BASIC COAT COLOR GENETICS
BACK TO HNR WORKING KELPIES
An Overview


As more research is conducted in the field of (color) genetics, more information gathered and more of the
'unknowns' are 'known' -- this website will be updated to reflect that information.

Definitions:

  • chromosome: The nuclear structure which houses (contains) the genetic information. Chromosomes exist in
    pairs and therefore there are always two copies of a given gene.
  • gene: a unit of inheritance
  • locus (-ci): the position of a gene on a chromosome. Every gene has a specific locus
  • genotype: the genetic make-up of an individual
  • phenotype: that part of the physical appearance of an organism which depends on gene action
  • homozygous: the condition when both alleles of a gene pair are identical
  • heterozygous: the condition when both alleles of a gene pair are different
  • dominant: term describing a gene which can produce a phenotype when present only once; also the
    phenotype which results
  • recessive: term describing a gene which must be present twice to produce a phenotype; also refers to the
    phenotype which results
  • wild: the "normal" phenotype
  • mutant: the non-normal phenotype; is a relative term (relative to the population from which the organism
    originates
  • color genes: genes that affect the pigment color of hairs
  • pattern genes: genes that affect the distribution of a particular color.


Different terms are sometimes used for the same genetic colors, depending on breed and sometimes country too.  
In Dobermans, the dilute brown, is called Isabella.  In Border Collies, the dilute brown, is called Lilac.  In Kelpies, the
dilute brown, is called Fawn. A dog that is genetically 'recessive red' ("e/e") is known as yellow in some breeds and
red in others.  Brown is called chocolate by many and is also referred to as red.  In the ACD breed, the ticked-
black/tan is known as blue.  This is confusing at times.


MELANIN, AGOUTI AND RED:

Melanin is the substance that gives a dog's hair its color.  There are two distinct types of melanin in the dog ---
eumelanin and phaeomelanin.

Eumelanin is, in the absence of other modifying genes, black or dark brown.

Phaeomelanin is, in its unmodified form, a yellowish color.

Melanin is produced by cells called melanocytes. These are found in the skin, hair bulbs (from which the hairs grow)
and other places.  Melanocytes within the hair follicles cause melanin to be added to the hair as it grows. However,
melanin is not added at a constant 'rate'. At the very tip of the hair, eumelanin production is usually most intense,
resulting in the darker tip.

A protein called the Agouti protein has a major effect on the amount of melanin injected into the growing hair. The
Agouti protein causes a banding effect on the hair: it causes a fairly sudden change from the production of
eumelanin (black/brown pigment) to phaeomelanin (red/yellow pigment). An example of this coloration would be like
the color of a wild rabbit. The term 'Agouti' actually refers to a South American rodent that exemplifies this type of
hair.
The Extension Locus - E
This refers to the extension of eumelanin over the dog's body. The dominant form, "E", is normal extension. The
recessive form, "e", is non-extension. When a dog is homozygous for non-extension (e/e), its coat will be entirely
red/yellow (phaeomelanin based). All dogs that have a brown (chocolate) coat will have at least one "E" allele,
because of the production of eumelanin.

The way to tell the difference between an Agouti red/yellow and an Extension (e/e) red/yellow dog -- is the Agouti
red/yellow almost always have some black/brown hair in the coat (usually around the ears and tail) and the
Extension (e/e) dog won't. Another way is the Agouti red/yellow must have at least one ("A^y") allele and can carry at
most one other agouti allele, the Extension (e/e) can carry any two Agouti alleles (not necessarily "A^y").


DOMINANT BLACK -- "K"
The dominant form of black: completely dominates all formation of phaeomelanin pigment. In the past, dominant
black had been placed at the head of the Agouti series (symbol "A^s"). Now, it has been proven to be part of a
separate series, the "K" series, and not at the Agouti locus at all.

Dominant black (K) is epistatic to whatever is found at the Agouti locus (simply means that it causes the Agouti allele
to act differently from what it normally would), however; "e/e" is dominant to "K" at the E locus.

