Coat Colour Genetics
Have you ever wondered how your dog came to be the colour he is? This article will hopefully explain a little bit about how colours are inherited and why there is such a wide range of colours in the Chinese Crested.
Chinese Cresteds are colorful, and these colors comes from a wide range of genes. The genes combine to determine the coat color and the coat pattern.
It is important to remember that mammals have only two forms of melanin in their coats. One, eumelanin, is dark, though it can vary somewhat in color due to variations in the protein that forms the framework of the pigment granule. The base form of eumelanin is black. Eumelanin can also appear brown (often called liver or chocolate) or blue-gray due to genes affecting the color.
The second pigment called phaeomelanin, is red. Phaeomelanin and can vary in color from pale cream through shades of yellow, tan and red to mahogany.
There are at least several gene series that determine where, on the dog and along the length of the hair, eumelanin and phaeomelanin appear.
B-locus (black-brown)
B-locus is a pigment locus that allows for black & brown (chocolate/liver) where the brown is a result of black (eumelanin) pigment modification.
This is a very simple gene with just two alleles and dictates the colour of all dark pigmented areas: Nose, eyerims, skin, coat. All researchers agree that the B-b series is very clearcut. Black is dominant to brown.
(B) black: In black (B) dogs the dark pigment will be black. However, this does not mean that the dog's coat will be black. Dark pigment can be restricted by genes in other series. If the dog has a black nose, it is B.
(b) liver: Black pigment is lightened to liver. Anything that would normally be black will be turned brown! So noses and pigment of liver dogs are brown, and if the dog's coat is "genetically black" (see K locus) that will also appear as brown. Like black, the coat of the dog will not necessarily be brown though, the colour may be influenced by other series. Liver (b) being recessive to black (B), two liver dogs cannot produce puppies with black pigmentation. The eye colour of a liver tends to be lighter.
A-locus (Agouti)
The A-locus is a pattern locus. It allows for the distribution of pigment.
There are several allels at the A-locus, these influence the relative amounts and location of red and black pigment in both the individual hairs, and in the coat as a whole.
The most important agouti allels for Chinese Crested, in order of dominance;
(a^y) Sable:
Some solid black hairs intermingled amongst reddish hairs (cream to yellow to red)
(also called a^y-red, agouti-red, non-solid red or dominant red/yellow). Sable colour is a red background and often has black overlay and/or black hairs intermingled amongst hairs of reddish color.
When sable Cresteds are born the black overlay can make them look very dark, in some cases they look black because they are so dark. With age the black hairs fade leaving the red, which often lightens so you end up with dogs of various shades from pale sand to a deep rich red. The shade depends upon how other genes interact with this one. Sable dogs may develop greater or lesser extent of Dark tipping and/or intermixture of Dark hairs with growth of the mature coat.
In some breeds sable is also further divided according to fenotype;
- Red Sable; A sable dog with intense red in the areas without black hairs.
- Cream Sable, often used to describe sables in which all the red is faded to cream/sand.
- Grey sable (or silver sable or grey)
- Black sables are much darker than the averge sable
An example of color changes in a sable dogs from puppy to adult can be seen in the pictures below;
(a^w) Wild Agouti:
Produces the Wolf color, where dark and light colours alternate down the length of the coat hairs.
(a^t) Black & Tan:
This produces a tan-point pattern, which means the dog will be black with areas of tan pigment on the sides of the muzzle, throat, belly, inside the ears, on the chest, over each eye, on all four feet and part of the legs, around the anus and the underside of the tail.
The extent and area of the tan varies and may show in either just one or two of these points or all of them, or could extend beyond them. The depth of pigment also varies and may be as a deep rich tan colour or a very pale cream.
When modified by the gene for white (see the spotting (S) locus) it will produce a tri-colour.
It is suggested that there might be a separate allel
(a^s) Saddle, or alternatively that this might be a variation on Black & Tan : Dark saddle with extensive tan markings on head and legs. Dogs with saddles are often born nearly all black, and the colors continue to come in for the first few years of their life. Individual black hairs are all black, but graying throughout the coat, especially the neck area, can also appear.
E-locus
The Extension Locus is a pattern Locus.
It allows or restricts the extension of dark pigment.
E) Extension Normal:
Full extension of dark pigment as dictated by the A & B locus. This means that any black hairs the dog may have on his coat will be visible. If a dog carries E it will be black coated unless it also carries the two recessive genes for liver, in which case it will be liver coated.
(E^M) Extension Mask:
(e) Extension Yellow:
(also called ee red, recessive red/yellow or true red) Restricts the appearance of any black pigment. This gene only affects black pigment (Eumelanin), not yellow/red (Phaeomelanin) - creating a recessive yellow (red/cream) with no black in the coat. It also means that what could effectively be a genetically black dog can look cream or red. This is the only time that two red/cream dogs can produce a black puppy it means that they are genetically black but the black colour is restricted by the ee.
