A woman buys a packet of seeds for red flowering plants. In the spring, she plants the seeds in her garden and enjoys beautiful red flowers all summer. The flowers are self-pollinating, and many of the flowers produce seeds. The woman collects these seeds and plants them in her garden the following spring. She is surprised when about one-fourth of these plants produce white flowers while the other three-fourths produce red flowers. Assuming that the seeds were all produced by self-pollination of the parental generation, which statement best explains the reason for the woman’s observations?