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Monday Seminar: March 5, 2007 4pm in Biosciences West (map), Room 301"Locating the target of selective sweeps: theory and practice, with lessons from Drosophila" Chip is a leader in population genetics and an excellent speaker. If you are interested in meeting with him please send an email to Michael Nachman (nachman@u.arizona.edu) indicating your availability on Monday and Tuesday until 11 am. There will be a dinner party for Chip at Michael Nachman's house (2046 E 4th St) Monday at 6, and everyone is welcome. |
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Talk Abstract: Efforts to detect targets of recent positive selection (“selective sweeps”) in the genome frequently involve an initial screen of a region of the genome at a low density of markers (either SNPs or microsatellites), followed by a denser screen in the region flanking markers that show reduced or skewed variation relative to that predicted by an equilibrium neutral model or relative to “background” variation in the genome. Direct sequencing is often then used to attempt to localize the gene/variation that was the target of the selective sweep. I will discuss how non-equilibrium demography seriously complicates the effort to initially detect departures due to natural selection, as well as subsequent efforts to localize the selective target. I will discuss a Goodness of Fit test that, when combined with Kim and Stephan’s composite likelihood method for detecting and localizing sweeps, does reasonably well at distinguishing positive selection from many demographic perturbations. I will also provide examples from our relatively dense microsatellite screen of 400 kb of the X-chromosome in Drosophila melanogaster for both African and non-African population samples with follow-up sequencing that reveal departures from an equilibrium neutral model due to positive selection on synonymous, nonsynonymous, and regulatory variants, to demography alone, and to demographic amplification of ancestral sweeps. I will also summarize several case studies that illustrate just how pervasive, subtle, and sometimes elusive, natural selection can be. And of course, for Michael, one is a case of positive selection for pigmentation in D. melanogaster. |
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