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Unformatted text preview: Genetic Drift
genetic drift random change in gene frequency due to chance. With a large population chance factors have little effect on gene frequencies. But with small populations, chance factors may produce random changes in gene frequency. Example: If we flip a quarter, we expect 50% heads and 50% tails. If we flip the coin 1000 times, we get results very close to the 50:50 ratio. But, if we flip the quarter only 4 times, we may get 3 heads and 1 tail or all heads or all tails. When the sample size is small, or in this case flips, then sampling error can be large. All genetic drift arises from such sampling error. Causes Genetic drift arises when population size remains continuously small over many generations. All genetic drift arises from sampling error, but there are several ways in which sampling error occurs in natural populations. 1.Founder effect: occurs when a population is initially established by a small number of individuals. Although the population may grow in size and consist of a large number of individuals, the gene pool of the population is derived from the genes present in the original founders. 2.Bottleneck effect: occurs when a population is drastically reduced in size. During such a population reduction, some genes may be lost from the gene pool as a result of chance (Bottleneck effect may be viewed as a type of founder effect since the population is refounded by those few individuals that survive the reduction). ...
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- Spring '08