FAQ about Homozygous Black
Every horse is born with a "base" color to his coat, either Red (e) or Black (E). The Red gene is always recessive to the Black gene. Red horses (chestnuts and shades of chestnuts) are known to be homozygous for Red, because the chestnut gene is recessive, and therefore requires two copies of the Red gene to show red as the base coat color.
Gray is NOT a base coat color.
Think of it as if this were a human - we are not born gray, we just turn it as we age. We have our base hair color (blonde, brown, black) and then Old Man Age shows up and we turn gray.
Therefore, a horse that is homozygous or heterozygous for Red or Black can also be gray.
Black is a dominant base coat color. Black can be either heterozygous (Ee) or homozygous (EE). Heterozygous blacks can produce horses that are red or black in base coat color. This means, the horse carries one Black gene and one Red gene. Since Black is dominant over Red, the horse appears with a black base coat color (black, bay, brown). When a heterozygous Black horse is bred to a Red horse, he can produce a Red horse. Two Heterozygous blacks can also produce a Red, if each passes on their red gene. This is why you can breed a bay to a bay and still get a chestnut.
A homozygous Black can only produce black or shades thereof (black, bay, brown).
Remarkable is a Homozygous black, meaning there was no Red detected in his DNA. He can be assumed to be homozygous for black pigment (EE). It cannot have red foals, regardless of the color of the mare. The basic color of the horse will be black, bay, or brown, but depending on genes at other color loci, the horse may be buckskin, zebra dun (this I would like to see!), grulla, perlino, gray, white or any of these colors with the white hair patterns tobiano, overo, roan or appaloosa.
Being a Gray, he will pass the graying on to 50% of his foals. All offspring however will have the base colors as mentioned above.
Dun vs. Buckskin
Dun and buckskin are used rather messily to refer to horses with light red- yellow, yellowish or sandy bodies, with or without black points (mane/tail/legs/ears), with or without dorsal stripes. (Darker bodied horses are called bays if they have black points, and chestnuts or sorrels if they have non-black points.) However, there is a lot of disagreement about the two terms.
In the past, buckskin registries have referred to darker shades as buckskin and lighter ones as dun, while geneticists usually called buckskin the lighter shade. Another definition sometimes used was that buckskin horses have black points, and duns have brown or light points. Various registries and dictionaries have defined one or the other as having a dorsal stripe. The AQHA has sent out an advisory to its members that they have a new definition of dun and buckskin, to whit: duns have dorsal stripes, buckskins do not. Apparently, they are revising new registrations to reflect this new definition.
The following is a compilation of information from the books "Horse Color" and "The Horse", along with help from the net.
clear light yellow, tan, sandy, & dark cream horses with *black* points and *without* a dorsal stripe. This is the definition that was used in the old American West. (Genetically buckskin is a cremello-dilution of bay.)
: This is a larger category. It includes:
a) yellow/tan horses with *black* points, *with* a dorsal stripe (Genetically a dun-dilution of bay.)
yellow/tan horses with *non-black* points, with or without a dorsal stripe. (In practice these horses usually have a dorsal stripe anyway.) The dorsal stripe can be any shade. (Genetically a dun-dilution or a cremello-dilution of chestnut.)
Note that yellow/tan horses with *black* points are buckskin if they don't have a dorsal stripe, and dun if they do. (To remember this, think of "buck skin" -- deer don't have dorsal stripes. Or think of D=dun=dorsal.) Horses with yellow/tan coat colors and *non-black* points used to all be called "duns" regardless of the stripe. However, the new AQHA rulings mean that horses with non-black points without the stripe will be called buckskin rather than dun.
The body color can be of different shades. For horses with *black* points, without dorsal stripes (if the horse has a stripe just change "buckskin" to "dun"):
Dark or smokey buckskin
= head and neck and rump a very dark brown, with more yellowing on the belly. (Caused by black hairs being mixed in with the yellow, the smutty Sty gene.) Definitely not grulla. Called "coyote dun" if there's a dorsal stripe.
Dusty buckskin = yellow-brown body color.
Peanut butter buckskin-just like it sounds-sort of a orange-tan buckskin with black points.
Golden buckskin = the classic golden color with black points.
Oatmeal buckskin = a shade just lighter than golden, with darker hairs on the rump and neck. But it isn't oatmeal color at all. ("Zebra dun" if striped.)
Silver or creamy buckskin = very pale gold, almost cream body color, with black points.
For horses with *non-black* points:
Lilac dun -- an unusual rosy color with brown points, hazel eyes, and no dorsal stripe. (Cremello-dilution of a chocolate brown horse.)
Muddy dun -- pale brownish red with brown points and head, and a brown stripe. (Dun-dilution of a chocolate brown horse.)
Red dun -- very washed out red or yellowish-red bodies with brown, red or flaxen points. Usually with dorsal stripe. The legs and head are usually a darker shade of red than the body (unlike sorrel, which can have the same body color but pale legs. Also a sorrel wouldn't have a dorsal stripe). Variations in body shade are called "orange dun", "apricot dun", etc.
Yellow dun -- yellow/tan body with non-black points. May have dorsal stripe, or may not. With brown points, often called "claybank dun".
Palomino -- yellow body with cream or white points. Technically this is a type of yellow dun. "Isabella" is a very pale cream palomino. "Sooty palominos", also called smutty palominos, have dark hairs mixed in with the yellow, giving a deep burnished look (due to the action of the smutty gene, Sty). In Europe people sometimes use "isabella" for all palominos. Palominos are called "bright chestnut" in some breeds (Arabian). Information found at Daily Post/ search Asaddlery.