Colour Genetics

BASIC COLOURS

RED AND BLACK:

All horses are either BLACK (E) or RED(e).
“E” is dominant and “e” recessive. Therefore, E/e or E/E means the horse will look black, and the only way a horse will look entirely red is with the genetics e/e. An E/e black horse can throw a red foal if the other parent also has an e (e/e or E/e).

AGOUTI GENE:

If a black horse has an Agouti gene (A), then that horse will only show their black colouring on their mane and tail.   “A” is dominant to “a” (no agouti gene). This effect can only be seen with black (EE or Ee) horses, red (ee) horses aren’t affected by the agouti gene, but a red horse can can be a carrier of the “A” gene and give it to its foals.

DILUTION GENES

CREAM GENES:

This is considered a desirable gene. The cream gene is neither dominant nor recessive – instead it is an “incomplete dominant” gene. A black horse with two copies of the E gene (E/E) is still just a black horse, the same as a black horse with one copy of the E gene (E/e). But with the cream gene, if a horse has two copies of the gene then it gets double the effect of the gene.  A horse with one copy can be referred to as a single dilute (n/Cr), and a horse with two copies can be called a double dilute (Cr/Cr). The cream gene affects both black and red horses, but if affects them differently. See the chart below:

No Dilution (n/n)Single Dilute (n/Cr)Double Dilute (Cr/Cr)
Red (e/e)PalominoCremello
Bay (E/e or E/E with A/a or A/A)BuckskinPerlino
Black (E/E)Smokey BlackSmokey Cream

PEARL:

The Pearl gene (Prl) is a recessive gene, which means, like the “e” gene, it is only seen if the horse has either two copies of the Pearl gene (Prl/Prl), or if the Pearl gene is inherited along with a cream gene (Prl/Cr). A Prl/Cr horse has similar colouring to a Cr/Cr horse, and both of these genetic types are referred to as a “double dilute”.  Refer to the table below:

No Dilution (n/n)Single Dilute (n/Prl)Double Dilute (Prl/Prl)
Red (e/e)No change in colourPalomino Pearl (Pale palomino coloured body with a nearly white mane and tail)
Bay (E/e or E/E with A/a or A/A)Perlino (Apricot body with coffee brown coloured mane and tail)
Black (E/E)Smokey Cream (Apricot colour)

SILVER:

The Silver gene (Z) is a dominant gene but, like the Agouti gene, it only affects black horses. Because it is a dominant gene, the effects of this gene can be seen even if the horse only has one copy of the gene (Z/n). If a black horse has a Silver gene, that horse will have a chocolate brown body with a flaxen mane and tail.  Their chocolate brown body may express dappling. If a horse with a silver gene also has the agouti gene, then that horse will have lightened lower legs and a flaxen mane and tail. A red horse may carry a silver gene and give it to its foals, but you will not be able to see the effects of the silver gene on the red horse. A negative effect of this gene is the side effects it can have in the horse’s eyes. These effects are referred to as “multiple congenital ocular anomalies (MCOA)” and can include many issues including blindness due to retinal detachment.

DUN:

Dun (D)  is also a dominant gene. The Dun gene affects both blacks and red horses. Horses that carry the Dun gene (D) have a distinctive darker stripe down the back and darker legs, face, mane, and tail.   They also exhibit faint horizontal darker stripes on the backs of their legs. Refer to the table below:

Red Horse (e/e) Plus the Dun gene (D/d or D/D)Red Dun
Black Horse (E/e or E/E) Plus the Dun gene (D/d or D/D)Blue Dun, also known as Mouse Dun or Grullo/Grulla
Bay Horse (E/e or E/E and A/a or A/A) Plus the Dun gene (D/d or D/D)Classic Dun also known as Bay Dun or Zebra Dun

GREY:

The Grey gene (G) is a gene that slowly removes the colour from a horse over years.  The grey gene is not a base colour (like Red or Black), nor is it a dilution (like Cream or Pearl). This loss of colour can be a uniform loss of colour, or can result in a  “fleabitten” pattern (small darker spots), or a “mottled” pattern (lighter splotches) before the colour fully fades. Horses with the Grey gene are at a higher risk of getting melanoma than other horses.

