Inheritance of petal colour and pollen shape in sweet pea plants are controlled by two genes. • Gene P/p controls petal colour. Allele P for purple petals is dominant to allele p for red petals. • Gene G/g controls the shape of pollen grains. Allele G for long pollen grains is dominant to allele g for round pollen grains. [Figure 2.1] shows the structures inside a flower from a sweet pea plant. [Figure 2.1] Sweet pea plants are normally self-fertilising. Pollen grains containing the male gametes are produced in the anthers and released into the flower. The pollen grains fall on the stigma in the flower, leading to fertilisation of the female gametes. A plant breeder cross-fertilised two sweet pea plants, A and B. A homozygous dominant plant with purple petals and long pollen grains (plant A) was crossed with a homozygous recessive plant with red petals and round pollen grains (plant B). The breeder transferred pollen grains from the flowers on plant A to the flowers on plant B.