The genes that each of living organism have control who they are by affecting proteins in their bodies. Different genes give rise to the differences you see within a population, everything from hair/coat colour to disease susceptibility. Whilst an understanding of coat colour genetics is useful when breeding please remember that it should be one of the last considerations when breeding a litter – health, temperament and type are far more important.
The are many different genes in the dog that affect coat colour and texture/length. A single gene does not always give raise to a single trait, but it’s the interaction of multiple genes that give raise the massive variety we see.
All hair follicles are made up of 2 pigments – Eumelanin and Phaeomelanin – which give the hair strand it’s colour. Both pigments are a form of melanin and have a default colour which is altered by the genes. Genes give rise not just the colour of the cost but also the distribution of these pigments, telling certain cells to produce Eumelanin, Phaeomelanin, or neither. As the hair grows from the follicle cell it will take the colour of the pigment being produced at that moment in time. If the cell switches at any point, the hair colour will change, giving raise to banded hair strands, and dogs changing colour as they get older (eg getting darker).
Eumelanin is, by default, a black pigment, found not only in hair follicles but also other areas of the dog that have colour, such as the nose & eyes. Any black area on a dog is caused by the cells producing eumelanin. However, there are genes that restrict and/or alter the production of eumelanin, resulting in cells which are unable to produce the normal amount of pigment, or none at all. These genes will result in the whole of the dog’s coat being changed colour (and the nose/eye rims). Dogs with reduced eumelanin can be liver/chocolate (brown), blue (grey) or lilac/isabella (dusty brown), the later, both being referred to as dilutes. Dogs that are unable to produce any Eumelanin but their “pigmented colour” can discerned from their nose (genetically black dogs have a black nose; genetically liver dogs have a brown nose).
Phaeomelanin is the other pigment and is found only in the coat, and is a red pigment, giving raise to the array of red dogs out there – from the cream of the palest Labrador through to the bright red of an Irish Setter. Phaeomelanin is only produced in the coat so the nose/eyes will still the colour of the eumelanin, thus showing the “pigmented colour” of the dog. Red dogs don’t appear in a variety of colours, just one colour which varies in intensity, based on other genes that are present.
White is not generated by another pigment in the coat, but by the absence of both of the above pigments, resulting in hair that is totally natural and “un-dyed”. Sometimes the whole dog is affected, resulting in a white coat, whereas at other times just parts are affected, giving raise to specific areas of white in amongst the rest of the colour.