|Yes, this horse is real. Can I have one please?? This silver dapple horse is SC Code Of Honor, a Rocky Mountain Horse stallion (pic linked through from here).|
When a horse or pony inherits either one or two copies of a rare version of the PMEL17 gene (melanocyte 17 precursor gene) known as silver, it alters the production of black pigment in their coat in an analogous manner to the way cream alters the production of red pigment. The mane and tail of the horse become a cream or silver colour, while the short hair on the body is only slightly affected. Simple concept, amazing result.
As I've said in all these horse genetics articles, the important things to remember when discussing genes are:
- Your horse has two copies of each gene*, one inherited from either parent;
- There are many different versions of each gene in the horse population, some of which can produce identical or nearly identical appearance and biological function, while other versions can produce a different coat colour or cause disease; and
- Each physical characteristic of your horse, including coat colour, results from the combined effects of the two copies of each gene, AND the interactions between a large number of different genes.
|I did not know that bay silver could be soooo good-looking. Meet Kelsie Park Mirinda - what a glamour!|
So far, so good, or at least so gorgeous.
The tricky bit is that when silver interacts with a basic coat colour of chestnut, you get chestnut. "What?", I hear you say. But yes, it's true: with no black pigment to act on, there is no change to the colour. Chestnut plus silver equals chestnut. The family silver hasn't exactly been stolen though, just hidden. A chestnut with the silver gene can pass it on to their own foals.
So is there any difference in appearance between a horse or pony with one copy of the silver gene and one with two copies? I can't find anything definitive, but image searches suggest that there is no obvious difference. If you want to know, genetic testing would be the quickest way to find out.
|Eye abnormalities and the silver coat colour. Follow this link to see the full description of the eye abnormalites illustrated in part A and part B.|
at this miniature mare's left eye. This bulging eye is an obvious
outward indication of extensive eye abnormalities caused two copies of
the silver gene. Picture linked from here (warning, image is part of a series than includes dissection of the eye). |
|A sweet silver dapple foal with her gorgeous silver dapple mother (pic linked through from here).|
Do you want to know if your horse has one or two copies of the silver gene? At Practical Horse Genetics we are currently working to add this test to our repertoire and it should be available shortly.
* Except for genes on the X and Y chromosomes in male horses, where there may be only one copy.