White Pattern Horses
Many horses exhibit white markings, which can vary dramatically amongst different specimens. White markings are not considered a true horse 'colour' rather they are a lack of colour where pigment has been lost. These traits are genetic, and there are many different genes which cause whiteness, to widely varying degrees.
In many cases, where a horse has not faded to pure white, its original base colour is visible in patches, such as in the case of the Tobiano horse shown beneath. The Tobiano gene specifically distributes the white markings giving the effect shown, of course as with all genes there are variations of how the white markings are expressed - but there is a general defined pattern for Tobiano specimens.
This horse is a black Tobiano, or Piebald. Not a white horse with black markings. It's base colour is black, the white markings are secondary, caused by a dominant gene.
The same is true in the case of 'spotted horses', except whereby the white is expressed in such a way it sometimes gives a false appearance that it is the main colour of the horse. In actuality, the horse's base colour is only just visible in small 'spots' where the white has not occurred.
In the case of this Appaloosa spotted horse, it may appear that the horse is white, with black spots, but it is in fact a black/brown horse, with white covering.
White may be considered a cover, rather than a colour.
As already mentioned, the various genes which cause colour-loss (white) have varying wide-ranging effects. The dominant genes responsible for Appaloosan spotted specimens have varying impacts across the breed, some horses have more pigmentation loss than others, hence few-spot Appaloosas. Some horses also carry the Grey gene, which causes extensive fading and in most cases leaves the horse almost pure white.
Genes responsible for white:
- Frame Overo. - Also linked to Lethal White Overo syndrome.
- Tobiano (highly desirable pattern) as seen above.
- Splash Overo Linked to belly-splash and white on lower legs and underside of horse.
- Grey. 'Fading gene' seen across a variety of breeds. Can lead to full pigmentation loss, and pure-white horses.
- Appaloosa 'spotting' genes (Varying effects throughout the breed type, as yet not genetically mapped for DNA identification)
-Sabino Varying effects, many small areas of 'roaned' white are due to the presence of Sabino. Maximal Sabino horses are usually pure white in appearance.
Genes marked in blue are detectable using DNA testing and are amongst Animal Genetics wide-range of horse DNA tests.
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