The patty pan squash plant, Cucurbita pepo, produces edible fruits that vary in colour. (a) The colour of the fruits is controlled by two genes, A/a and B/b, that occur on different chromosomes. • Allele A produces a white fruit colour. • Allele a does not produce a colour by itself but allows the colours coded by gene B/b to show in the phenotype. • Allele B produces a yellow fruit colour. • Allele b produces a green fruit colour. In a dihybrid cross, an AABB plant was crossed with an aabb plant. All the resulting F1 plants produced white fruits. The F1 plants were then crossed with each other to obtain the F2 generation.