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Genetics of
Dresses
Extension Gene (E)
The Extension gene is the gene responsible for the basic Black & Chestnut coats.
The dominant form is denoted by E
The recessive form is denoted e
When the dominant allele E is present, melanocytes have eumelanin production. The horse then has a dark coat. Conversely, when only the recessive allele e is present, there is an absence of production of eumelanin, the horse therefore has a light coat.
Gene Agouti (A)
The Agouti gene, when it is dominant A, is characterized by dark ends (hair and limbs), that is to say by the production of eumelanin only at these points. The horse therefore has an uneven coat. When it is a recessive, if it is present in two copies, it is expressed by a uniform coloring of the coat: high production of eumelanin in the melanocyte.
Thus, the presence of the A allele will transform the Black into Bai.
Gene Cream (Cr)
It dilutes the dress of the wearer and if it is homozygous (CrCr) his eyes are blue. The Cream gene in a single copy gives the dresses: Palomino, Smocky Black and Isabelle, in two copies, these are the dresses: Cremello, Smocky Cream, Perlino.
Dun Gene (Dn)
The Dun gene is a dominant dilution gene responsible for so-called “wild” coat colors in horses. Its action gives primitive marks, classically welts on the legs and a mullet stripe, more rarely a crucial band crossing the shoulder, in addition to discolouring the dress. Among the dresses concerned there are: Chestnut Dun, Grullo, Bai Dun, Dunalino ...
Silver Gene (Z)
It is a dominant gene which is found quite often in AMHA and which acts on the black pigment giving it a silvery appearance. It therefore does not act on the basic Chestnut dresses. Silver also adds small, lighter dapples to the coat from time to time, hence its English name of " Silver Dapple ". In addition to this action on the coat, the gene acts in the eyes and causes multiple congenital eye abnormalities ( MCOA ) more or less severe, depending on whether it is present heterozygous or homozygous. Some anomalies are identifiable thanks to a thorough ophthalmologic examination but it is still more careful not to cross two Silver horses together .
Champagne Gene (Ch)
It is quite rare and gives clear eyes, speckled mucous membranes and a diluted coat. The variations of Champagne range from beige to orange depending on the base color that it dilutes.
Roan gene (Rn)
It is characterized by the presence of white hairs, in greater or lesser quantity, in the coat of a horse. In the majority of cases, the white hairs do not affect the horse's hair, head or limbs. It is an evolving dress over the seasons. According to some theories, it would be risky to cross two Roan horses because the foal could be born homozygous or that would be lethal. However, this is only a theory that has not yet been verified, as research on this subject is still in progress.
Gray Gene (G)
The gene Gray is a dominant and progressive gene. Foals are born with a non-gray coat and their hair will first darken and then gradually lighten, until they obtain a white phenotype.
All coats undergo the graying process if the horse has at least one G allele.
Graying manifests itself with age, more or less rapidly depending on the individual. Depending on its basic coat, the horse will go through a multitude of colors, embellished with pommelures, marks, or speckles. At the end of the graying process, the horse will be all “white” to the point that we can no longer distinguish its white markings (list, balzane, magpie spots).
Gene Tobiano (To)
The Tobiano is phenotypically characterized by the presence of white patches distributed vertically, and four white legs, the colored parts being generally on the flanks and the chest, round or oval in shape, with sharp edges. It can be added with other forms of magpie coats, and with dilution genes. Like any pie gene, it can have minimal expression ; the horse is united with balzanes only for example, as a maximum expression with a very largely white horse.
Gene Lethal White Overo (Lwo)
Gene characterized by large white markings associated with a darker coat color. Unlike those of the Tobiano which are rather rounded, the white spots of the LWO have jagged and irregular contours. When present in duplicate (homozygosity) Lethal White Overo is responsible for white foal syndrome ; a genetic anomaly which causes the death of the foal in the hours which follow its birth. It is therefore imperative to know if a horse is wearing the LWO so as not to cross it with another LWO.
Splashed White Overo Gene (Swo)
Also called Balzan, Splashed White Overo is known to give localized white spots on the lower parts of the body and head. The gene is genetically linked to the overo coat family. It is characterized by pink skin and white spots on a darker colored coat. Many SWO horses have faint markings, while others appear to have 'been bathed in white paint'. Blue eyes are characteristic of this dress. There are 3 forms, SW1 being the most common. Some studies tend to conclude that SW2 and SW3 would give rise to non-viable embryos if the latter are homozygous. The marriage of these two forms is therefore not recommended.
Sabino gene (Sb)
The Sabino is part of the overo dresses, it is characterized by the presence of letterhead and balzane markings as well as numerous white hairs on the body. The horsehair can also be white or sparse.
Leopard Complex Gene (Lp)
Leopard Complex , also mistakenly called Appaloosa coats, is a genetic mutation that results in a group of coats characterized by small round spots of light or dark color. The mutation which is at the origin seems very old. In addition to coat color, the LP gene is responsible for ridged hooves, apparent eye sclera, and mottled skin. The dresses of the leopard complex are available in leopard, cape, few spot, varnish and frost. They can be the cause of a genetic disease of the eye and sight.
Gene Sooty (Sty)
The Sooty gene is noted STY when the allele is present and sty when it is absent. The actions and mechanism of this gene are not yet all known, but we know that it darkens the horse's coat and causes black hair to appear in the horse's coat, more or less depending on the case. It is a priori evolutionary gene, which varies not only over the years but also over the seasons. It can also bring pommelures or even marbling depending on the case.
Flaxen gene (F)
The Flaxen gene is a dilution gene that discolors the hair of the coat of the chestnut horse, resulting in a phenotype called the washed-hair sieve. Still unidentified, it is presumed to be recessive and it acts only on the chestnut pigment, giving blond hair, whether it is a classic chestnut or a burnt chestnut. The Flaxen gene should not be confused with the Silver gene, which acts only on the black pigment, nor with the palomino which is due to the Cream gene.
