynthetic alga cell, the eukaryotic cell can then use the products of the alga and become an autotrophic organism. Either cell can be affected if one of the cells dies. If the larger cell dies the engulfed cell may leave the remains of the larger cell in order to survive. If the originally engulfed cell dies instead, the larger organism will continue to live. Following primary endosymbiosis, the larger cell may be engulfed itself. This is the process of secondary endosymbiosis. Scientists believe that endosymbiosis has lead to the creation and evolution of both cholroplasts and mitochondria. This theory is called the Endosymbiotic theory. Endoscopic-Theary Endosymbiotic Theory: Scientists believe that chloroplasts and mitochondria were created from the process of endosymbiosis.

Evolutionary Biology/Secondary endosymbiosis

Definition A process in eukaryotic evolution in which a heterotrophic eukaryotic cell engulfed a photosynthetic eukaryotic cell which survived in a symbiotic relationship inside the heterotrophic cell from primary endosymbiosis. Secondary endosymbiosis is when a living cell engulfs another eukaryote cell that has already undergone primary endosymbiosis. It has happened often enough that it has lead to genetic diversity among the organisms on Earth. Though it undergoes the same process of primary endosymbiosis, the cell that becomes engulfed now becomes very dependent on the larger cell. Unlike primary endosymbiosis, the engulfed cell cannot leave the larger cell and return to its original state. The engulfed primary endosymbiosis cell now has a double phospholipid bilayer. The bilayer consists of its original outer membrane and the membrane of the cell it engulfed in primary endosymbiosis. This evidence of a phospholipid bilayer also encourages that both mitochondria and chloroplasts originated from endosymbiosis.
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