When "K" is in the dominant form, "K/K" or "K/k", there would be no expression from the A Locus and the color is
dependant on what is at the E Locus.  

When "K" is in the homozygous recessive form "k/k", the coat color will depend on what is located on the "E" and "A"
Locus.

Dominant "K" codes for both dominant black and brindle in decreasing order of dominance:

K
-- dominant black (does not allow the A Locus alleles to be expressed)
k^br -- brindle (expressed when A Locus alleles are expressed)
k -- normal (allows the A Locus alleles to be expressed)

A dog that is:

K/K or K/k -- dominant black; dominant black carrying recessive black  
k^br/k^br -- brindled
k^br/k -- brindled, carrying recessive black
k/k -- 'normal' (recessive black)

Brindling is 'stripes' of eumelanin-based (can be modified by the genes at the B and D Locus, so the color could be
black, blue, chocolate or fawn) hairs in areas that are otherwise phaeomelanin based.  In order to produce the
brindle color, at least one parent MUST be a brindle.  Brindle is dominant to its absence, so only one copy is
needed.  If a person has a brindle colored pup for sale and there are no brindle colors anywhere in the pedigree,
then the sire that is reported on the registration papers --- genetically can not be the (true) sire.  There is an
exception to this if the dog is "e/e", he can be a carrier of brindle.  


It is thought that the three loci E, K and A act together as follows:

If the dog is "e/e" at the E locus, and at the K locus, it is "K", "k^br" or "k", its coat will be entirely red/yellow
(phaeomelanin based);

If the dog is E/E or E/e at the E locus, and at the K locus, it is "K/K" or "K/k", its coat will be entirely dominant black
(eumelanin based)
[**NOTE: the phenotypic color will depend on what is at the B, D, C and M Locus];

If the dog is E/E or E/e at the E locus, and at the K locus, it is "k^br/k^br" or "k^br/k" it will be brindled with the color of
the phaeomelanin part of the brindling affected by the Agouti alleles present;

If the dog is E/E or E/e at the E locus, and at the K locus, it is "k/k" the distribution of eumelanin and phaeomelanin
will be determined solely by the Agouti alleles present.
The Agouti Locus - A
Simply, this is how the pigment is distributed on the dog's body and hair shaft.

The Agouti locus controls the formation of the Agouti protein, that in turn is one of the mechanisms that controls
the replacement of eumelanin with phaeomelanin in the growing hair. The alleles of the Agouti locus can affect not
just whether or not the eumelanin -- phaeomelanin shift occurs, but also where on the dog's body this happens.

Two promoters are generally associated with the "wild type" version of the agouti gene.
  • Cycling Promoter
  • Ventral Promoter

The Cycling Promoter produces a banded hair with a black tip and yellow middle over the entire body.  If only the
action of this promoter is disrupted, the hair color on the dog's back will be black and its belly and inside of the legs
will be yellow.  This produces the black and tan color.

The Ventral Promoter dictates that there will be only yellow color in the hair on the belly.  The animal will have black
banded hair on the dorsal (back) side and paler yellow hair on the ventral (belly) side.  If only the action of this
promoter is disrupted, the hair color on the dog will be banded over its entire body.  This is said to be solid agouti
color.

If something inactivates the agouti protein, or if both promoters are disrupted, the animal will appear to be solid
black.

If a mutation occurs at one of these Promoters, this can cause the yellow to be expressed over most of the body.

NOTE:  In part of a series on Dog Coat Color Genetics by Sheila Schmutz, she states that recent studies
show that the agouti signal peptide (ASIP) competes with melanocyte stimulating hormone (MSH), which produces
eumelanin pigments, to bind on the melanocortin receptor and must sometimes win. Both the E allele and Em allele
are responsive to agouti or melanocortin binding in dogs. However dogs that are ee have a mutation in MC1R and
produce only phaeomelanin. The dog's agouti genotype doesn't affect its coat color, which will be some shade of
cream, yellow or red.

