DNA, Jellybeans & Coat Color
I have gotten quite a few questions regarding canine color genetics from those interested in the topic I will do my best to explain what I know. Please understand, I am NOT a Canine Geneticist, nor do I hold any advanced degrees in canine genome. I am taking on-line courses through The Institute of Canine Biology and I am an avid reader and Super Geek. In other words, I find the topic very interesting and know just enough information to get me into trouble…but here goes nothing!
A simplistic way to explain canine color coat is through jellybeans. Buy two bags of jellybeans and label one bag: DAM and the other SIRE. Now, set out 6 bowls and without thought to any color combination, pour a dozen from each bag into each bowl. Each bowl represents a possible puppy and its possible genetic components. This crude experiment will give you some idea of the possible random combinations that produce certain color traits.
QUESTION: So, if the jellybeans or puppy markings produced are random, how does a breeder know what the puppies coloring will be? ANSWER: The breeder is playing the odds and know how the color genetics react/ respond to other genetics that are in the mix. Let’s take a chocolate yorkie puppy. To achieve that, BOTH the Sire and the Dam MUST carry at least one (b) chocolate gene. (This theory is true for all recessive genes.) Meaning, for it to be expressed (visible to the eye) in the puppy, BOTH parents must carry it. So, to have a litter of chocolate puppies, you need chocolate parents-that makes sense. But, what if you have a Chocolate-Parti DAM and a Chocolate SIRE, that carries blonde? What color could the puppies be? Well, that depends on what color genes both parents carry:
CHOC-PARTI DAM: We know that she is the (bb) gene because of her chocolate color. We also know she is the (ss) gene because of the white/ piebald markings, but we are not 100% sure about the other genes she may carry. So the remaining color genes are a crap shoot.
CHOC SIRE: He is the bb gene that give him his chocolate color and liver nose and paw pads, but he is also a carrier for the (E/e) gene, blonde meaning he can pass along this gene to his offspring.
LITTER OUTCOME: Chocolate, Traditional & maybe Chocolate/Blonde Puppies, if the DAM carries blonde
This all goes back to 7th grade science class. (Now, I bet you wished you had paid attention a little more; I know it did…) Fabulous Punnet Squares. If you are interested in learning more about each color gene specifically, please check out the information below:
Eumelanin is basically black pigment and cells producing it are responsible for a black dog coat color. However, there are genes which cause changes in eumelanin to produce liver (brown), blue (gray) or isabella (dusty pale brown) coat color. Genes responsible for this change cause altering of production of the eumelanin in cells, so the cells cannot produce full-strength pigment.
For this reason, isabella and blue dogs are known as ”dilutes”. Eumelanin can be found also in nose and eyes (irises). Depending on dog’s genes, nose can be also black, liver, isabella or blue. The other pigment is phaeomelanin, which is red. It appears as a deep red (like Irish Setters), light cream, encompassing gold, yellow and orange. Most dogs have both eumelanin and phaeomelanin, and the way those two pigments mix is controlled by A (agouti) locus.
The white coat color in dogs is not caused by any pigment, but cells that are not able to produce any pigment. The whole animal can be affected, in similar way to albinos, or it can be localized, like the white markings of coat.
Dog Coat Color Genetics
Today’s scientists and breeders are familiar with locations on chromosomes, or loci, responsible for appropriate dog coat color, which in turn depends on the dog’s descent. Each dog has two alleles for each locus. Two alleles in one locus can be the same, and in that case the dog is homozygous for that specific gene. Conversely alleles can differ and in these cases the dog is heterozygous; from the two alleles the dominant one will be expressed. Differing loci affect related pigments differently.
A locus (Symba’s coloring)
A locus is also known as the Agouti locus. It affects distribution of both, eumelanin and phaeomelanin. The agouti series contains four alleles: ay (sable), aw (agouti/wolf grey), at (tan points), and a (recessive black). Hierarchically they are ordered: Ay > aw > at >a. It is important to know that the genes of A series can be expressed only when there is no dominant black allele K on the K locus. In the case of one dominant black allele, a dog can be genetically a sable, tan points or agouti but that will never be expressed.
Sable is the top dominant gene in the agouti series. This means that one allele of sable (ay ) is sufficient for the gene to be expressed. It is expressed in three common patterns: clear sable, tipped sable and shaded sable. Sable dogs have red colored coats with eumelanin (black/blue/isabella/liver).
Agouti or Wolf Grey is one of the most common coat color in mammals. It can be found in many wild animals such as rabbits, deer, rodents and wolves and the reason it is so common is because of the camouflage it provides. The Agouti’s dog coat color is specific for fur branded in different colors. This means that the cell is producing different pigments during different stages of hair growth. The gene responsible for changing the pigment is aw, where ”w” stands for ”wild type”. Gene aw dogs inherited their genes from wolves, and can be seen expressed in many dog breeds closely related to wolves. Often it is difficult to distinguish agouti from shaded sable, but the main difference is the banded hairs. Another specific is that an agouti dog coat color can lighten significantly as it ages.
