In plants and humans, the phenotype of an organism is determined by the genotype and the environment. (a) Plants from the genus Primula have different petal colours. The presence of the pigment malvidin results in blue petals. The metabolic pathway for malvidin synthesis is controlled by gene T/t. The presence of the dominant allele T results in blue petals. Another gene, gene D/d, at a different locus, also influences the malvidin synthesis pathway. When the dominant allele D is present, its gene product suppresses the malvidin synthesis pathway. This is summarised in Fig. 3.1. [Figure 3.1] A genetic cross was carried out between two plants heterozygous at both gene loci. The resulting offspring genotypes are shown in a Punnett square in Fig. 3.2. [Figure 3.2]