R. C. Punnett conducted experiments on the inheritance of traits in the sweet pea, Lathyrus odoratus. In one experiment, he crossed two different true-breeding sweet pea plant strains, one with erect petals and long pollen, and the other with hooded petals and round pollen. All the offspring (F1F1 generation) had erect petals and long pollen (Figure 1).
Next, Punnett allowed the F1F1 generation to self-fertilize and recorded the phenotypes of their offspring. The data are shown in Table 1.
Which of the following best explains how the sweet pea plants in the parental generation produce F1F1 offspring with 14 chromosomes?