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Population bottleneck followed by recovery or extinction. A population bottleneck or genetic bottleneck is a sharp reduction in the size of a population due to environmental events such as famines, earthquakes, floods, fires, disease, and droughts; or human activities such as genocide, speciocide, widespread violence or intentional culling.
The impact of a population bottleneck can be sustained, even when the bottleneck is caused by a one-time event such as a natural catastrophe. An interesting example of a bottleneck causing unusual genetic distribution is the relatively high proportion of individuals with total rod cell color blindness ( achromatopsia ) on Pingelap atoll in ...
Another possible cause of genetic divergence is the bottleneck effect. The bottleneck effect is when an event, such as a natural disaster, causes a large portion of the population to die. By chance, certain genetic patterns will be overrepresented in the remaining population, which is similar to what happens with the founder effect. [4]
A bottleneck can reduce or eliminate genetic variation from a population. Further drift events after the bottleneck event can also reduce the population's genetic diversity. The lack of diversity created can make the population at risk to other selective pressures. [36] A common example of a population bottleneck is the Northern elephant seal ...
Cells that do not proceed through this checkpoint remain in the G0 stage and do not replicate their DNA. [citation needed] Once the DNA has gone through the "G1/S" test, it can only be copied once in every cell cycle. When the Mcm complex moves away from the origin, the pre-replication complex is dismantled.
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Phototaxis is a kind of taxis, or locomotory movement, that occurs when a whole organism moves towards or away from a stimulus of light. [106] This is advantageous for phototrophic organisms as they can orient themselves most efficiently to receive light for photosynthesis .
When these cells have accomplished these tasks, the immune system clears them away. This phenomenon is termed acute senescence. [30] Senescence of hepatic stellate cells could prevent progression of liver fibrosis, although this has not been implemented as a therapy, and would carry the risk of hepatic dysfunction. [74]