Collie colours and genetics
Rough and smooth collie standard recognizes three colours:
Sable stands for any shade of light gold to rich mahogany or dark shaded red.
Tricolour is predominantly black with tan markings on legs and head.
Blue Merle is clear, silvery blue, splashed and marbled with black. Tan markings are preferred, but their absence should not be penalised. It is the only colour where blue eyes are allowed.
All of the above may carry typical white collie markings to a greater or lesser degree. Following markings are favourable: white collar, full or part; white front, legs and feet; white tail tip. A blaze may be carried on muzzle or skull, or both. All white or predominantly white is most undesirable in Europe, but it is recognized and bred in the United States.
Two types of pigment
Every dog's coat colour is composed out of the two types of pigment: eumelanin (black) and phaeomelanin (red/yellow). In many dog breeds only one of them is present - for example black labradors only have eumelanin, and the yellow ones only phaeomelanin. However, some dog breeds can have both at once. If this is the case, pigments will not spread equally through the coat like in human hair, but will alternate through every single hair differently, as pictured below. A pattern like this is called Agouti, and is responsible for a wide range of different colours and shades - from light golden to wolf gray or black & tan. Every time you see both black and red markings on a dog, it is always some form of agouti. This also includes all collie colours.
The arrangement and amount of pigments in the agouti hair can vary from completely yellow, or yellow with a black tip, to predominantly black, possibly with a small yellow ring in the middle (pictured left). The pattern is defined by genes, dog's age, coat length, and the position of the hair growth. Thus, for example, sable collies always have black tips concentrated around their ears, on their back and tail, while the rest of their body is mostly golden. Tricolour is also a form of agouti, where the black pigment is dominant, leaving only a few golden areas on cheeks and legs.
If you take a close look at a single black hair of a tricolour collie, you may see it contains a small amount of phaeomelanin, and many of them do, as it is shown in the picture above. These yellow rings are usually very discrete, not affecting the quality of black colour. However, in some dogs they can be more noticeable, giving the black colour an undesired grayish shade. Another possible fault in black colour is a rusty tinge, which many people incorrectly associate with too much of red pigment, while, in fact, it has nothing to do with phaeomelanin. The cause is a poor quality of eumelanin (black pigment). It is important to notice that none of these faults, neither grayish nor rusty, are related to mating with sables. On the contrary, breeding to a sable with good quality black pigment (which is not always easy to recognize) can actually improve bad black colour. The quality of eumelanin is especially important in the case of breeding blue-merles, who, without a perfectly deep black background, can never display the desired blue shade.
It is also interesting to note that agouti colours change with age. Sable collies are born very dark. At few months of age, their colour clears to light golden and then, as years go by, eumelanin starts taking over again, gradually darkening the colour, year by year. This is the reason why it is sometimes possible for the grayish/yellowish shade in a one year old black (or blue) dog to improve with age. Dark sable shades are generally more noticeable on longer coats, that is why mahogany colour is mostly seen in roughs. Smooths are, in the best case, very heavily shaded.
At least three sets of genes are involved in determining the collie colour. The first one controls the arrangement of pheaomelanin and eumelanin - in other words, it defines sable or tricolour colour of a dog. The second set is the merle factor. The third one controls the amount and the position of white markings.
1. sable or tricolour?
Agouti (A) locus is the set of genes controlling arrangement of eumelanin and phaeomelanin in dog's coat. This series contains few different alleles, responsible for many different shades and patterns. The general rule is that yellow patterns (those with more phaeomelanin) are dominant. Two of these patterns are present in collies: sable and tricolour. Sable is inherited as a dominant trait.
Merle (M) indicates incomplete, dominant gene, responsible for the random dilution of eumelanin, turning it into clear, silvery blue splashed with black. It has almost no effect on phaeomelanin. Merle, itself, is not a colour, but a pattern. Applied to different backgrounds it produces different colours - a blue-merle dog is in fact a tricolour dog with the merle pattern. The merle pattern on sable background produces the sable-merle colour, which is not recognized by the FCI standard.
