Prep 8 – Due Tuesday, March 8 at class time
Reading/Viewing
Please re-read section 6.6 (Selection: Winning and Losing) focusing specifically on predicting allele frequencies after selection and on what kinds of selection reduce genetic variability and what kinds tend to maintain multiple alleles in the population.
Finish reading chapter 8 (Natural Selection: Empirical Studies in the Wild)
Hetero zygote advantage and beyond
We have seen in class that the most common result of natural selection is a selective sweep; the favored allele is swept to fixation while the less favored allele becomes extinct in the population. Please review (in writing) what we have said in class about why this happens, what determines how fast it happens, and under what circumstances this does or does not happen.
Now, as you read the chapter think about the fact there is an amazing amount of genetic diversity at many loci despite the fact that natural selection operates all the time. How can this be true? Describe in detail the different mechanisms described in the chapter for maintaining genetic diversity in the presence of natural selection.
Use examples from chapter 8 to discuss when diversity is maintained under selection and when it is lost. Use the following concepts as a guide: antagonistic pleiotropy, selection for dominant alleles, heterozygote advantage (overdominance), mutation-selection balance, negative frequency-dependent selection, character displacement, geographic differences in selection pressures, selective sweep. Make sure you explain the meaning of all of these terms and give details about how each example illustrates them. If you cannot find examples in the book, do a web search. Do human influences on natural populations tend to increase or decrease diversity? Why and how?
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