4 Domestic goats, Capra hircus, show a wide range of coat patterns and colours. One gene involved in coat colour and pattern has multiple alleles. Four of these alleles are: • A, the allele for white, is dominant to all others • Ab, the allele for badgerface (stripes on face) and Aº, the allele for grey, are codominant • a, the allele for black, is recessive to all others.

1. (a)State all the possible genotypes of: a grey badgerface goat a white goat.[2]
2. (b)A cross between a black goat and a white goat produced a white goat. This white offspring was crossed with a grey goat. The genotype of the grey goat was not known. Use genetic diagrams to show all the possible offspring genotypes and phenotypes that could result from the cross between the white offspring and the grey goat.[4]
3. (c)When goat skin cells produce black melanin pigment these events occur: • Melanocyte stimulating hormone (MSH) is secreted into the bloodstream. • MSH binds to the melanocortin 1 receptor on the cell surface membranes of skin cells. : This causes a rise in cyclic AMP within the cell. The enzyme tyrosinase is activated and begins melanin production. The white allele A codes for a protein that binds irreversibly to the melanocortin 1 receptor. No rise in cyclic AMP occurs, even when MSH is present in the blood. Explain the appearance of goats with genotype aa.[2]