The Labrador is a variety of domestic dog. Labradors have fur that can be brown, black or yellow. In Labradors, TYRP1 is one gene that codes for fur colour. This gene has two alleles, B and b. • The dominant allele, B, codes for the enzyme tyrosinase that functions in the pathway to produce melanin, leading to black fur. • The production of melanin in Labradors is very similar to the production of melanin in humans. • The recessive allele, b, codes for an enzyme that results in the production of a brown form of melanin, leading to brown fur.

1. (a)Outline how melanin may be produced in Labradors to produce black fur.[2]
2. (b)(i)Construct a genetic diagram to show the ratio of possible offspring from a cross between a black male Labrador, heterozygous for both genes, and a yellow female Labrador, heterozygous for TYRP1. parental phenotype parental genotype gametes offspring genotypes offspring phenotypes ratio[6]
3. (b)(ii)State the term used to describe a protein that is involved in the control of gene expression in eukaryotes.[1]