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Chapter 23: Q23.1-1CC (page 487)
Explain why genetic variation within a population is a prerequisite for evolution?
Genetic variation acts as an evolutionary force and alters the arrangement of alleles in the present population. The inheritable variation undergoes natural selection and causes evolution in the population.
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If a population stopped reproducing sexually (but still reproduced asexually), how would its genetic variation be affected over time? Explain.
This kettle lake formed 14,000 years ago when a glacier that covered the surrounding area melted. Initially devoid of animal life, over time, the lake was colonized by invertebrates and other animals. Hypothesize how mutation, natural selection, genetic drift, and gene flow may have affected populations that colonized the lake.
Researchers studied genetic variation in the marine mussel Mytilus edulis around Long Island, New York. They measured the frequency of a particular allele (lap 94) for an enzyme involved in regulating the mussel鈥檚 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 lap 94 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鈥�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鈥�11 compared 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.
Suppose two plant populations exchange pollen and seeds. In one population, individuals of genotype AA are most common (9,000 AA, 900 Aa, 100 aa), while the opposite is true in the other population (100 AA, 900 Aa, 9,000 aa). If neither allele has a selective advantage, what will happen over time to the allele and genotype frequencies of these populations?
Natural selection changes allele frequencies because some _________ survive and reproduce better than others.
(A) alleles
(B) loci
(C) species
(D) individuals
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