In sweet pea plants, an allele for purple flowers (P) is dominant when paired with a recessive allele for red flowers (p). An allele for long pollen grains (L) is dominant when paired with a recessive allele for round pollen grains (l). Bateson and Punnett crossed a plant having purple flowers and long pollen grains with one having white flowers and round pollen grains. All F1 offspring have purple flowers and long pollen grains. Among the F2 generation, the researchers observed the following phenotypes:

296 purple flowers/long pollen grains

19 purple flowers/round pollen grains

27 red flowers/long pollen grains

85 red flowers/round pollen grains

What is the best explanation for these results?