Chapter 23, Problem 7TYU

SCIENTIFIC INQUIRY • INTERPRET THE DATA Researchers studied genetic variation in the marine mussel Mytilus edulis around long Island, New York. They measured the frequency of a particular allele (lap⁹⁴) for an enzyme involved in regulating the mussel's internal saltwater balance. The researchers presented their data as a series of pie Charts linked to sampling sites within Long Island Sound, where the salinity is highly variable, and along the coast of the open ocean, where salinity is constant. (a) Create a data table for the 11 sampling sites by estimating the frequency of lap⁹⁴ from the pie Charts. (Hint: Think of each pie chart as a clock face to help you estimate the proportion of the shaded area.) (b) Graph the frequencies for sites 1-8 to show how the frequency of this allele changes with increasing salinity in Long Island Sound (from southwest to northeast). Evaluate how the data from sites 9-11 compare with the data from the sites within the Sound. (c) Considering the various

mechanisms that can alter allele frequency, construct a hypothesis that explains the patterns you observe in the data and that accounts for the following observations: (1) The lap⁹⁴ allele helps mussels maintain osmotic balance in water with a high salt concentration but is costly to use in less salty water;

and (2) mussels produce larvae that can disperse long distances before they settle on rocks and grow into adults.