BIO 182 Exam 2 Questions With Complete Solutions

How many modes of selection are there? correct answer: 3 What are the modes of selection? correct answer: Stabilizing selection, directional selection, and disruptive selection Stabilizing Selection correct answer: The mean of the trait remains similar over time but the standard deviation decreases Directional Selection correct answer: The mean phenotype shifts in a particular direction Disruptive Selection correct answer: The standard deviation of the trait increases as individuals with the mean value disappear. Stabilizing Selection Explained correct answer: The stronger the selective pressure against extreme phenotypes, the narrower the distribution of phenotypes will be in future generations. In the end, the size of the standard deviation will reflect both the strength of selection against extremes and the frequency of mutations creating new variation. Thus, when we observe a wide range of phenotypes in a population, we might infer weak selective pressure against the extremes. Directional Selection Explained correct answer: The population's environment changes. The mean phenotype in the population may no longer be the phenotype that reproduces the most. Over time, we should expect the mean phenotype to shift higher or lower, depending on the direction of selective pressure. Once the mean phenotype catches up to the change in the environment, stabilizing selection will resume. The environment must change slowly enough for the population to persist. If the environment changes too quickly, no members of the population will be able to reproduce, leading to extinction. Disruptive Selection Explained correct answer: A population can occupy an environment in which individuals with extreme phenotypes reproduce more than individuals with the mean phenotype. This mode of selection occurs when several distinct strategies confer greater reproductive success than other strategies do. Can produce new species when individuals choose to mate