Arabidopsis thaliana is a plant that serves as a model organism in plant biology and genetics studies. Like many plants, A. thaliana has hair-like outgrowths on its leaves and stems, called trichomes, that prevent herbivory by secreting inflammatory chemicals. Like any phenotype, trichome number is inherited and vulnerable to selective pressures from the environment.
A pair of biology students grew 175 A. thaliana wild-type plants, starting from seeds. They observed several variations in the number of trichomes on each plant, and plotted their data in Figure 1 below:
They set out to examine how the phenotype distribution could change in a second generation if the trait for trichome number was selected for. They used a cotton swab to brush pollen from the top 10% of hairiest plants (greatest number of trichomes) and cross-pollinated the flowers in this selected population. At the end of their six-week life cycle, all the fertilized A. thaliana plants developed seeds, which the students planted, keeping the seeds from the selected population separate from the control population. When all the new seedlings were about two-weeks old, the students counted the number of trichomes on each plant and graphed their data in Figure 2 below:
Which of the following is a plausible explanation for their results?