To further complicate things, agouti has 2 separate and somewhat distant promoters. Roughly, one seems to
control ventral or belly color and the other dorsal or back color. The simplest way to "see" this is on a black and
tan dog......the back is black from eumelanin pigment being made and the belly is tan or red from phaeomelanin
pigment being made.

The agouti gene has been mapped in the dog and DNA studies to determine which patterns are under the control
of this gene in the dog are in progress. This gene undoubtedly has several alleles, but how many is still an open
question. Some have been identified using DNA studies and tests for agouti phenotypes in some breeds may
become available soon. Although several books attempt to state the dominance hierarchy of the agouti alleles,
since no breed has all the alleles, it is not possible to know this for sure. Most books suggest that it is aw > ay > at
> a. Breeding data and DNA data from our collaborative study with Dr. Greg Barsh's group at Stanford supports
this. However the data confirm pairwise dominance/recessive relationships in different families.......not the entire
hierarchy in one family.


Decreasing in order of dominance:  (**sable may be dominant over wolf in some breeders)

~~ "a^w", 'wolf' color
- This is like "a^y" but the tan is replaced with a pale gray/cream color and the hairs usually
have several bands of light and dark color, not just the black tip of sable. Example would be Keeshond, Siberian
and Norwegian Elkhound.

~~ "a^y", 'sable' - also known as 'dominant yellow' or 'golden sable'. This results in an essentially red/yellow
phenotype, but the hair tips are black (eumelanin). The extent of the eumelanin tip varies considerably from lighter
sables (where just the ear tips are black, called "Clear Sables") to darker sables (where much of the body is dark,
called "Shaded Sables").

~~ "a^s", 'saddle' - Eumelanin is restricted to the back and side regions, somewhat like the black/tan ("a^t") allele
(below).

~~ "a^t", 'tan points' - This is primarily a solid colored dog with tan (phaeomelanin) "points" above the eyes,
muzzle, chest, stomach and lower legs. The hue can range from a pale biscuit to a rich ginger to a golden copper
in color.  Commonly seen in many breeds like hounds, Dobermans, Rottweilers and Kelpies.  In breeds that have
the Irish spotting, along with tan points, this is known as "tri" colored (Australian Shepherds and Border Collies).  

~~ "a" - last of the Agouti series is recessive black. When a dog is homozygous for recessive black (a/a), there will
be no red/yellow (phaeomelanin) in its coat (unless "e/e" is present, which is epistatic to the Agouti series).
Examples of breeds that show to be recessive black are German Shepherd and Shetland Sheepdog.
BLACK or BROWN (CHOCOLATE) - B GENE LOCUS: (pigment color)
This gene, when in the homozygous recessive form, has a lightening effect on eumelanin (black-based colors)
only.  It has no effect on phaeomelanin (red-based colors).

It is believed that the Brown Locus codes for an enzyme, tyrosinase-related protein 1 (TYRP1), which catalyzes the
final step in eumelanin production, changing the final intermediate brown pigment (dihydroxyindole) to black
pigment.  SO, ALL dogs start as BROWN and after the final step --- this directs the color to be black.

When brown (b/b) is expressed, it means that the final step in eumelanin production has not been completed and
the pigment remains brown.  The brown color is not a genetic defect.

When the alleles are in the homozygous or heterozygous dominant form of B/B or B/b, the color and pigment
(nose, eye rims and lips) remains (or directs the color to be) black.

When the alleles are in the homozygous recessive form (b/b), the color and pigment will be brown.  This just means
that the final step in eumelanin production of changing brown to black did not occur.  Phaemelanin (yellow/red
[e/e]) is not affected.  BUT, in the e/e colored dog, if the dog is also b/b; they will be either red or yellow and will
have brown pigment (nose, eye rims and lips).  The pigment granules produced by "bb" are smaller, rounder in
shape, and appear lighter than pigment granules in "B" dogs. The iris of the eye is also lightened.


DILUTION - D GENE LOCUS: (dilution of pigment) Dilute Black   Dilute Brown
This gene has an effect on both eumelanin and phaeomelanin.

When in the dominant form, "D/D" or "D/d", it allows for full color (black or red).

