A brown and a black dog have a litter that includes puppies who are brown, yellow, black, and one they call parti. Two white dogs have an all-black litter. Rottweilers are known by their brown masks, and you wouldn’t recognize a Dalmatian without its spots. What’s going on? Is there a limit to the variety of colors and patterns in dogs? Can you breed a dog for a certain coloring?
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It’s all about genetics.
Dog cell nuclei contain 39 pairs of chromosomes. Each chromosome is made up of thousands of genes that determine everything from the dog’s sex to the color of their foot pads. An allele is a version of each gene, and one allele from each parent is passed on to the offspring. The dominant allele for each trait is the one that is responsible for the coloring and markings that we then see in the puppy.
The genetic makeup of the breeding dogs influences the range of colors and markings the puppies will display. The whole range of colors we see in dogs comes from two basic pigments found in dogs’ genes: eumelanin (black) and phaeomelanin (red). For example, the “dominant black” gene is responsible for a dog’s coat being black, regardless of the presence of other coat color genes. Similarly, the “recessive red” gene is responsible for a dog’s coat being red or yellow, regardless of the presence of other coat color genes. In addition to these coat patterns and colors, there are also a number of genetic factors that can affect a dog’s coat. All of the variations occur from the mix and balance of these two pigments, and different genes determine which will be expressed and how strongly.
This interplay of genes can result in a coat that is the deep red of an Irish setter or the gold of a yellow Lab. The pigments exist in the hair follicles, but they are not distributed evenly, so a dog might have dark hairs with light tips, known as agouti patterning. The uneven distribution of these genes also creates the various patterns, such as spotting, brindles, or masking seen in some dogs’ coats. When the genes do not trigger any release of pigment, it results in white spots or an all-white coat as seen in a West Highland white terrier or a Great Pyrenees. Eumelanin is also responsible for the color of a dog’s eyes, nose, and paw pads. If it is not produced in the eyes, the dog will have blue eyes (or even one blue eye!); if it isn’t produced in the nose, the dog will have a pink or liver- colored nose.
Basic coat colors
From those two pigments, there are four basic coat colors: black, brown, white, and red. Genetic variations cause dilutions that lead to a seemingly endless variety of colors and patterns. This is how we see dogs of every color from white to silver-grey to brown, red, or black. The genetic lottery also allows for color and marking variations within every litter.
Coat patterns
In addition to causing a variety of coat colors, genes influence the many coat patterns seen in dogs of different breeds.
The most common of these is the “agouti” pattern, which is characterized by banded hairs that are black at the base and lighter at the tip. This pattern is seen in many wild animals, and is also found in some breeds of domestic dogs such as the Border Collie, Australian Cattle Dog, and Basenji.
Another common coat pattern is the “sable” pattern, which shows as a reddish-brown base color with black tips. This pattern is seen in breeds such as the German Shepherd, the Welsh Corgi, and the Shetland Sheepdog.
The “merle” pattern is characterized by a mottled or marbled appearance of the dog’s color over lighter fur. This pattern is caused by a gene mutation and is seen in breeds such as the Australian Shepherd, the Cardigan Welsh Corgi, and the Great Dane.
The “brindle” pattern is characterized by a base coat color with darker stripes or patches, often giving a ‘tiger-stripe’ appearance. This pattern is seen in breeds such as the Boxer, the French Bulldog, and the Staffordshire Bull Terrier.
Finally, the “parti-color” pattern is characterized by a dog having two or more distinct colors in their coat. This pattern is seen in breeds such as the Australian Cattle Dog, the Bichon Frise, and the Pomeranian.
The “albino” gene is responsible for a complete lack of pigmentation in a dog’s coat, and is seen in breeds such as the English Bulldog, the French Bulldog, and the Boston Terrier.
There are certain breeds that display unique coat patterns. Great Danes are the only dogs to have a “harlequin” pattern of irregular black patches on a white background. The harlequin gene does not produce pigment, but it limits the expression of another gene.
Rottweilers, Doberman pinschers, and Boxers carry two copies of the recessive gene for “tan points” and “masking”, which give them their distinctive markings. Their main color is solid black, brown, or ‘blue’, and they have tan marks above their eyes, on their muzzle, two patches on their chest, on their lower legs and feet, and under their tail.
Health concerns and breeding considerations
Unfortunately, in some dogs the genetic makeup that is responsible for certain patterning can also predispose the breed to serious health problems. Breeders who strive for a specific genetic mix need to be careful not to mate two dogs who could lend harmful genes to their offspring.
Primarily white harlequin Great Danes, for example, are much more likely to experience deafness and vision problems than Great Danes with other color coats.
Breeding for a merle pattern should be done with careful genetic consideration, as dogs who inherit a double merle gene, one inherited from each parent, are at increased risk of problems with their ears and eyes, causing deafness and/ or blindness. Since the gene for merle is recessive, a breeder might not know by coat color whether a dog carries it, and genetic testing is the only safe way to know for sure. The American Kennel Club will not register puppies from two merle parents.
With the right genetic information, it is possible to have a clear understanding of the colors that could result from a breeding pair. It is important to remember, however, that each puppy will have the same odds of expressing a certain coloring gene, which can lead to a multi-colored litter—and maybe that surprise group of black puppies from two white parents.
Sources:
https://www.akc.org/expert-advice/dog-breeding/merle-in-dogs/
https://www.ucdavis.edu/curiosity/news/dog-coat-patterns-have-ancient-origin
