Helping dog breeders combat inherited diseases through understanding genetics.
Labrador Retrievers come in three distinct colours: black, yellow and chocolate. The colour of a dog depends on the presence of pigments in skin and hair. The pigments — which are made by specialised cells — occur as two distinct types. The first type is essentially yellow. The second one is dark, and varies from black to brown. The type of pigment that a Labrador produces depends on its genetic make-up and is the result of an interaction between two different genes, which we call the E and the B gene.
As we have already seen, a dog's genome contains two sets of genes, one from the father and one from the mother. So for each gene a dog can have two forms of that gene — if different forms of the gene exist.
Different forms of the E and the B genes exist. In genetics we commonly distinguish between two different forms of the same gene by using uppercase and lowercase letters. So the E gene has two forms, E and e. Similarly the B gene has B and b forms.