When present in the homozygous recessive form (d/d) it dilutes black (eumelanin) to blue, and red to cream.

COMBINATIONS OF B AND D IN EUMELANISTIC COATS:
The effects of these 2 genes, when combined, form a range of 4 eumelanistic ('black-based') colors:

The color of the pup/dog (Eumelanistic Color):
B/B D/D or B/b D/d will be black in color

B/B d/d or B/b d/d will be blue in color

b/b D/D or b/b D/d will be brown/Chocolate (called red in Kelpies)

b/b d/d will be flat or dull diluted brown/chocolate (called fawn in Kelpies).
WHITE SPOTTING - S GENE: (Kelpies should never have white spotting, a white chest spot and toe tips are permissible)
The "S" series alleles appear to be incompletely dominant. In dogs it is thought there are four alleles that deal with
white spotting:

~~ "S" - 'solid/self color'. Most dogs that are homozygous for "S/S" have no white hair at all, or possible a tiny
amount, like a white tail tip.

~~ "s^i" - 'irish spotting'. This involves white spotting on most parts of the coat, but not crossing the back beyond
the withers.  This color pattern is evident on the Border Collie, Australian Shepherd and other breeds that have the
white collar.  
New research has proven that the white undersides of the Border Collie is dictated by a different
gene.  

~~ "s^p" - 'piebald'. The white is more extensive than irish spotting, and often crosses the back. It is sometimes
confused with the merle pattern.  This coloration usually has large colored spots on the body.  The white covers
approximately 50% of the body.

~~ "s^w" - 'extreme white piebald'. A dog that is homozygous for "s^w" will be almost entirely white, like some Bull
Terriers.  The Australian Cattle Dog, the coloration that is called "Blue" by the ACD breeders/owners, is really the
extreme piebald pattern that is also affected by the ticking gene; giving the coloration a blue appearance.  This
allelic pair is also responsible for the "color headed" white dogs.  Often times, along with a colored head, there will
also be a colored spot near the tail.


TICKED - T GENE:
A dominant mutation that causes the presence of color (flecks of color) in areas that have been made white by the
effect of alleles in the white spotting (S) series.

Ticked ("T/T") is incompletely dominant to non-ticked ("t/t").   
ALBINO - C GENE: (development of pigment)
The intensity of melanin production in the coat hairs is affected by this gene. The dominant form, "C", is termed 'full
color'.

At this locus, almost all dogs are "C/C", or full color.

The lower series alleles, in order of decreasing dominance:

~~ "c^ch" - Chinchilla -- It is an incomplete dominant gene.  Chinchilla lightens most or all of the red/yellow
(phaeomelanin) with little or no effect on black/brown (eumelanin). It turns black/tan to black/silver.  In dogs, this
gene lightens yellow, tan or reddish phaeomelanin to cream.  Since there is little effect on the dark eumelanin,
phaeomelanin is effected more strongly than eumelanin and brown.  Dilute eumelanin (blue) is effected more
strongly than dark (black) eumelanin.  When chinchilla is present, it dilutes brown to milk chocolate, blue to silver
and red to a butter cream color.

NOTE:   Newer research indicates a chinchilla-like mutation occurs in dogs, although, tyrosinase activity hasn't
been shown to be connected. Therefore, some other factor may be involved and the dog chinchilla allele may not
belong in this series. Also, there may be more than one form of the chinchilla gene.

~~ "c^e" - is 'extreme dilution'. It causes tan to become almost white. It is thought that the white labrador might be
"c^e" with another, lower, "C" series allele. The "c^e" allele may be responsible for producing white hair, while
allowing full expression of dark nose and eye pigment.  West Highland Terriers are thought to be e/e c^e/c^e.

~~ "c^b" - or blue-eyed albino. This is an entirely white coat with a very small amount of residual pigment in the
eyes, giving pale blue eyes. It is also called platinum or silver.  This allelic pair could be responsible for the white
coated, pink skinned, blue-eyed Doberman's.

