Introduction to Genetic Analysis 638

Introduction to - zygous but the pattern of frequencies of the alleles is very different in the two Even a new mutation that is slightly favorable

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Unformatted text preview: zygous, but the pattern of frequencies of the alleles is very different in the two. Even a new mutation that is slightly favorable selec- tively will usually be lost in the first few generations after it appears in the population, a victim of genetic drift. If a new mutation has a selective advantage of s in the het- erozygote in which it appears, then the chance is only 2 s that the mutation will ever succeed in taking over the population. So a mutation that is 1 percent better in fit- ness than the standard allele in the population will be lost 98 percent of the time by genetic drift. It is even possible for a very slightly deleterious mutation to rise in fre- quency and become fixed in a population by drift. will sweep through the population and become fixed. This event has the probability of 1/2 N . In the absence of selection, then, the history of a population looks like Fig- ure 19-13. For some period of time, it is homozygous; then a new mutation appears. In most cases, the new mutant allele will be lost immediately or very soon after it appears. Occasionally, however, a new mutant allele drifts through the population, and the population be- comes homozygous for the new allele. The process then begins again....
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This note was uploaded on 01/10/2011 for the course BIOL BIOL taught by Professor Johnson during the Spring '08 term at Aberystwyth University.

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