ACD s and ASTCDs are white dogs (except for any patches). Pups are white at birth.
Colour intensity commonly (but not always) increases with age and varies from one part of the dog’s body to another. These colour changes are under the control of the ticking gene. The ticking gene, T, causes speckling or mottling of colour (black or red) to develop over the white by increasing the proportion of coloured (black or red) hairs versus white.
The varying proportions of coloured to white hairs is inferred to be under the control of modifier genes. We know little about these genes but, as with less complex traits, we may be able to select for or against them in our breeding programs. Robinson (Genetics for Dog Breeders) summarises:
“The white areas of many breeds, notably Pointer, Setters and Spaniels, are not clear, but covered with innumerable small pigment spots. This is known as ticking or flecking and is due to a dominant gene T. Ticking is not present at birth, but appears within a few weeks at the first moult. The expression is very variable, ranging from a few spots to such a profusion of spots that the white areas appear as roan. In long-haired breeds, the ticking simulates roan because of the greater intermingling of the hair fibres. … The expression of ticking varies from a lightly ticked dog with a few spots merely on the legs and stomach to the heavily spotted form found in a number of hound breeds … On the other hand, the ticking on some dogs, although profuse, tends towards flecking similar to but smaller and less distinct than that shown by the Dalmatian. Hence, there is not only wide variation of quantity of ticking but also of its quality. Evidently, ticking is a malleable character. Whether or not this indicates selection and stabilisation of the polygenes governing the expression of ticking has yet to be finally settled.”
Note. The roan gene does not operate in ACDs and ASTCDs.
Confusion has reigned as to the definition of “mottle” and “speckle”. Harry Spira (Canine Terminology) is clear and precise:
mottle: basically a bi-coloured pattern consisting of dark, roundish blotches superimposed upon a lightish background, giving an overall uniform appearance, e.g. the blue mottled variety of the Australian Cattle Dog”.
speckle: an alternative to the terms ‘flecking’ or ‘ticking’… very small areas of hair different in colour to an animal’s basic colour and distributed throughout the coat; usually dark spots on a white ground; e.g. Australian Cattle Dog.”
Spira’s definitions are consistent with the genetics of the inheritance and expression of the genes controlling this particular colour, described above. There is no need to distinguish ticked, from speckled or mottled (see also my Dalmatian Myth blog).
It follows that breeders can breed from, or towards, colour intensity, just as they can choose to breed blue ACDs or red ones. It’s just a little harder and needs more thought. Many years ago, when I first started breeding ACDs, an experienced ACD breeder, who knew nothing of formal genetics, gave me some advice. The principle is basically correct.
“If you are worried that your dogs are too dark, too like black-and-tan, you need to ‘break colour’. Introduce to your breeding program a very light-coloured, line-bred dog.”
The converse should apply to ACD lineages where near-white dogs are common. It is curious, though, that ACDs that are almost black-and-tan are now acceptable, even preferred by some, to the detriment of near-white ACDS.
Molecular genetics has advanced understanding of coat colour in dogs. Dog Coat Color Genetics updates and extends the chapter on genetics in A Dog Called Blue. In particular, the K locus was described after A Dog Called Blue was published and changes have been made to the nomenclature of the A series.