For each of the seven pairs of characters examined, it was observed that one allelomorph dominated over the other, so that F1
exhibits one or the other alternative phenotypes represented in the parents.
However, soon after rediscovery of Mendel's laws, experiments were available to show that in some cases the F1
individual showed the phenotype which was intermediate between the two parents. For instance in four-o'clock plant (Mirabilis jalapa)
it was found that when plants with red flowers were crossed with those having white flowers, plants with pink flowers were obtained in F1
generation. This would then give rise to red, pink and white flowered plants in 1 : 2 : 1 ratio in the F2
generation. Similarly in snapdragon, plants With broad leaves and plants with narrow leaves give rise to plants with intermediate leaves in F1
generation. Likewise, plants with red flowers and plants with white flowers give rise to those with pink flowers. If a dihybrid cross is made using broad leaves and red flowers in one parent (BBRR)
and narrow leaves and white flowers in the other parent (bbrr),
will have intermediate leaves and pink flowers. In the F2
generation nine phenotypes corresponding
to nine genotypes will be observed. A summary showing nine different genotypes and phenotypes is given in Table 2.9.