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4.3.doc

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Department
Biology
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BIOL 1001
Professor
Tamara Kelly

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4.3 – Genetic Drift ∙ Natural Selection is not random, and is directed by the environment and results in adaptation ∙ Genetic drift, is undirected and random ∙ Genetic Drift; is defined as any change in allele frequencies in a population that is due to chance o It causes allele frequencies to drift up and down randomly over time o When drift occurs, allele frequencies change due to blind luck known as sampling error o Drift occurs in every population, in every generation Simulation Studies of Genetic Drift ∙ Imagine a couple marooned on a deserted island  ∙ Suppose that gene A, the wife’s genotype is ATAH and the husbands is also ATAH, the couple  produce 5 children ∙ To simulate which sperm and which egg happen to combine to produce each of the 5 offspring,  you can flip a coin for each sperm and each egg, with tails standing for allele AT and heads is AH  ∙ When the parents die, there are a total of 10 alleles in the population ∙ Note that the allele frequencies have changed, in this generation 6 of the 10 alleles (60%) are AH  and 40% are AT ∙ Evolution – a change in allele frequencies in a population occurred due to genetic drift ∙ Genetic drift is random with respect to fitness ∙ Genetic drift is most pronounced in small populations  ∙ Over time, genetic drift can lead to the random loss or fixation of alleles Experimental studies of Genetic Drift ∙ Genetic marker – a specific allele that causes distinctive phenotypes ∙ As predicted, genetic drift decreased genetic variation within populations and increased genetic  differences between populatio
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