slatkin5Answers - Bio 1B, Spring, 2007, Evolution section 1...

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Bio 1B, Spring, 2007, Evolution section 1 of 3 Updated 3/2/07 9:49 AM Lecture 5 5 Genetic drift and gene flow Reading: 7 th edition 460-462, 506; 6 th edition 450-452,503. Allele frequencies change because of genetic drift Genetic drift occurs because populations are not infinitely large On average, allele frequencies do not change after random mating. But in any one population, allele frequencies will change slightly each generation because the population size is finite. The rate of change in allele frequency because of genetic drift is small in large populations and larger in small populations. Bottlenecks and founder events A bottleneck in population size and a founder event both affect allele frequencies. A bottleneck is a reduction in size of an existing population while a founder event is the establishment of a new population of smaller size. Both cause more rapid changes in allele frequencies than would occur in a large stable population. Extreme bottlenecks and founder events lead to the loss of many alleles along with the increase in frequency of a few alleles. Cheetahs probably experienced an extreme bottleneck in size. There are so few genetic differences between individuals that skin can be successfully grafted between unrelated individuals, something that is impossible in other mammals. Founder events are important for the study of human genetic diseases Isolated populations founded by a few individuals may have some genetic diseases in high frequency that are rare elsewhere. Huntington’s disease (HD) is a late-onset dominant lethal condition. In the US
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slatkin5Answers - Bio 1B, Spring, 2007, Evolution section 1...

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