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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 locus in this population has two alleles, A and a, that occur with initial frequencies f 0 (A) = p and f 0 (a) = q, respectively. [ note 1 ] The allele frequencies at each generation are obtained by pooling together the alleles from each genotype of the same generation according to the expected contribution from the homozygote and ...
The level of gene flow among populations can be estimated by observing the dispersal of individuals and recording their reproductive success. [4] [11] This direct method is only suitable for some types of organisms, more often indirect methods are used that infer gene flow by comparing allele frequencies among population samples.
[35] [36] If environmental effects are related to a variant that exists in only one specific region (for example, a pollutant is found in only one city), it may not be possible to correct for this population structure effect at all. [29]
Lines are drawn from each circle to the circles in the other column(s), and the thickness of the connecting line is proportional to the frequency that the two genotypes occur together. Linkage disequilibrium is seen through the number of line crossings in the diagram, where a greater number of line crossings indicates a low linkage ...
Similar to the bottleneck effect, the founder's effect can also cause allele fixation. The founder effect occurs when a small founding population is moved to a new area and propagates the future population. This can be seen in the Alces alces moose population in Newfoundland, Canada. Moose are not native to Newfoundland, and in 1878 and 1904 ...