When a population's genetic makeup is changed randomly, it is called genetic drift. In natural selection, environment is the selection agent but in genetic drift, chance is the selection agent (Nowicki 305). Since genetic drift is controlled by chance, smaller populations are more prone to being affected by genetic drift. If someone flips a coin six times, the results will not always be split between heads and tails at fifty percent. Although if someone flips a coin one thousand times, the percentage of heads and tails will be closer to fifty percent (Small Population Side Effects). Genetic drift can start from things called the bottleneck effect or the founder effect (Nowicki 336).
The bottleneck effect can make a population small enough for genetic drift to affect it. Nowicki writes, "The bottleneck effect is genetic drift that occurs after an event greatly reduces the size of a population." (Nowicki 336). These events could include natural disasters like earthquakes, or it could be overhunting. In the 1890's northern elephant seals were massively hunted, much less than the southern elephant seals. This hunting brought the northern elephant seal count down to approximately 20 seals. Even now, you can see the effects from that occurrence of the bottleneck effect. The southern elephant seals, who were not hunted as much, are extremely more genetically diverse than the northern elephant seals. After the event, some of the alleles become fixe...
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"Genetic Drift of HIV Populations in Culture." Yegor Voronin. PLoS Genetics. Voronin et al, 20 Mar. 2009. Web. 6 Mar. 2014.
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Nowicki, Stephen. McDougal Littell Biology. Canada: McDougal Littell, 2008. Print.
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