The directional selection is a type of Darwinian selection where a particular phenotype is favored in the population, thereby modifying the allelic frequencies to increase the proportion of the favored phenotype. <em>Biston betularia</em>, also known as peppered moth, is a species that was influenced by directional selection in its recent past. Before the industrial revolution, the frequency of light-colored moths was predominant compared to the darker-colored phenotypes, because this color has higher adaptive fitness in a clean, no pollution environment, thereby light-colored moths were able to avoid predatory birds. However, during the industrial revolution, the frequency of dark-colored moths increased in response to pollution (i.e. darker environment), thereby conferring a higher adaptive fitness to darker phenotypes.
the growth of the parts of plants with respect to the force of gravity. The upward growth of plant shoots is an instance of negative geotropism; the downward growth of roots is positive geotropism.