The skin and eye color generally show through normally but some ee dogs will show reduced pigment on the nose giving the dog what is termed a snow (fades to pink in winter) or dudley (fades to pink all year round) nose. They also seem to be more heavily affected by any gene modifier that reduces pigment.
K-locus (dominant Black)
Until fairly recently, it was believed that the gene for a black coat sat at the top of the Agouti locus. However, recent research has shown this was incorrect, and K has now been designated as the locus.
(K) Dominant Black: This produces a black coat and is dominant to the agouti gene. This means that no matter what a dog may have at the agouti locus, a dominant black will over-ride it and the dog will be black.
(k) Non black: This allele allows the expression of other color/pattern genes to be visible - ie: not hidden by the dominant dark color. Dogs which have two recessive alleles (k/k) can express a variety of phenotypes. All black-and-tan dogs or dogs with tan points are k/k. All fawn or sable dogs are k/k. Cream/red dogs that have an e/e genotype however, could be any genotype at the K locus. Cream/red dogs that have an e/e genotype however, could be any genotype at the K locus.
D-locus
The D locus is the primary locus associated with diluted pigment, which results in coats that would otherwise be black or brown instead showing up as gray, or blue in the case of black, and pale brown or Isabella in the case of brown. The melanophilin gene has recently been shown to be responsible, but not all of the dilute causing mutations have been identified yet.
G-locus (Progressive Greying with Age)
Progressive Graying with age is a pigment locus affecting the intensity of dark pigment. Although only two genes were recognised in this series by Little, this may be a more complex locus, or genes that affect graying may reside at more than one locus. The effect of G, in single or double dose, is the replacement of colored by uncolored hairs as the animal ages, very much like premature graying in human beings.
(G) Progressive Graying with age: The Gaying allel progressively lightens pigment with maturity. (Will fade black to grey/silver). The fading may start immediately after birth or after a period of weeks to months has elapsed. The coat often lightens until the dog is around 2 years, but may also continue through the animal's lifetime.
(g) Normal Dark: This allel has no effect on pigment (neutral allel)
S-locus (Spotting)
The S-locus is a pattern locus, controlling the distribution of white. In the pigmented areas of the coat the dog can be any color as determined by other genes. This locus only controls the distribution of white.
There are four alleles to this gene.The series alleles are listed in decreasing order of dominance;
(S) Solid
(si) Irish Spotting
(sp) Piebald spotting
(sw) Extreme White piebald spotting
All of the spotting genes are assumed to be affected by the action of modifiers, with + (plus) modifiers being generally understood to increase the amount of pigment (decrease white) while - (minus) modifiers being assumed to decrease the amount of pigment (increase white.)
Dogs that have the allels for spotting often have spots in skin in the areas left white by the spotting allel. Often these spots appear gradually, puppies are born with skin pigmented in identical fashion to the coat- then spots will begin to appear in the unpigmented areas of skin, very much like the ticking gene. Nevertheless it is different from the ticking gene, where the spots appear in the coat also, not only the skin.
S) Solid: Self-colour with no white. This is usually the solid coloured dog. However, because of the modifiers it is possible for this allele to also express minor white markings (white toes, white tail tip, or a star or streak on the chest).
(si) Irish spotting: White on muzzle, forehead, chest, belly, feet.
(sp) Piebald spotting: This allows large patches of colour to be expressed. Piebald spotting is a pattern of spots which occur randomly anywhere on the body, including the torso. They are not of consistent size or location therefore. Dogs that have piebald spotting (sp) can have very few colored spots In general, it seems a piebald has more than 50% white, white often crosses the back, and the pattern gives the impression of fairly large colored spots on a white ground.
or very many.
Piebald and irish spotting seem to overlap in phenotype in one direction, while piebald and extreme white overlap in the other.
Although Piebald is sometimes refered to as Harlequin, these era most liekly due to two different genes.
(sw) Extreme White Spotting: Little and others have suggested that there is also an allele, sw, which is the most recessive in the S series that causes "extreme white spotting". iIn an sw dog one would expect to see large amounts of white, with minimal, or no, areas of base color. However, the distinction between a dog with few piebald spots and a dog that is "extreme white" spotted is not that clearcut.
T-locus (spotting)
The character T is an abbreviation of ticking. The gene is not yet demonstrated. Ticking means the appearance of little spots of pigment on white parts of the coat, caused by the dominant T allele. If a dog has t/t it does not have ticking. Some breeds have ticking together with “plating”: big plates of colour. Dogs with ticking have also roan (gray-red) areas.
There are Angyalföldi Kennel's, Arabea Kennel's, DiRabozi Kennel's, Erand Kennel's and Fundoklia-völgyi Kaszanics Kennel's dogs on these pictures.
source:
https://www.chinesecrested.no/en/articles/