~~ "c^c" - true pink-eyed albino. Has not been seen in dogs.


GRAYING - G GENE:
This is a dominant mutant gene that causes the dog to gray with age. The pigmented hairs are progressively
replaced with unpigmented hairs.
MERLE - M GENE: (Kelpies do not have the merle pattern)

The only way a merle colored pup can be produced is if at least one parent is merle.  Some breeders are of the
understanding that the merle gene is a recessive gene and is carried from generation to generation.  This is not
correct.  The merle gene is not carried, meaning -- the dog is either a merle or is not a merle.  There are no
exceptions to this law of genetics (for now, at least, until further research is conducted).

If someone tells you that they have a litter of merled colored pups and there are no merles for many generations in
their bloodlines --- then these merled pups were not sired by the sire the owner thinks there were. In fact, he
should look for the hole in the fence!  

The merle gene is an incomplete dominant or a gene with intermediate expression and is another dilution gene.
Instead of diluting the whole coat it causes a patchy dilution, with a black coat becoming gray patched with black.
Brown becomes dilute brown patched with chocolate, sienna, brick, and various diluted brown colors.  While sable
merles can be distinguished from sables, this is sometimes very difficult because the merle coloration looks like --
to just slightly different from -- the sable color. The merling is clearly visible at birth, but may fade to little more than
mottling of the ear tips as an adult. Merling on the tan points of a merle black and tan is not immediately obvious,
either, though it does show if the mask factor is present. Eyes of a merle dog are sometimes blue or marbled
(brown and blue segments in the eye).

A
"m/m" (homozygous recessive) dog is normal color (no merling). A "M/m" (heterozygous) dog is a merle. A
"M/M" (homozygous dominant)
dog, known as a double merle (from a merle to merle mating), has much more
white than is normal for the breed and may have hearing loss, vision problems including small or missing eyes, and
possible infertility. The health effects seem worse if a gene for white markings is also present. In Border Collies and
Australian Shepherds, all of which normally have fairly extensive white markings, the "M/M" white has a strong
probability of being deaf or blind. A "M/M", double merle, to "mm", non-merle black in color breeding, is the only
one that will produce 100% merles.

Cryptic or phantom (as it's sometimes called) merles are dogs which carry a merle gene but are phenotypically
(look like) tri, bi or self colored. These dogs will have some small area of merling somewhere, usually a tiny patch of
merle pattern on their ear, tail, top of head, etc. Keep in mind the tiny patch can be only one hair and it can be
located anywhere on the body. Cryptic merles are very rare. AGAIN, a cryptic or visible merle can only be produced
when one or both parents are merles.
GENOTYPES AND COLORS: ("-" is either the dominant or recessive allele)
  • B/- D/- E/- K/- = black
  • b/b D/- E/- K/- = brown (chocolate)
  • B/- d/d E/- K/- = blue
  • b/b d/d E/- K/- = fawn

AGOUTI:
  • at^at B/- D/- E/- k/k = black with tan points
  • at^at b/b D/- E/- k/k = chocolate with tan points
  • at^at B/- d/d E/- k/k = blue with dilute tan points
  • at^at b/b d/d E/- k/k = fawn with dilute tan points

NON-EXTENSION RED (cream):
  • B/B d/d e/e = dilute red to pale cream with gray nose (dog is genetically a
    dilute black, but will be a cream color)
  • B/b d/d e/e = dilute red to pale cream with gray nose (dog is genetically a dilute
    black, but will be a cream color)
  • b/b d/d e/e = dilute red to pale cream with rosey-brown nose (dog is genetically
    dilute brown, but will be cream color)
  • b/b D/d e/e = dilute red to pale cream with brown nose (dog is genetically
    brown, but will be cream color)
  • b/b D/D e/e = dilute red to pale cream with brown nose (dog is genetically
    brown, but will be cream color)
  • B/B D/D e/e = dilute red to pale cream with black nose (dog is genetically black,
    but will be cream color)
  • B/b D/d e/e = dilute red to pale cream with black nose (dog is genetically black,
    but will be cream color)