The foxglove, Digitalis purpurea, is a common plant in many parts of the world. Fig. 5.1 shows a foxglove. [Figure 5.1] Flower colour in foxgloves is controlled by two genes that interact with each other. • Dominant allele M codes for an enzyme involved in the production of a purple pigment. • Recessive allele m codes for a non-functioning enzyme so no purple pigment is produced, resulting in a white colour. • Dominant allele D interacts with allele M to produce dark purple flowers. • Recessive allele d does not interact with allele M. • Neither allele D nor allele d interact with allele m. A double homozygous foxglove with dark purple flowers was crossed with a double homozygous recessive foxglove with white flowers. All the offspring had dark purple flowers.

1. (a)Explain what is meant by the term homozygous.[1]
2. (b)Using the symbols above, state the genotype of the offspring with dark purple flowers.[1]
3. (c)Two of these offspring with dark purple flowers were crossed. This cross produced a mixture of plants with three different flower colours: • dark purple • purple • white. Draw a Punnett square to show the possible genotypes and phenotypes of the mixture of plants from this cross. Write down the expected ratio of plants with each flower colour. ratio[6]

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