(a) Cats with either black fur or white fur are common in Europe, whereas cats with brown fur are less common. A gene, coding for an enzyme involved in pigment production, has two alleles. • The dominant allele, B, results in black fur. • The recessive allele, b, results in brown fur. A second gene can affect fur colour. • The dominant allele, A, prevents pigment production, resulting in a cat with white fur. • The recessive allele, a, has no effect on fur colour. The two genes are on different pairs of autosomes. Use a genetic diagram to show how a cross between two cats, heterozygous at both loci, can produce offspring with three different colours: white, black and brown. State the expected ratio of the different coloured offspring.

1. (a)Use a genetic diagram to show how a cross between two cats, heterozygous at both loci, can produce offspring with three different colours: white, black and brown. State the expected ratio of the different coloured offspring.[6]
2. (b)Suggest how the presence of allele A prevents pigment production.[3]