Final answer:
Directional selection is a process where one extreme of a phenotype is favored, leading to a shift in the population's characteristics and resulting in greater genetic variance. Stabilizing selection, on the other hand, narrows phenotypic variation by selecting against extreme variations.
Step-by-step explanation:
Directional selection is the process in which one version of a characteristic (or one end of a dimension) is represented in the next generation to either a greater or lesser degree. An example of this is the beak size of the Galápagos finches, where a shift was observed in the distribution toward larger beak sizes due to environmental shifts favoring such a phenotype.
The process described in the question is directional selection. Directional selection occurs when one of two extreme phenotypes is selected for, resulting in a shift in the phenotypic distribution towards that extreme.
An example of directional selection is the beak size of Galápagos finches observed by the Grants. When there is a change in the environment, such as a shift in food availability, finches with larger beaks may be favored and have a higher chance of survival and reproduction, leading to a higher representation of the larger beak phenotype in the next generation.
Directional selection results in greater genetic variance in a population compared to stabilizing selection, as it allows for the expression of new and different traits at one extreme of the phenotypic range., however, occurs when phenotypes at both extremes of the phenotypic distribution are selected against, resulting in a narrower range of variation. For instance, in a population of mice, those that best blend with the forest floor and avoid predation would most likely survive and reproduce, which leads to decreased genetic variance in the population.
Therefore, the answer to the question is c. Directional selection, as it results in a shift in the distribution toward one extreme, potentially leading to greater genetic variance within a population.