Richard Koehn, ofthe State University of New York, Stony

Chapter 0, Problem 7

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Richard Koehn, ofthe State University of New York, Stony Brook, and Thomas Hilbish, ofthe University of South Carolina, studied genetic Y-Jriation in the marine mussel Mytillls edulis around umg Island, New York. They measured the frequency of a particular allele (lnp94) for an enzyme involved in regulating the mussel's internal salt-water balance. The resmrchers presented their data as a series ofpie charts linked to sampling sites within long Island Sound, where the salinity is highly variable, and along the coast ofthe open ocean, where salinity is constant: Create a data table for the 11 sampling sites by estimating thefrequency oflap94 from the pie charts. {Hint: Think of each piechart as a dock face to help you estimate the proportion oftheshaded area.) Then graph the frequencies for sites 1-8 to showhow the frequency ofthis allele changes with increasing salinityin Long Island Sound (from southwest to northeast). How dothe data from sites 9-11 compare with the data from the siteswithin the Sound?Construct a hypothesis that explains the patterns you observein the data and that accounts for the following observations:(I) the lap94 allele helps mussels maintain osmotic balancein water with a high salt concentration but is costiyto use in lesssalty water; and (2) mussels produce larvae that can disperselong distances before they settle on rocks and grow into adults.