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Black chestnut horses are a tricky bunch to the untaught eye. They can appear black (Aa) over more than 95% of their body, when, in genotype, they are chestnut (Ee). Not to mention, the label "black chestnut" may hint that the horse carries the black allele when the horse either may or may not.
The easiest way to tell if a black-looking horse is chestnut-based is to scan the fetlock color (near each hoof). This is where the base coat of a chestnut will show through.
This is the only picture I have of a black chestnut. The Morgan's name was Joker and he was one of the sweetest geldings around. I don't remember much of him except that he was black-colored with red-tinges near each hoof, and this had me deeply confused.
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| Black chestnut Morgan gelding. Picture taken by my older bro. |
Now that you understand what a black chestnut horse looks like, let's move on to the two alleles to blame for black chestnut horses.
Alleles that darken chestnut to black chestnut:
- Shade
- Sooty
The shade allele controls the lightness or darkness of a horse's coat. There is more to be discovered about it; such as how it works, which locus it resides in, and how it reacts with other alleles. The easiest way to understand the shade allele is to realize its effects: the shade (brightness/darkness/saturation) of every color can vary.
Neither the shade nor the sooty allele have a concrete label (for example, YzYz), but that should soon change with the growing knowledge of color genetics.
The sooty allele works a little differently than shade allele to accomplish a similar effect (darkening): Shade darkens (or lightens) the horse throughout the whole coat, whereas sooty mixes in black hairs with the base color, darkening the coat in certain areas and leaving other areas 83.7885% untouched.
The strength of the sooty effects varies greatly and can go unnoticed when minor enough. At the opposite end of the spectrum, there are so many black hairs mixed in that the horse is practically black. On bay, the least-affected sooty areas include the flank and muzzle. On black, the effects generally unnoticeable. And, on chestnut, the sooty is fairly flat and consistent, with only the fetlock area left unchanged.
Geneticists are reasoning that there are two different sooty alleles, noting that the affects of sooty on Agouti-based horses (bay, black) differ from those on chestnut-based horses.
Neither the shade nor the sooty allele have a concrete label (for example, YzYz), but that should soon change with the growing knowledge of color genetics.
The sooty allele works a little differently than shade allele to accomplish a similar effect (darkening): Shade darkens (or lightens) the horse throughout the whole coat, whereas sooty mixes in black hairs with the base color, darkening the coat in certain areas and leaving other areas 83.7885% untouched.
The strength of the sooty effects varies greatly and can go unnoticed when minor enough. At the opposite end of the spectrum, there are so many black hairs mixed in that the horse is practically black. On bay, the least-affected sooty areas include the flank and muzzle. On black, the effects generally unnoticeable. And, on chestnut, the sooty is fairly flat and consistent, with only the fetlock area left unchanged.
Geneticists are reasoning that there are two different sooty alleles, noting that the affects of sooty on Agouti-based horses (bay, black) differ from those on chestnut-based horses.