Sable-merle puppies are born out of sable and blue-merle matings, at 25% rate. Many factors influence the way sable-merle colour looks like, but it is mostly related to the amount of eumelanin in the agouti pattern. If a dog is heavily shaded, the sable-merle colour will appear like randomly diluted areas of dark colour, mostly on the head, back and tail - the areas containing most eumelanin. Sometimes, in light golden dogs, it is not even possible to detect the presence of merle, unless we have seen them as a few days old puppies, when they are still dark enough for merle to be noticeable. Also, a sable dog with blue or blue-flecked eye is most likely to be a sable-merle.
The danger related to the merle gene is its ability to completely destroy most of the pigment when in homozygous form (MM). This sometimes includes the pigment in the inner ear and the back of the eye, necessary for normal hearing and eyesight. Such a puppy can only be born from both merle parents, at 25% rate. It is usually predominantly white, and often deaf and/or blind. If it survives and, at some point, mates with a tricolour, it will produce a normal, healthy litter of all blue-merles. Deafness and blindness, in this case, are a direct consequence of lacking pigment, and cannot be inherited separately from white colour.
The blue-merle colour represents a great challenge for breeders. Due to the limited range of mating partners (generally, only tricolours are considered) and many details that have to be taken into account, it is not easy to breed a truly great, perfectly coloured representative of the breed.
3. white markings
Spotting (S) locus controls the amount and the placement of white markings ona a dog.
What exactly are white markings?
The simplest definition would be - the areas without pigment. Every hair that contains neither phaeomelanin nor eumelanin will appear white to the human eye.
The pigmentation development in a dog embryo starts during first 40 days of gestation. At first, melanocytes appear along the spinal column and brain, later migrating towards the extremities - paws, muzzle and the tip of tail. The process is regulated by spotting series of genes. These genes determine if the melanocytes will reach their destination, or stop at some point, leaving some or most parts of the dog white. Generally, the patterns with less white are inherited as a dominant trait.
According to the FCI standard, collies carry white markings around their neck, chest, legs and feet, the tip of the tail and the blaze on the head, shown in pictures 5 - 7. The allele responsible for that kind of pattern is called Irish Spotting. All collies carry that same genetic code.
Why mention this set of genes if there are no differences within the breed?For two reasons. The first is American Kennel Club standard, that allows white collies. These whites have nothing to do with the ones from merle x merle breeding. Their colour is controlled by the recessive gene from the S-series, and coloured head on predominantly white body is usually the result (picture 1-2). The white gene is recessive, and carriers usually look like standard coloured specimens, only with more pronounced white markings, and/or sometimes some white inside the coloured area (picture 4-5). It is highly unlikely that any of these dogs will ever have problems with seeing or hearing. As described earlier, the pigment development always starts in the spinal column and brain, slowly migrating towards extremities. No matter how early it is interrupted, the inner ear will most likely end up pigmented, unlike in double merles, whose pigment is destroyed randomly, with a much greater chance of the inner ear being left white.
The second reason is to illustrate how unpredictable white markings are. Besides the spotting gene, many factors can influence the pigmentation pathway. Even external conditions - for example it is possible that stress or sickness in mother's pregnancy affect melanocyte migration, causing slightly more white markings on puppies than usual. Also, there are many modifier genes that take part in determining white markings. We are not even able to decypher most of them. One of the known modifiers for spotting is the merle gene. Although not directly related, it seems to cause more white in merle puppies than in non-merle siblings. White markings on the head are probably controlled by separate genes, but it is not yet determined which, or how it works. That is why it impossible to predict the amount and the placement of puppies' white markings.
Another interesting feature related to the melanocyte migration is that it does not stop at birth. It continues through the whole life, only much slower. The best examples are wide, white blazes on foreheads of newborn puppies that later decrease, or even disappear. The parts towards the nose (or extremities in general) will never decrease as much as those on the forehead or back.
Try different mating combinations
Did you know...?
- Although least famous, the blue-merle colour is one of the oldest and most typical collie colours.
- The first sable collie appeared as late as 1868. His name was Old Cockie and his lineage remained a secret forever.
- In the original book, Lassie was described as a tricolour female. Since there was no properly trained tricolour in the time of filming, the role was given to a sable male named Pal.
- It took much longer for sables to spread in smooths than in roughs. In the eighties, it was almost impossible to find a sable smooth champion in the UK. Today there are many, but still not as many as in roughs.