Final answer:
Directional selection is the type of selection in which one allele confers greater fitness over another allele. It leads to a shift in phenotype distribution towards the favored allele and a decrease in genetic variance in the population.
Step-by-step explanation:
Directional selection is the type of selection in which one allele confers greater fitness over another allele. This results in a shift in phenotype distribution towards the favored allele. An example of directional selection is the increase in the number of dark-colored moths after the Industrial Revolution, as they were better camouflaged than light-colored moths. Directional selection leads to a decrease in genetic variance in a population as the favored allele becomes more prevalent.