The flowers of the primrose (Primula vulgaris), are polymorphic. The two most common forms occur on separate plants and are termed as 'pin-eyed' (long style and lowered anthers) and 'thrum-eyed' (short style and highly placed anthers).

In most localities, pin-eyed and thrum-eyed plants are found in equal proportions. The flowers are pollinated by insects, such as bees, which have a long proboscis or tongue. The bee pushes its head into the mouth of the corolla tube and the proboscis is extended to collect the nectar at the base of the flower.
Explain how the polymorphism is likely to increase the variability of the offspring of primrose plants.

Explanation

Polymorphism in the flowers of Primula vulgaris ensures cross pollination and does not permit self pollination. Cross pollination introduces variability in the offspring.