Grey and Roan
This page is under construction. It will contain extensive information on the horse colours Grey and Roan. We are looking for pictures of solid coloured horses that are representative of the various shades in each colour. For a photo to be chosen the horse must be clean, unclipped, and standing in a conformation type stance that best shows off the colour. Ideally photos of Grey horses will show a progression over the years. Ideally Roan horses should show differences in summer and winter coats.We have provided information on these colours in an unfinished format for your initial learning enjoyment, with more to follow as the page evolves.
Modifier Genes: Genes/alleles that modify areas of a horse’s body coat, mane, tail and skin with various shapes of white depigmentation, also known as pattern genes. Red (ee) based horses tend to show more white than Black (EE, Ee) based horses. Grey and Roan are still classed as modifier genes even though they both present as a difuse scattering of white hairs throughout the coat.
Grey (G): a dominant gene that is considered the strongest of all coat modifiers. It removes colour pigment from a coat in a gradual and progressive depigmentation (fading) of the horse. Only one allele is required to cause greying but it is felt that the homozygous form will turn Grey faster. A foal can be born any colour and any pattern prior to turning Grey. The foal often has a darker, more mature coat colour at birth (hyperpigmentation) and can develop “goggles” around the eyes as the first step in the greying process. Hyperpigmentation can also occur in an older horse causing it to appear to darken before becoming lighter, creating the old belief that all Grey horses started as Black. Greying usually starts on the head and can be as subtle as a few white hairs around the eyes and muzzle. Grey also tends to lighten the tail end near the beginning of the process. The mane, top of the tail and lower legs are generally the last areas to turn white. As a horse Greys the coat colour can be labeled with many term such as steel grey, dappled grey and rose grey, however the horse will not stay this colour but will continue to fade. Greys lighten to one of two forms: almost pure white or “flea-bitten” which is Grey with tiny non faded spots of colour. The skin of a Grey horse usually remains its original colour but sometimes it can fade as well. Melanomas occur in close to 80% of grey horses over the age of 15 years, usually under the tail or around the ears. Most Grey horse melanomas are benign (not cancer) and are not caused by sun exposure but by an over expression of both the STX17 gene and neighbouring NR4A3 gene.
Genetics: The Grey gene, STX17 (Syntaxin 17) is located on chromosome 25 and has 7 exons.
NCBI: Gene ID: 100054797; Location: Chr 25 NC_009168.2 (6531273…6588557); Length: 57,285 bp
Ensembl: Gene ID:ENSECAG 00000015108; Location: 6531290…6582662; Length: 51,373 bp
Roan (Rn): produces a coat pattern that has white hairs mixed in with the horse’s base colour, creating a horse that resembles a Grey to some extent. For the first few years of a horse’s life it will lighten until it reaches a certain point. The horse will not lighten to white, there will always be the base colour mixed with the white hairs. The head and points are usually noticeably darker than the rest of the body with fewer Roan hairs mixed in. A Roan can often seem to change colour seasonally as well, appearing lightest in the spring and darkest in the winter. This lighter/darker effect is caused by the outer darker guard hairs shedding first before the lighter roan undercoat. The summer guard hairs are also dark but not as long as winter ones so the summer coat does not appear as dark as the winter coat.
Genetics: The gene for Roan has not been identified as this time, but appears to be linked to the MC1R gene (extension) and the KIT gene (white spotting). Many people have come to believe that Roan is located on KIT but this has not been proven scientifically.
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