The almost bottom gene in the agouti series is the tan points (at) gene, which means that in order for it to be expressed, the dog must be homozygous, containing two at alleles, or heteroyzgous with ata genotype. The only gene under the tan points gene is the recessive black, which is very rare. Red or tan appears above the eyes, on the dog’s muzzle, cheeks, the front of neck and the lower legs and feet; the intensity of color deepens on the gene. The main color is black, or any other eumelanin color (isabella, liver or blue).
Saddle pattern and creeping tan are modifiers of the tan point gene. Creeping tan causes that black (or other eumelanin color) on black-and-tan retreats on a dog’s back, spreading the red area around the eyes and legs, compared to black-and-tan dogs. In the saddle pattern, red extends over an even bigger part of body, leaving black only on the dog’s back, tail and back of the neck.
B locus generates a brown dog coat color, also called liver. It affects only eumelanin, causing all black colors in the coat turn to a brownish color. It is expressed by a recessive gene, so the dog must be homozygous (genotype bb) in order to be brown. A brown puppy can have black parents, which in this case will be heterozygous (genotype Bb), where the puppy has inherited one copy of gene b from each parent. It is genetically impossible for a liver-colored dog to have any black hairs in their coat, or for a black or blue dog to have any liver in its coat. Depending on alleles in the A and K locus, brown dogs can have some red (phaeomelanin) hairs expressed. It also affects the color of the nose and eyes, making the eyes light brown or amber and the nose brown. Brown can be the whole coat, in just some parts of the coat or in specific patterns such as solid liver, liver with white markings, piebalds with roaning, liver with traditional tan markings, grizzle/agouti liver, liver merles, liver sable, liver with greying genes and red coat color dogs with a liver pigment.
D locus contains a dilution gene, which is recessive, so the d gene is dilution and the D gene is non-dilution. This means that in order for the dog to be dilute it must be homozygous (dd genotype), and if it is heterozygous (Dd genotype) it will have normal, not diluted pigmentation. The dilution gene affects both eumelanin and phaeomelanin. When homozygous with a dilution gene, a black dog becomes blue and a liver dog becomes isabella. The gene affects also nose and eye colors. In blue dogs the nose will be blue pigmented and isabella dogs are slightly darker than liver. Eyes will lighten to amber.
E locus (Jodi’s coloring)
E locus is responsible for almost all non-agouti eumelanin or phaeomelanin patterning in dogs. E stands for ”extension”. Alleles in E series are Em (masked) , Eg and Eh (grizzle/domino) , E (normal extension-has no effect on phenotype) and e (recessive red).
Em allele causes an eumelanistic mask, which can be black, liver, blue or isabella on the muzzle and sometimes the ears. The mask is expressed only in genetically sable, tan-pointed, saddled or agouti (wolf grey) dogs, which means that the mask’s expression depends on genes on the A and K locus, while in dominant black dogs it will not be present. Since the mask consists of eumelanin pigment, genes controlling the coat color intensity can also affect the intensity of the mask.
In some breeds, the mask can cover a large part of body, covering chest and legs, while in others extreme masking can ”hide” tan points.
As stated previously, from two alleles of the E locus, allele E stands for normal extension, which has no effect on phenotype, and e stands for recessive red. A homozygous dog with an ee genotype will not have the ability to produce any eumelanin, and so will be completely red. Recessive red dog coat color is recessive in its own series, but dominant over other loci. Dominant black, sable, tan points, wolf grey, merle, and any other pattern with black in it will be turned to solid red by the recessive red gene. This is the main danger of the recessive red dog coat color gene, it masks a lot. It appears only in some breeds, but it is difficult to distinguish an unmasked sable from a recessive red dog.
Recently discovered on E locus are alleles are Eg and Eh. The Eg gene is specific to the Saluki, the Afghan hound and the Borzoi; it has not yet been identified in any other breeds. The Eg gene is dominant over E locus, which means a dog carrying this gene cannot have a mask. The Eh allele has recently been discovered in English Cocker Spaniels, and is very similar to the Eg gene, affecting dominant black dogs.
There are three K locus genes: K (dominant black), kbr (brindle) and k (non-solid black – allows A locus to be expressed). The K gene is the top dominant; the k gene is bottom dominant. The genes are expressed in the following order: K> kbr>ky.
Homozygous (kbrkbr genotype) or heterozygous (kbrky genotype) dogs will have any allele on A locus expressed, but all phaeomelanin will be brindled. Brindle usually appears as black stripes (eumelanin) on a red base (phaeomelanin). The intensity of the brindling will depend on the gene on A locus; a dog with brindle gene can be solid brindle, black with brindle points or solid black, liver, blue or isabella.
Sometimes a brindle dog coat color with black pigment can appear with silver-like stripes on a creamy background.
Coat Color DNA Testing
To be able to predict the dog coat color of future cubs, it is vital to know the family tree but even then it is not always possible to be certain. Genes for some dog coat color or patterns are recessive and can be hidden throughout generations, but they are genetically present and can be expressed when the dog is bred with a dog of a specific genotype. Genetic testing is the only way to be certain of dog coat color genetic heritage.