PATTERNS

TOBIANO:

The Tobiano gene (T) is a dominant gene, so the horse only needs one copy of this gene to express this pattern.  Tobiano horses have areas of colour, traditionally a “shield” on the chest and on the rump on a white background. Generally, all four legs are white, at least below the hocks and knees.  The head markings are like those of a solid-colored horse–solid, or with a blaze, strip, star or snip. A horse with the tobiano gene may be either predominantly dark or white. The tail is often two colors.

Homozygous tobiano horses (horses with two copies of the tobiano gene – T/T) often have “ink spots” or “paw prints”,which are small areas of dark colour with halos them that can be seen on the horse’s white background.

Black horses (E/e or E/E) that have the Tobiano gene (either T/t or T/T) can be referred to as Piebald horses.

Red horses (e/e) that have the Tobiano gene (either T/t or T/T) can be referred to as Skewbald horses.

Bay horses (E/e or E/E with either A/a or A/A) can be referred to as Tricolour horses.

ROAN:

The Roan gene (R) is a dominant gene that is commonly confused with the Sabino 1 and the Grey gene, but is a pattern of individual white hairs sprinkled evenly into the body of the base colour of the horse, rather than a pattern with distinct white areas.  A negative phenomenon of the Roan gene is that if the horse inherits two copies of the Roan gene (R/R), then it will most likely die. There are only a few R/R foals that have lived.

FRAME OVERO:

The Frame Overo gene (O) is an incomplete dominant gene.  A horse with the Frame Overo gene expresses their base colour along the their topline, running from their wither to their dock with irregular, jagged white markings that run underneath the horse’s frame along the horse’s ribs, neck, and belly.  They also usually have large blazes on their face. At least one of their legs will be dark, although often all 4 feet are dark (whereas Tobiano horses usually have white legs). There is not usually white on the topline of the horse (again, unlike Tobiano horses).  The tail is usually one colour. Again, a negative feature of the Frame Overo gene is that horses that inherit two copies of this gene die, usually within a week of birth. This is referred to as Lethal White Syndrome (LWS).

LEOPARD PRINT/APPALOOSA/PATTERN 1:

A horse with the Leopard Print gene (LP) will have light/dark mottled skin around the nose, lips, and genitals, with striped hooves. A horse that has two copies of the Leopard Print gene (LP/LP) has increased risk of CSNB (Congenital Stationary Night Blindness). If a horse has both the Leopard Print gene (LP) and the Pattern 1 gene (PATN1) then those horses will express more white.  Refer to the table below:

One copy of the Leopard Print gene (LP/lp) without the PATN1 geneBlanket Appaloosa (white spots on the bum of the horse)
Two copies of the Leopard Print gene (LP/LP) without the PATN1 geneSnow Cap Appaloosa (mainly white bum of the horse)
Either one or two copies of the PATN1 gene (PATN1/n or PATN1/PATN1) without the LP gene (lp/lp)Solid horse with no pattern that can be seen, but PATN1 can be passed to offspring
Pattern 1 gene (PATN1/n or PATN1/PATN1) plus one copy of the LP gene (LP/lp)A mainly white horse with a lot of spotting
Pattern 1 gene (PATN1/n or PATN1/PATN1) plus two copies of the LP gene (LP/LP)A mainly white horse with a few spots

SPLASHED WHITE PATTERN 1/2/3: SW1/SW2/SW3:

The Splashed White genes are a group of incomplete dominant genes. Many splashed white horses have a large blaze, extended white markings on legs, with some white spotting on their belly, and they usually have blue eyes. However, sometimes, the white areas are quite small and cannot be distinguished from horses with other patterns that exhibit white areas. The classic look of a horse with a Splashed White gene is that they look as though they were dipped in white paint, feet first. Their head, legs and belly may be white, sometimes connected to a patch running up either side of their body. The outer edge of these white markings are crisp and well-defined.  Horses that have two copies of either the SW2 or the SW3 gene will not survive, as these combinations are fatal, and a white inner ear could denote deafness.

DOMINANT WHITE:

There are 20 different Dominant White genes that can be inherited in horses, but the one most commonly found in Gypsy horses is the W20 gene. A horse that has the Dominant White gene (W20) and another pattern will exhibit more white than the other pattern would normally show.  A horse with no other pattern and only the W20 gene will only show a minimal white pattern. This is one of the only patterns that will usually leave the eyes of the horse a dark colour.