Horse Color Basics + Champagne

Note: for those interested in an in-depth explanation of the technical aspects of the champagne mutation, see this PDF by Deborah Cook, Samantha Brooks, Rebecca Bellone, and Ernest Bailey, working out of several different universities: CLICK HERE

added Monday, November 06, 2017

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Genes

All characteristics, including color, are inherited through GENES, which are located in pairs on microscopic structures inside of cells, called CHROMOSOMES.  They are found in the nucleus of every cell, and made up of strands of DNA.  Genes exist in pairs.

However, the specialized-for-reproduction nucleus of an egg or a sperm cell has only one of each gene from the individual producing it.

Horses, like all mammals, get one of each gene from the mother, and one of each gene from the father, ending up with a pair for every possible characteristic. 

Red vs. Black (E vs. e)

All horses have RED (e) pigment in their coats, manes and tails; and many also have BLACK (E). 

Red-only is usually called CHESTNUT, and is the same, according to presently known genetics, as SORREL. 
Colors like Palomino, Gold (champagne) and red dun are built upon this red-pigment-only base.

Horses with BLACK pigment also include bay, brown, and solid black, and all modifications of those, such as Amber (champagne), brown cream, and grulla.

These exist as one pair of genes on every horse's chromosome.  They determine what pigment is present in a horse's hair.

GENE WARS?  Dominant and recessive genes

So, what if a horse gets a red-hair gene (e) from its father (sire), and a black-hair gene (E) from its mother (dam)? 

Because, in horse color, BLACK is a DOMINANT gene, which means it will always show itself whether there are one or two of them,  it will have black pigment.

But what about that red gene (e)? RED is RECESSIVE in horse color, which means that it can only show up if there is no dominant (E) gene at that "spot" (the red-black spot).

So, the only horses that will be RED (and its derivatives) are ones that get a red gene from BOTH parents.   Two red genes are needed to make a red horse. (ee)

These two make black-based horses:  EE or Ee.

Modifying black:  Agouti (bay, brown, or solid)

We've only discussed one LOCUS (spot where a pair of genes exists) on the horse's chromosome, so far: the E/e locus.  Now we move on to another one, the AGOUTI locus, which contains a pair of genes that only affect black pigment.

This means that if a horse has only red pigment (is "ee" at the red/black locus), the genes at the agouti locus have no effect on that horse's color. 

If the horse DOES have an "E" gene, meaning it does have black pigment, the agouti genes affect it as follows:

•  A, or the BAY AGOUTI gene, when present on a horse with an E (black pigment) gene, will limit the black pigment to the points (mane, tail, lower legs) of the horse.  A/bay is the "most dominant" of the agouti genes, and will always be active when it's present.

•  A^t, or the BROWN AGOUTI gene, when present and active (no A gene) on a horse with an E (black pigment) gene, will allow the black pigment to spread over most of the body, but restrict it on the muzzle and underbelly, etc., causing those areas to be a tan color.  A^t/brown  is the "second most dominant" of the agouti genes, and will be active if no A/bay gene is present

•  a, or the BLACK AGOUTI gene, when present and active (no A ot A^t gene) on a horse with an E (black pigment) gene, allows the black pigment to spread through every bit of the horse's coat.  This produces a solid black horse, or one of its derivatives, depending upon what other genes are present at other loci.  a/solid black is the RECESSIVE gene at the agouti locus, and will only be active when no A/bay or A^t/brown gene is present (aa only).

Just as black is dominant over red at the red/black locus, bay is dominant over brown and solid black, and brown is dominant over solid black, at the agouti locus.

	Chestnut (or "sorrel") (ee) red pigment only any agouti; has no effect on red
	Bay (EE or Ee) black pigment  (AA, AAt or Aa) bay agouti
	Brown (EE or Ee) black pigment (AtAt or Ata) brown agouti
	Black (EE or Ee) black pigment (aa) two solid (black) agouti

Enter the Champagne Gene!

The Champagne gene dilutes red to a golden color, and black to a brown or dark taupe color.

The Champagne gene is also dominant.  So if a horse has even one Champagne in the pair, it will be a Champagne horse.  Ch is the genetic code for Champagne and ch stands for non-Champagne, so:

• Ch+Ch = Champagne horse

• Ch+ch = Champagne horse

• ch+ ch = non-Champagne horse

Now let's look at combinations of all of these:
The Red/Black, the 3 Agoutis, and the Champagne genes.

NOTE: on this web site, as in most genetic notation, an underlined blank spot like this: ___
indicates that it doesn't matter which of the other genes of that pair is present.

Example: an E_ A_ horse will be bay,
and could actually be any of these:

EE AA   (bay)

EE AA^t   (bay)

EE Aa   (bay)

Ee AA   (bay)

Ee AA^t   (bay)

Ee Aa   (bay)

EE AA ChCh  (homozygous for all of these dominant genes)

This horse has two black genes, two bay genes, and two Champagne genes.  So it has black pigment, but only on the points (bay) and that black will be diluted to dark brown (Champagne).  The body is left red by the bay gene, so the Champagne gene makes the body a golden/tan color.  This horse is an Amber!  It may be mistaken for a buckskin, but it has brown points, not black, and pink skin with freckles.

Every one of its foals will be bay based & champagne -- some variation of Amber -- no matter what color mate it's bred to, because every one of its foals will have an E, an A, and a Ch gene from it, which are dominant over all other genes at each of those loci.

Ee Aa Chch  (heterozygous for all genes)

This horse has one each of these dominant genes, so it is the same as the one above, because a dominant gene always shows!

There is a 50% chance that any one of its foals could get any one of its genes ... and since some of those are recessive, the genes of the other parent could be dominant over those, determining its color.

Ee A^ta Chch  (heterozygous for all genes)

This horse is black based, and champagne, but since the A^t gene is dominant over the a gene, and there is no A gene, it is a brown-based champagne, or Sable.

There is a 50% chance that any one of its foals could get any one of its genes ... and since some of those are recessive, the genes of the other parent could be dominant over those, determining its color.

ee (?) Chch   (homozygous for red, agouti unknown, heterozygous for champagne)

This horse has no black pigment (ee is red, which blocks black when there are two and thus, no E) so we cannot tell by looking at it whether it has the bay gene or brown gene or neither (A, A^t or a).  It would require a close look at its parentage & progeny, or an agouti test.  It does have a Champagne gene, so the red is diluted to gold.  This horse will be a Gold.  Often mistaken for Palominos, these horses may or may not have flaxen (white) manes & tails.

As with any mammal, there is a 50% chance that any one of its foals could get any one of its genes ... and since some of those are recessive, the genes of the other parent could be dominant over those, determining its color.

Champagne test now available!

None of the ICHR's conclusions have been disproved by this test; and, there is now a foolproof way to prove our conclusions.  See the link(s) to the test here: http://www.ichregistry.com/color_test_info.htm

The following horses have been DNA tested and found to be homozygous for the champagne gene.
This means that they CANNOT HAVE A NON-CHAMPAGNE FOAL. 
Every single one of their foals will be a champagne color of some kind.